# Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas

Stan Chabert, Nicolas Morison, Marie-Josée Buffière, Laurent Guilbaud, Céline Pleindoux, Géraud de Premorel, Philippe Royer, Marie Harruis, Bernard E Vaissière

► To cite this version:

Stan Chabert, Nicolas Morison, Marie-Josée Buffière, Laurent Guilbaud, Céline Pleindoux, et al. Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas. Journal of Economic Entomology, 2023, 117 (1), pp.43-57. 10.1093/jee/toad222. hal-04439768

HAL Id: hal-04439768

https://hal.inrae.fr/hal-04439768

Submitted on 19 Jun 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas

Stan Chabert, Nicolas Morison, Marie-Josée Buffière, Laurent Guilbaud, Céline Pleindoux, Géraud de Premorel, Philippe Royer, Marie Harruis, Bernard E Vaissière

► To cite this version:

Stan Chabert, Nicolas Morison, Marie-Josée Buffière, Laurent Guilbaud, Céline Pleindoux, et al. Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas. Journal of Economic Entomology, 2024, 117 (1), pp.43-57. 10.1093/jee/toad222. hal-04439768

HAL Id: hal-04439768

https://hal.inrae.fr/hal-04439768v1

Submitted on 19 Jun 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas

Stan Chabert¹,²,*†,•, Nicolas Morison¹, Marie-Josée Buffière¹, Laurent Guilbaud¹, Céline Pleindoux¹, Géraud de Premorel¹, Philippe Royer¹, Marie Harruis¹, Bernard E. Vaissière¹,*,†,•

¹UR406 Abeilles et Environnement, Institut National de Recherche pour l'Agriculture, l'alimentation et l'Environnement (INRAE), Site Agroparc, Domaine Saint-Paul, CS 40509, 84914 Avignon Cedex 9, France, ²Department of Entomology and Nematology, University of Florida, 1881 Natural Area Drive, Gainesville, FL 32611, USA ³Corresponding authors, mail: stan.chabert@gmail.com (S.C.); bernard.vaissiere@inrae.fr (B.E.V.)

¹Equal contribution.

Subject Editor: David Tarpy

Received on 6 July 2023; revised on 24 October 2023; accepted on 27 November 2023

The western honey bee (Apis mellifera L.) is the most globally used managed pollinator species, but it can have limited pollinating activity on nectariferous crops displaying anthers isolated from stigmas, i.e., when anthers are spatially or temporally separated from stigma within or between flowers. We supplemented honey bee colonies with pollen in the combs or in paste form laid on top of the hive frames to test if these treatments could reduce their pollen foraging and increase their pollinating activity in a monoecious and nectariferous cultivar of cantaloupe melon (Cucumis melo L.), in comparison with control colonies not supplemented. We recorded the pollen forager density per flower, the number of pollen grains deposited per stigma and their resulting fruit set, seed set and fruit mass, before and after the colony pollen supplementations. The number of pollen grains deposited by honey bees on stigmas increased gradually after pollen supplementation in the combs. But pollen foraging decreased only moderately, and no effect could be observed on any yield component except the seed set. On the other hand, there was no effect of the pollen paste laid on top of the frames either on stigmatic pollen loads, on colony pollen foraging or on any yield component. Supplementing honey bee colonies with pollen in the combs can therefore be an effective means for increasing their pollinating activity in nectariferous crops displaying anthers isolated from stigmas, e.g., Amaryllidaceae, Apiaceae, Cucurbitaceae, avocado, all hybrid seed productions. The context for the potential use of pollen substitutes is discussed.

Key words: cantaloupe melon, honey bee colony, pollen supplementation, pollinating activity, stigmatic pollen load

## Introduction

Many crops need insect pollinators to set seeds and fruits (Klein et al. 2007), and managed pollinators are often used in addition to the wild entomofauna to fulfill this need (Isaacs et al. 2017). The western honey bee (Apis mellifera L. [Hymenoptera: Apidae]; hereafter 'honey bee'), is the most globally used managed pollinator species, both in fields and under enclosures. It is often the most effective crop pollinator due to its abundance, however, it is not the most efficient per flower visit in many cases (Rader et al. 2009, Garibaldi et al. 2013, Hung et al. 2018, Page et al. 2021, Junqueira et al. 2022). To increase the pollinating activity of honey bees in crops, growers

usually try to increase the honey bee density by increasing the colony stocking rate, while this practice does not necessarily result in better yields and can even be detrimental (Aizen et al. 2014, 2020, Gaines-Day and Gratton 2016, Rollin and Garibaldi 2019).

The limited pollination performance of honey bees can be explained by several behavioral traits. First, honey bees can have limited single-visit pollen depositions (Hung et al. 2018, Földesi et al. 2021, Page et al. 2021). This behavioral trait may result at least partly from their intermediate body size and limited hairiness (Stavert et al. 2016, Roquer-Beni et al. 2020, Földesi et al. 2021). Honey bees can also have poor flower handling behavior
# Supplementing honey bee (Hymenoptera: Apidae) colonies with pollen increases their pollinating activity on nectariferous crops with anthers isolated from stigmas

Stan Chabert¹,²,*†,•, Nicolas Morison¹, Marie-Josée Buffière¹, Laurent Guilbaud¹, Céline Pleindoux¹, Géraud de Premorel¹, Philippe Royer¹, Marie Harruis¹, Bernard E. Vaissière¹,*,†,•

¹UR406 Abeilles et Environnement, Institut National de Recherche pour l'Agriculture, l'alimentation et l'Environnement (INRAE), Site Agroparc, Domaine Saint-Paul, CS 40509, 84914 Avignon Cedex 9, France, ²Department of Entomology and Nematology, University of Florida, 1881 Natural Area Drive, Gainesville, FL 32611, USA ³Corresponding authors, mail: stan.chabert@gmail.com (S.C.); bernard.vaissiere@inrae.fr (B.E.V.)

¹Equal contribution.

Subject Editor: David Tarpy

Received on 6 July 2023; revised on 24 October 2023; accepted on 27 November 2023

The western honey bee (Apis mellifera L.) is the most globally used managed pollinator species, but it can have limited pollinating activity on nectariferous crops displaying anthers isolated from stigmas, i.e., when anthers are spatially or temporally separated from stigma within or between flowers. We supplemented honey bee colonies with pollen in the combs or in paste form laid on top of the hive frames to test if these treatments could reduce their pollen foraging and increase their pollinating activity in a monoecious and nectariferous cultivar of cantaloupe melon (Cucumis melo L.), in comparison with control colonies not supplemented. We recorded the pollen forager density per flower, the number of pollen grains deposited per stigma and their resulting fruit set, seed set and fruit mass, before and after the colony pollen supplementations. The number of pollen grains deposited by honey bees on stigmas increased gradually after pollen supplementation in the combs. But pollen foraging decreased only moderately, and no effect could be observed on any yield component except the seed set. On the other hand, there was no effect of the pollen paste laid on top of the frames either on stigmatic pollen loads, on colony pollen foraging or on any yield component. Supplementing honey bee colonies with pollen in the combs can therefore be an effective means for increasing their pollinating activity in nectariferous crops displaying anthers isolated from stigmas, e.g., Amaryllidaceae, Apiaceae, Cucurbitaceae, avocado, all hybrid seed productions. The context for the potential use of pollen substitutes is discussed.

Key words: cantaloupe melon, honey bee colony, pollen supplementation, pollinating activity, stigmatic pollen load

## Introduction

Many crops need insect pollinators to set seeds and fruits (Klein et al. 2007), and managed pollinators are often used in addition to the wild entomofauna to fulfill this need (Isaacs et al. 2017). The western honey bee (Apis mellifera L. [Hymenoptera: Apidae]; hereafter ‘honey bee’), is the most globally used managed pollinator species, both in fields and under enclosures. It is often the most effective crop pollinator due to its abundance, however, it is not the most efficient per flower visit in many cases (Rader et al. 2009, Garibaldi et al. 2013, Hung et al. 2018, Page et al. 2021, Junqueira et al. 2022). To increase the pollinating activity of honey bees in crops, growers

usually try to increase the honey bee density by increasing the colony stocking rate, while this practice does not necessarily result in better yields and can even be detrimental (Aizen et al. 2014, 2020, Gaines-Day and Gratton 2016, Rollin and Garibaldi 2019).

The limited pollination performance of honey bees can be explained by several behavioral traits. First, honey bees can have limited single-visit pollen depositions (Hung et al. 2018, Földesi et al. 2021, Page et al. 2021). This behavioral trait may result at least partly from their intermediate body size and limited hairiness (Stavert et al. 2016, Roquer-Beni et al. 2020, Földesi et al. 2021). Honey bees can also have poor flower handling behavior
for pollination such as nectar theft, a behavior in which they visit flowers from the side to get access to the nectar without contacting the reproductive structures (e.g., Dedej and Delaplane 2005, Park et al. 2016). The pollen carried by pollen foragers in their corbiculae or on their bodies has poor viability compared to the pollen carried by nectar foragers on their bodies or by noncorbiculate bees in their scopae, as honey bee pollen foragers moisten the pollen with oral secretions that affect its viability when grooming (Vaissière et al. 1996, Parker et al. 2015). Honey bees are not particularly effective in transferring cross-pollen on cultivars requiring cross-pollination, especially when wild entomofauna is absent (Jackson 1996, Brittain et al. 2013, Garibaldi et al. 2013, Eeraerts et al. 2020). Finally, honey bees forage in a large area around their nest and they communicate to each other the locations of the most profitable flower patches with dances, resulting in a high ability to be diluted around the target crop on attractive competing blooms (Jay 1986, Osterman et al. 2021, Farina et al. 2023).

To mitigate these behavioral traits of honey bees for pollination, various management methods have been proposed to improve their pollinating activity. For instance, to recruit and direct foragers towards the target crop, beekeepers can feed colonies with caffeine- or arginine-treated sugar syrup scented with the crop floral odors before the onset of flowering (Farina et al. 2023), or they can introduce colonies sequentially into the crop to offset the gradual increase of foraging range that occurs after colony relocation (Al-Tikrity et al. 1972, Gary et al. 1978, Mayer 1994, Shafir 2011). In hermaphrodite crops that experience nectar theft from nectar foragers and for which pollen foragers are better pollinators, like apple tree (Malus domestica Borkh. [Rosales: Rosaceae]; Robinson and Fell 1981, Thomson and Goodell 2001), or in crops that rely only on pollen foragers for pollination such as kiwifruit (Actinidia deliciosa C. F. Liang & A. R. Ferguson C. F. Liang & A. R. Ferguson [Ericales: Actinidiaceae]), some authors have proposed to increase the pollen foraging activity by fitting hives with pollen traps (Webster et al. 1985, Gemeda et al. 2018), by treating them with brood pheromone (Pankiw 2004, Sagili et al. 2015), or by removing pollen stores (Tsirakoglou et al. 1997). The sequential introduction of colonies and the provision of bumble bee colonies or mason bees can also help decreasing honey bee nectar theft and enhancing cross-pollination by increasing honey bee movements between rows of different cultivars (Stern et al. 2001, 2004, 2005, Brittain et al. 2013, Sapir et al. 2017, Eeraerts et al. 2020). Beekeepers can also feed their colonies with unscented sugar syrup, pollen paste, or pollen substitutes in late winter and during crop flowering to stimulate earlier egg-laying by the queen and thus benefit from more populous colonies, with more sealed and unsealed brood, more foragers including pollen foragers when crops bloom in spring and summer (Goodwin 1997, Kalev et al. 2002, Geslin et al. 2017a, Cavigliasso et al. 2021, Noordyke and Ellis 2021, Hoover et al. 2022). But supplementing colonies with pollen was never contemplated as a means to directly control their level of pollen foraging activity, regardless of colony and unsealed brood size.

Pollen foraging can be responsible for pollen theft, a phenomenon that occurs especially when anthers are isolated from stigmas in nectar-secreting flowers, and especially with honey bees which have been documented as pollen thieves much more frequently than other species (Ish-Am and Eisikowitch, 1993, Young et al. 2007, Hargreaves et al. 2010, 2012, Koski et al. 2018; review in Hargreaves et al. 2009). Isolation of anthers from stigmas occurs when anthers are spatially or temporally separated from stigmas within or between flowers. It appears in a wide range of nectariferous (i.e., with nectar-secreting flowers) entomophilous crop species, listed

in Supplementary Table S1 (62 crop species listed, with definitions of the following botanic words): monoecious (e.g., Cucurbitaceae), (gyno)dioecious (e.g., all hybrid seed crops), (hetero/duo)dichogamous (e.g., avocado, *Persea americana* Mill. Mill. [Laurales: Lauraceae]; Amaryllidaceae, Apiaceae, and Asteraceae seed crops), and herkogamous crop species (e.g., strawberry, *Fragaria × ananassa* Duchesne Duchesne [Rosales: Rosaceae]).

When anthers are isolated from stigmas in nectariferous flower species, pollination is mainly realized by nectar foragers which visit both pistillate and staminate flowers for nectar, while pollen foragers act mainly as pollen thieves by focusing on staminate flowers and removing pollen from the anthers and the plant population without contacting or pollinating stigmas (Ish-Am and Eisikowitch, 1993, Young et al. 2007). In return, this pollen is lost to the plant population while it could have been used by nectar foragers for pollination (Hargreaves et al. 2009, 2010, Koski et al. 2018). In other words, the activity of pollen foragers in such species reduces the pollinating activity of nectar foragers, through a decrease of the pollen available on the body of nectar foragers.

Nectar and pollen foraging are genetically segregated behaviors among honey bee foragers, and pollen foraging has the distinctive feature of being plastic, depending both on the colony pollen needs on one hand, determined by the pollen consumption of adult bees and larvae, and on its pollen stores on the other hand (Fewell and Winston 1992, Camazine 1993, Fewell and Page 1993, 2000, Page et al. 1995, Pankiw et al. 1998, Dreller et al. 1999, Vaughan and Calderone 2002, Pankiw 2004). Pollen foraging is thus regulated around a certain homeostatic set point between pollen consumption and pollen stores (Fewell and Winston 1992, Camazine 1993, Pankiw et al. 1998, Fewell and Bertram 1999, Fewell and Page 2000, Schmickl and Crailsheim 2004), unlike nectar foraging which is activated without limit as long as there is empty space still available in combs to unload nectar (Fewell and Winston 1996). Seeley (1995) assessed that a honey bee colony maintains a sufficient pollen reserve to meet its needs for about 10 days.

Conceptually, when pollen stores are below this set point, the colony pollen foraging is activated, the activation being mostly achieved by the increase in the number of bees foraging for pollen, and, to a lesser extent, through an increased individual foraging effort of the bees already involved in pollen collection. This can take place through the increase in the number of trips achieved per day, the time spent outside the nest, and the size of the pollen loads they return with to the nest (Fewell and Winston 1992, Fewell and Page 1993, 2000, Pankiw et al. 1998, Fewell and Bertram 1999, Janmaat et al. 2000, Rotjan et al. 2002, Weidenmüller and Tautz 2002, Pankiw 2004). Conversely, when pollen stores are above this set point, pollen foraging is inhibited, with only a few foragers still actively collecting pollen and with a decreased individual foraging effort (Camazine 1993, Fewell and Bertram 1999, Fewell and Page 2000, Janmaat et al. 2000, Weidenmüller and Tautz 2002). When pollen foraging is activated, new pollen foragers are recruited mostly from previously nonforager and nest-related tasks-occupied bees, and, to a lesser extent, among previously nectar foragers (Fewell and Bertram 1999, Rotjan et al. 2002; but see Fewell and Page 1993). Conversely, when pollen foraging is inhibited, bees that stop foraging for pollen mostly just stop foraging altogether and stay in the nest, and only a few of them switch to nectar foraging (Camazine 1993). Consequently, we can expect that supplementing a honey bee colony with pollen in its combs close to unsealed brood can lead to a decrease in its pollen foraging and pollen theft in nectariferous crops displaying anthers isolated from stigmas, and thereby increase the pollinating activity of its nectar foragers through the increased availability of pollen in the crop and on their body.
for pollination such as nectar theft, a behavior in which they visit flowers from the side to get access to the nectar without contacting the reproductive structures (e.g., Dedej and Delaplane 2005, Park et al. 2016). The pollen carried by pollen foragers in their corbiculae or on their bodies has poor viability compared to the pollen carried by nectar foragers on their bodies or by noncorbiculate bees in their scopae, as honey bee pollen foragers moisten the pollen with oral secretions that affect its viability when grooming (Vaissière et al. 1996, Parker et al. 2015). Honey bees are not particularly effective in transferring cross-pollen on cultivars requiring cross-pollination, especially when wild entomofauna is absent (Jackson 1996, Brittain et al. 2013, Garibaldi et al. 2013, Eeraerts et al. 2020). Finally, honey bees forage in a large area around their nest and they communicate to each other the locations of the most profitable flower patches with dances, resulting in a high ability to be diluted around the target crop on attractive competing blooms (Jay 1986, Osterman et al. 2021, Farina et al. 2023).

To mitigate these behavioral traits of honey bees for pollination, various management methods have been proposed to improve their pollinating activity. For instance, to recruit and direct foragers towards the target crop, beekeepers can feed colonies with caffeine- or arginine-treated sugar syrup scented with the crop floral odors before the onset of flowering (Farina et al. 2023), or they can introduce colonies sequentially into the crop to offset the gradual increase of foraging range that occurs after colony relocation (Al-Tikrity et al. 1972, Gary et al. 1978, Mayer 1994, Shafir 2011). In hermaphrodite crops that experience nectar theft from nectar foragers and for which pollen foragers are better pollinators, like apple tree (Malus domestica Borkh. [Rosales: Rosaceae]; Robinson and Fell 1981, Thomson and Goodell 2001), or in crops that rely only on pollen foragers for pollination such as kiwifruit (Actinidia deliciosa C. F. Liang & A. R. Ferguson C. F. Liang & A. R. Ferguson [Ericales: Actinidiaceae]), some authors have proposed to increase the pollen foraging activity by fitting hives with pollen traps (Webster et al. 1985, Gemeda et al. 2018), by treating them with brood pheromone (Pankiw 2004, Sagili et al. 2015), or by removing pollen stores (Tsirakoglou et al. 1997). The sequential introduction of colonies and the provision of bumble bee colonies or mason bees can also help decreasing honey bee nectar theft and enhancing cross-pollination by increasing honey bee movements between rows of different cultivars (Stern et al. 2001, 2004, 2005, Brittain et al. 2013, Sapir et al. 2017, Eeraerts et al. 2020). Beekeepers can also feed their colonies with unscented sugar syrup, pollen paste, or pollen substitutes in late winter and during crop flowering to stimulate earlier egg-laying by the queen and thus benefit from more populous colonies, with more sealed and unsealed brood, more foragers including pollen foragers when crops bloom in spring and summer (Goodwin 1997, Kalev et al. 2002, Geslin et al. 2017a, Cavigliasso et al. 2021, Noordyke and Ellis 2021, Hoover et al. 2022). But supplementing colonies with pollen was never contemplated as a means to directly control their level of pollen foraging activity, regardless of colony and unsealed brood size.

Pollen foraging can be responsible for pollen theft, a phenomenon that occurs especially when anthers are isolated from stigmas in nectar-secreting flowers, and especially with honey bees which have been documented as pollen thieves much more frequently than other species (Ish-Am and Eisikowitch, 1993, Young et al. 2007, Hargreaves et al. 2010, 2012, Koski et al. 2018; review in Hargreaves et al. 2009). Isolation of anthers from stigmas occurs when anthers are spatially or temporally separated from stigmas within or between flowers. It appears in a wide range of nectariferous (i.e., with nectar-secreting flowers) entomophilous crop species, listed

in Supplementary Table S1 (62 crop species listed, with definitions of the following botanic words): monoecious (e.g., Cucurbitaceae), (gyno)dioecious (e.g., all hybrid seed crops), (hetero/duo)dichogamous (e.g., avocado, *Persea americana* Mill. Mill. [Laurales: Lauraceae]; Amaryllidaceae, Apiaceae, and Asteraceae seed crops), and herkogamous crop species (e.g., strawberry, *Fragaria × ananassa* Duchesne Duchesne [Rosales: Rosaceae]).

When anthers are isolated from stigmas in nectariferous flower species, pollination is mainly realized by nectar foragers which visit both pistillate and staminate flowers for nectar, while pollen foragers act mainly as pollen thieves by focusing on staminate flowers and removing pollen from the anthers and the plant population without contacting or pollinating stigmas (Ish-Am and Eisikowitch, 1993, Young et al. 2007). In return, this pollen is lost to the plant population while it could have been used by nectar foragers for pollination (Hargreaves et al. 2009, 2010, Koski et al. 2018). In other words, the activity of pollen foragers in such species reduces the pollinating activity of nectar foragers, through a decrease of the pollen available on the body of nectar foragers.

Nectar and pollen foraging are genetically segregated behaviors among honey bee foragers, and pollen foraging has the distinctive feature of being plastic, depending both on the colony pollen needs on one hand, determined by the pollen consumption of adult bees and larvae, and on its pollen stores on the other hand (Fewell and Winston 1992, Camazine 1993, Fewell and Page 1993, 2000, Page et al. 1995, Pankiw et al. 1998, Dreller et al. 1999, Vaughan and Calderone 2002, Pankiw 2004). Pollen foraging is thus regulated around a certain homeostatic set point between pollen consumption and pollen stores (Fewell and Winston 1992, Camazine 1993, Pankiw et al. 1998, Fewell and Bertram 1999, Fewell and Page 2000, Schmickl and Crailsheim 2004), unlike nectar foraging which is activated without limit as long as there is empty space still available in combs to unload nectar (Fewell and Winston 1996). Seeley (1995) assessed that a honey bee colony maintains a sufficient pollen reserve to meet its needs for about 10 days.

Conceptually, when pollen stores are below this set point, the colony pollen foraging is activated, the activation being mostly achieved by the increase in the number of bees foraging for pollen, and, to a lesser extent, through an increased individual foraging effort of the bees already involved in pollen collection. This can take place through the increase in the number of trips achieved per day, the time spent outside the nest, and the size of the pollen loads they return with to the nest (Fewell and Winston 1992, Fewell and Page 1993, 2000, Pankiw et al. 1998, Fewell and Bertram 1999, Janmaat et al. 2000, Rotjan et al. 2002, Weidenmüller and Tautz 2002, Pankiw 2004). Conversely, when pollen stores are above this set point, pollen foraging is inhibited, with only a few foragers still actively collecting pollen and with a decreased individual foraging effort (Camazine 1993, Fewell and Bertram 1999, Fewell and Page 2000, Janmaat et al. 2000, Weidenmüller and Tautz 2002). When pollen foraging is activated, new pollen foragers are recruited mostly from previously nonforager and nest-related tasks-occupied bees, and, to a lesser extent, among previously nectar foragers (Fewell and Bertram 1999, Rotjan et al. 2002; but see Fewell and Page 1993). Conversely, when pollen foraging is inhibited, bees that stop foraging for pollen mostly just stop foraging altogether and stay in the nest, and only a few of them switch to nectar foraging (Camazine 1993). Consequently, we can expect that supplementing a honey bee colony with pollen in its combs close to unsealed brood can lead to a decrease in its pollen foraging and pollen theft in nectariferous crops displaying anthers isolated from stigmas, and thereby increase the pollinating activity of its nectar foragers through the increased availability of pollen in the crop and on their body.
Cantaloupe melon (Cucumis melo L. [Cucurbitales: Cucurbitaceae]; hereafter 'melon') is a self-compatible and self-fertile crop which relies entirely on insects for pollination and fruit production, and growers use honey bees worldwide to ensure adequate pollination and getting marketable fruits (Mann 1953, Bohn and Davis 1964, Norden 1985, Kouonon et al. 2009, Delaplane 2023). Grown in open fields or in enclosures (e.g., Dag and Eisikowitch 1995, Rodrigo Gomez et al. 2021), melon production continuously increased during the last 60 yr, along with the global area harvested and yield, to reach 28.6 million tons in the world in 2021, with China accounting for 49% of this total (Supplementary Fig. S1; FAOSTAT 2023). It is also a crop that is strongly resource limited and sets into fruits only a small fraction of its pistillate flowers, even when these flowers are well-pollinated (Mann and Robinson 1950, Mann 1953, Norden 1985, Valantin et al. 1999, Valantin-Morison et al. 2006, Pitrat 2008). Flowers last only 1 day, with anthesis occurring in the morning (Norden 1985, Revanasidda and Belavadi 2019). Most cultivars are andromonoecious, but some are monoecious (Pitrat 2008, 2013). Both pistillate and staminate flowers secrete nectar from anthesis until early afternoon (Orr and Eisikowitch 1988, Dag and Eisikowitch 1999), pollen is also released over this period in staminate flowers (Mann 1953, Orr and Eisikowitch 1988), and the stigma is receptive during this period as well in pistillate flowers (Norden 1985). Consequently, bee foraging and pollination occur mostly during this period (Grewal and Sidhu 1983, Dag and Eisikowitch 1995, 1999, Vaissière and Froissart 1996, Tschoeke et al. 2015). Honey bees forage in melon flowers for both pollen

and nectar (Mann 1953, Vaissière et al. 1996). Pistillate flowers require a minimum of 10–15 bee visits per flower to maximize fruit set and fruit size (McGregor et al. 1965, Grewal and Sidhu 1983, Revanasidda and Belavadi 2019).

The aim of our study was to test if supplementing combs of honey bee colonies with pollen could increase their pollinating activity in a nectariferous crop with anthers isolated from stigmas. We used a monoecious cultivar of cantaloupe melon grown in enclosures, to ensure that the crop was pollinated by the treated colonies, and only by them. To assess the colony pollinating activity, we counted the number of melon pollen grains deposited onto stigmas. The resulting fruit set, seed set, and fruit mass were also recorded, although we did not necessarily expect an effect of supplementing honey bee colonies with pollen on these variables since melon production is strongly resource limited. Despite its strong resource limitation, melon crop has the advantage of having flowers that last only 1 day, which enabled us to have multiple independent repetitions by sampling the stigmatic pollen loads over several independent days. We also had a method to count the pollen grains on dry stigmas for this species (Vaissière and Froissart 1996), enabling us to use melon as a model for proof of concept for our hypothesis. In addition, we also supplemented colonies with pollen in paste form laid on top of the hive frames, as it is commonly used to increase the colony and brood size, and sometimes in crop pollination contexts (Kalev et al. 2002, Noordyke and Ellis 2021, Hoover et al. 2022), to test if it might provide an easier means to decrease the colony pollen foraging and increase their pollinating activity.

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** (A) Insertion of thawed bee pollen pellets in the combs. (B) Spraying of saccharose syrup on the combs. (C) The pollen pellets sprayed with syrup remain in the combs when the frame is held vertically. (D) All the pollen pellets have been packed into bee bread and partly consumed by the honey bees one week after. Photo credit: Cyril Scomparin/INRAE and Stan Chabert/INRAE.</figcaption></figure>
Cantaloupe melon (Cucumis melo L. [Cucurbitales: Cucurbitaceae]; hereafter 'melon') is a self-compatible and self-fertile crop which relies entirely on insects for pollination and fruit production, and growers use honey bees worldwide to ensure adequate pollination and getting marketable fruits (Mann 1953, Bohn and Davis 1964, Norden 1985, Kouonon et al. 2009, Delaplane 2023). Grown in open fields or in enclosures (e.g., Dag and Eisikowitch 1995, Rodrigo Gomez et al. 2021), melon production continuously increased during the last 60 yr, along with the global area harvested and yield, to reach 28.6 million tons in the world in 2021, with China accounting for 49% of this total (Supplementary Fig. S1; FAOSTAT 2023). It is also a crop that is strongly resource limited and sets into fruits only a small fraction of its pistillate flowers, even when these flowers are well-pollinated (Mann and Robinson 1950, Mann 1953, Norden 1985, Valantin et al. 1999, Valantin-Morison et al. 2006, Pitrat 2008). Flowers last only 1 day, with anthesis occurring in the morning (Norden 1985, Revanasidda and Belavadi 2019). Most cultivars are andromonoecious, but some are monoecious (Pitrat 2008, 2013). Both pistillate and staminate flowers secrete nectar from anthesis until early afternoon (Orr and Eisikowitch 1988, Dag and Eisikowitch 1999), pollen is also released over this period in staminate flowers (Mann 1953, Orr and Eisikowitch 1988), and the stigma is receptive during this period as well in pistillate flowers (Norden 1985). Consequently, bee foraging and pollination occur mostly during this period (Grewal and Sidhu 1983, Dag and Eisikowitch 1995, 1999, Vaissière and Froissart 1996, Tschoeke et al. 2015). Honey bees forage in melon flowers for both pollen

and nectar (Mann 1953, Vaissière et al. 1996). Pistillate flowers require a minimum of 10–15 bee visits per flower to maximize fruit set and fruit size (McGregor et al. 1965, Grewal and Sidhu 1983, Revanasidda and Belavadi 2019).

The aim of our study was to test if supplementing combs of honey bee colonies with pollen could increase their pollinating activity in a nectariferous crop with anthers isolated from stigmas. We used a monoecious cultivar of cantaloupe melon grown in enclosures, to ensure that the crop was pollinated by the treated colonies, and only by them. To assess the colony pollinating activity, we counted the number of melon pollen grains deposited onto stigmas. The resulting fruit set, seed set, and fruit mass were also recorded, although we did not necessarily expect an effect of supplementing honey bee colonies with pollen on these variables since melon production is strongly resource limited. Despite its strong resource limitation, melon crop has the advantage of having flowers that last only 1 day, which enabled us to have multiple independent repetitions by sampling the stigmatic pollen loads over several independent days. We also had a method to count the pollen grains on dry stigmas for this species (Vaissière and Froissart 1996), enabling us to use melon as a model for proof of concept for our hypothesis. In addition, we also supplemented colonies with pollen in paste form laid on top of the hive frames, as it is commonly used to increase the colony and brood size, and sometimes in crop pollination contexts (Kalev et al. 2002, Noordyke and Ellis 2021, Hoover et al. 2022), to test if it might provide an easier means to decrease the colony pollen foraging and increase their pollinating activity.

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** (A) Insertion of thawed bee pollen pellets in the combs. (B) Spraying of saccharose syrup on the combs. (C) The pollen pellets sprayed with syrup remain in the combs when the frame is held vertically. (D) All the pollen pellets have been packed into bee bread and partly consumed by the honey bees one week after. Photo credit: Cyril Scomparin/INRAE and Stan Chabert/INRAE.</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** (A, B) Mixing of bee pollen pellets with saccharose syrup to prepare the pollen paste. (C, D) Deposition of the pollen paste on top of the hive frames. (E) The pollen paste has been partly consumed by the honey bees one week after. Photo credit: Laurent Guilbaud/INRAE and Nicolas Morison/INRAE.</figcaption></figure>

<table><caption>**Table 1.** Statistics of the GLMMs computed to test the differences of flower number, assessed in 8 m transects per tunnel per sampling day, between the 3 colony treatments</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="6">Number of pistillate flowers per 8 m transect</td><td>Intercept: control - BT</td><td>2.705 ± 0.169</td><td>17.02</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-0.348 ± 0.267</td><td>-1.30</td><td>0.193</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.085 ± 0.110</td><td>0.77</td><td>0.439</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.195 ± 0.107</td><td>1.82</td><td>0.069</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.126 ± 0.198</td><td>-0.64</td><td>0.525</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-0.117 ± 0.193</td><td>-0.61</td><td>0.544</td><td></td></tr><tr><td rowspan="6">Number of staminate flowers per 8 m transect</td><td>Intercept: control - BT</td><td>4.369 ± 0.395</td><td>11.05</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>0.032 ± 0.088</td><td>0.36</td><td>0.716</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.117 ± 0.556</td><td>0.21</td><td>0.833</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.052 ± 0.556</td><td>0.09</td><td>0.925</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.076 ± 0.075</td><td>-1.02</td><td>0.308</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-0.128 ± 0.077</td><td>-1.68</td><td>0.094</td><td>Weak</td></tr><tr><td rowspan="6">% of staminate flowers</td><td>Intercept: control - BT</td><td>1.659 ± 0.134</td><td>12.41</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>0.384 ± 0.227</td><td>1.70</td><td>0.090</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.074 ± 0.120</td><td>0.62</td><td>0.535</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-0.107 ± 0.117</td><td>-0.92</td><td>0.360</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>0.053 ± 0.214</td><td>0.25</td><td>0.802</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-0.003 ± 0.209</td><td>-0.01</td><td>0.989</td><td></td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022).
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** (A, B) Mixing of bee pollen pellets with saccharose syrup to prepare the pollen paste. (C, D) Deposition of the pollen paste on top of the hive frames. (E) The pollen paste has been partly consumed by the honey bees one week after. Photo credit: Laurent Guilbaud/INRAE and Nicolas Morison/INRAE.</figcaption></figure>

<table><caption>**Table 1.** Statistics of the GLMMs computed to test the differences of flower number, assessed in 8 m transects per tunnel per sampling day, between the 3 colony treatments</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="6">Number of pistillate flowers per 8 m transect</td><td>Intercept: control - BT</td><td>2.705 ± 0.169</td><td>17.02</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-0.348 ± 0.267</td><td>-1.30</td><td>0.193</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.085 ± 0.110</td><td>0.77</td><td>0.439</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.195 ± 0.107</td><td>1.82</td><td>0.069</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.126 ± 0.198</td><td>-0.64</td><td>0.525</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-0.117 ± 0.193</td><td>-0.61</td><td>0.544</td><td></td></tr><tr><td rowspan="6">Number of staminate flowers per 8 m transect</td><td>Intercept: control - BT</td><td>4.369 ± 0.395</td><td>11.05</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>0.032 ± 0.088</td><td>0.36</td><td>0.716</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.117 ± 0.556</td><td>0.21</td><td>0.833</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.052 ± 0.556</td><td>0.09</td><td>0.925</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.076 ± 0.075</td><td>-1.02</td><td>0.308</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-0.128 ± 0.077</td><td>-1.68</td><td>0.094</td><td>Weak</td></tr><tr><td rowspan="6">% of staminate flowers</td><td>Intercept: control - BT</td><td>1.659 ± 0.134</td><td>12.41</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>0.384 ± 0.227</td><td>1.70</td><td>0.090</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.074 ± 0.120</td><td>0.62</td><td>0.535</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-0.107 ± 0.117</td><td>-0.92</td><td>0.360</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>0.053 ± 0.214</td><td>0.25</td><td>0.802</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-0.003 ± 0.209</td><td>-0.01</td><td>0.989</td><td></td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022).
# Materials and Methods

## Study Sites and Crop Model

This study was carried out from April to June 2011 in 6 commercial tunnels located in Avignon in a commercial farm (France; 43°54'46.12"N, 4°52'35.64"E). The vents of the 71 m long × 9.4 m wide tunnels were covered with insectproof polyethylene crystal screen with 8 mm × 3 mm openings (F1028Q; Diatex, France) to prevent honey bees from leaving the tunnels. Each tunnel was sown with 4 rows of the monoecious cantaloupe melon cv. F₁ hybrid "Neo" (Cucumis melo L. ssp. melo var. cantalupensis horticultural group "Charentais"; Supplementary Fig. S2).

## Experimental Setup, and Counts of Flowers and Honey Bee Foragers

The experiment was organized in 2 repetitions of 3 tunnels each, the samplings occurring every 2 days from 28 April to 12 May 2011 for the first repetition, and from 13 May to 27 May 2011 for the second repetition, with 8 sampling days for each repetition. One small honey bee colony in a 5-frame Dadant hive supplied from a standard apiary was introduced in each tunnel, as usually practiced on the farm, at 13:00 UTC (3 PM) 2 days before the beginning of the samplings. A different colony was used for each repetition. The pistillate and staminate flowers were counted on each sampling day at ca. 12:00 UTC (2 PM) in each tunnel in 4 plots 2 m long distributed around the geometric center of each tunnel and located at least 5 m apart from the tunnel edges (see Supplementary Fig. S3), each plot being in a different row. Honey bee foragers were counted twice on each sampling day at ca. 08:00 UTC (10 AM) and 12:00 UTC (2 PM) on 200 flowers randomly chosen each time in each tunnel. Each flower was scanned once by recording if a bee was foraging in it or not at the time of observation (instantaneous count; Vaissière et al. 2011, Garibaldi et al. 2016). The same flowers could be observed at 08:00 UTC (10 AM) and then again at 12:00 UTC (2 PM) depending on the random choice. The 200 flowers were divided into 4 transects, with 1 transect of 50 flowers per row. Each transect started from the plot of flower count and headed towards the geometric center of each tunnel (Vaissière et al. 2011; see Supplementary Fig. S3). The scanned flowers were either pistillate or staminate at random. For each forager scanned, we recorded the presence or absence of pollen in its corbiculae.

## Assessment of Honey Bee Colonies and Pollen Supplementation Treatments

In the evening of the 5th sampling day of each repetition, i.e., 6 May for repetition 1 and 21 May for repetition 2, each honey bee colony was assessed at night. The frames, the hive, and the bottom board of each colony were shaken and brushed above an empty swarm box at night with the aim to catch all the adult bees of the colony in the box. This box was weighed, and its empty mass subtracted to get the mass of the bee population. When the bees were returned to their hive, a sample of ca. 100 bees was taken from the population, frozen, weighed, and counted later to obtain the mean mass per bee. This mean mass was used to convert the mass of the bee population into a number of bees (Farrar 1937, Chabert et al. 2021). The areas of unsealed and sealed brood, and of pollen and honey stores were assessed for each colony by placing a clear acrylic plexiglass sheet on each frame side and by drawing the outline of each component with a marker. The drawn areas were then analyzed with the plugin *Versatile Wand Tool* (https://imagej.nih.gov/ij/plugins/versatile-wand-tool/index.html) of the software ImageJ (Schneider et al. 2012). The colony features are given in Supplementary Table S2.

These features enabled us to calculate that the amount of 1 kg of pollen used for the pollen supplementation treatments (see below) was large enough to exceed the homeostatic set point beyond which the colonies decrease their pollen collection: 1 kg of pollen was equivalent to more than 3 wk of pollen consumption of the colony presenting the highest daily pollen consumption, while a honey bee

<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Variation of the flower number (mean ± SE) assessed in 4 plots 2 m long per tunnel per sampling day before (5 sampling days) and after (3 sampling days) colony treatment. The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. #: indicates weak statistical evidence of the interaction between the colony treatment (control versus pollen supplementation) and the period before/after treatment, i.e., with 0.05 ≤ *P* < 0.1 (Table 1).</figcaption></figure>
# Materials and Methods

## Study Sites and Crop Model

This study was carried out from April to June 2011 in 6 commercial tunnels located in Avignon in a commercial farm (France; 43°54'46.12"N, 4°52'35.64"E). The vents of the 71 m long × 9.4 m wide tunnels were covered with insectproof polyethylene crystal screen with 8 mm × 3 mm openings (F1028Q; Diatex, France) to prevent honey bees from leaving the tunnels. Each tunnel was sown with 4 rows of the monoecious cantaloupe melon cv. F₁ hybrid "Neo" (Cucumis melo L. ssp. melo var. cantalupensis horticultural group "Charentais"; Supplementary Fig. S2).

## Experimental Setup, and Counts of Flowers and Honey Bee Foragers

The experiment was organized in 2 repetitions of 3 tunnels each, the samplings occurring every 2 days from 28 April to 12 May 2011 for the first repetition, and from 13 May to 27 May 2011 for the second repetition, with 8 sampling days for each repetition. One small honey bee colony in a 5-frame Dadant hive supplied from a standard apiary was introduced in each tunnel, as usually practiced on the farm, at 13:00 UTC (3 PM) 2 days before the beginning of the samplings. A different colony was used for each repetition. The pistillate and staminate flowers were counted on each sampling day at ca. 12:00 UTC (2 PM) in each tunnel in 4 plots 2 m long distributed around the geometric center of each tunnel and located at least 5 m apart from the tunnel edges (see Supplementary Fig. S3), each plot being in a different row. Honey bee foragers were counted twice on each sampling day at ca. 08:00 UTC (10 AM) and 12:00 UTC (2 PM) on 200 flowers randomly chosen each time in each tunnel. Each flower was scanned once by recording if a bee was foraging in it or not at the time of observation (instantaneous count; Vaissière et al. 2011, Garibaldi et al. 2016). The same flowers could be observed at 08:00 UTC (10 AM) and then again at 12:00 UTC (2 PM) depending on the random choice. The 200 flowers were divided into 4 transects, with 1 transect of 50 flowers per row. Each transect started from the plot of flower count and headed towards the geometric center of each tunnel (Vaissière et al. 2011; see Supplementary Fig. S3). The scanned flowers were either pistillate or staminate at random. For each forager scanned, we recorded the presence or absence of pollen in its corbiculae.

## Assessment of Honey Bee Colonies and Pollen Supplementation Treatments

In the evening of the 5th sampling day of each repetition, i.e., 6 May for repetition 1 and 21 May for repetition 2, each honey bee colony was assessed at night. The frames, the hive, and the bottom board of each colony were shaken and brushed above an empty swarm box at night with the aim to catch all the adult bees of the colony in the box. This box was weighed, and its empty mass subtracted to get the mass of the bee population. When the bees were returned to their hive, a sample of ca. 100 bees was taken from the population, frozen, weighed, and counted later to obtain the mean mass per bee. This mean mass was used to convert the mass of the bee population into a number of bees (Farrar 1937, Chabert et al. 2021). The areas of unsealed and sealed brood, and of pollen and honey stores were assessed for each colony by placing a clear acrylic plexiglass sheet on each frame side and by drawing the outline of each component with a marker. The drawn areas were then analyzed with the plugin *Versatile Wand Tool* (https://imagej.nih.gov/ij/plugins/versatile-wand-tool/index.html) of the software ImageJ (Schneider et al. 2012). The colony features are given in Supplementary Table S2.

These features enabled us to calculate that the amount of 1 kg of pollen used for the pollen supplementation treatments (see below) was large enough to exceed the homeostatic set point beyond which the colonies decrease their pollen collection: 1 kg of pollen was equivalent to more than 3 wk of pollen consumption of the colony presenting the highest daily pollen consumption, while a honey bee

<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Variation of the flower number (mean ± SE) assessed in 4 plots 2 m long per tunnel per sampling day before (5 sampling days) and after (3 sampling days) colony treatment. The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. #: indicates weak statistical evidence of the interaction between the colony treatment (control versus pollen supplementation) and the period before/after treatment, i.e., with $0.05 \le P < 0.1$ (Table 1).</figcaption></figure>
colony usually maintains a sufficient pollen reserve to meet its needs for about 10 days only (Seeley 1995; see Supplementary material, Section 2 for the calculations).

Following this assessment, each colony out of the 3 within a repetition was treated randomly as follows: 1 colony did not receive any pollen supplementation (= control), 1 colony received a supplementation of 1 kg of pollen in the form of bee pollen pellets inserted in the combs (Fig. 1; Supplementary Material, Section 2), and 1 colony received a supplementation of 1 kg of pollen in the form of a paste laid on top of the hive frames (Fig. 2; Supplementary Material, Section 2). Therefore, there were 5 sampling days before colony treatment for the 2 repetitions (28 and 30 April, 2, 4, and 6 May for repetition 1; 13, 15, 17, 19, and 21 May for repetition 2), and 3 sampling days after colony treatment (8, 10, and 12 May for repetition 1; 23, 25, and 27 May for repetition 2).

## Analysis of the Stigmatic Pollen Loads and Recording of the Resulting Yields

On each sampling day, 14 pistillate flowers were randomly chosen per tunnel in plots evenly distributed in each row. To have a complete uniform distribution of samplings, each plot was sampled every 2 sampling days (see Supplementary Fig. S4). Thus, every 2 sampling days, each plot was sampled once, with 1 pistillate flower sampled on 1 plant. Each time a plot was sampled, a different plant was used. The flowers were labeled with the date and their location identified with a small flag. The stigmas were collected 10 days later not to interfere with the fertilization process. All the pollen grains stay on the stigma during this time interval due to a high adhesion force (Ito and Gorb 2019). These stigmas were individually stored in 1.5 ml plastic tubes and dried for 24 h at 30 °C in a ventilated incubator. To accurately count the number of melon pollen grains deposited on the stigmas, the pollen grains were extracted by sonication in a solution of saline water and malachite green (Vaissière 1991, Vaissière and Froissart 1996), and the resulting pollen suspensions were filtered on white nylon membrane (see Supplementary Material, Section 3). The pollen grains stained with malachite green were then counted

by image analysis with the software ImageJ (see Supplementary Material, Section 3).

To relate the stigmatic pollen loads to the resulting yields, each fruit produced from a flower from which the stigma was sampled was harvested at maturity, weighed and dissected to remove the seeds. The filled seeds were separated from the empty hulls, before being dried and counted for each fruit with a seed counter (Contador; Pfeuffer, Germany). The fruit set, i.e., the % of pistillate flowers setting a fruit, was also recorded.

## Data Analyses

We tested first if there was a difference in the numbers of pistillate and staminate flowers between the 3 colony treatments, as it could have interfered with the effects of the colony treatments on pollination. The numbers of pistillate and staminate flowers counted on each sampling day in the 4 rows of each tunnel were analyzed by grouping the 2 repetitions with generalized linear mixed effect models (GLMMs) with Poisson regression, after checking that there was no overdispersion (i.e., with the dispersion parameter $\Phi$ close to 1; Zuur et al. 2009). The % of staminate flowers per tunnel and per day was analyzed with a GLMM with binomial regression. For each model, the colony treatment (control colony, colony supplemented with pollen pellets in the combs, or colony supplemented with pollen paste) and the experimental period (before or after colony treatment) were set as fixed explanatory variables with an interaction term, and the tunnel and sampling date were set as random effects.

To test if the colony treatment impacted pollen foraging, the number of pollen foragers counted on 200 flowers each day in each tunnel was analyzed by grouping the 2 repetitions with a GLMM with Poisson regression, after checking the absence of overdispersion as well. The % of pollen foragers per tunnel per day was analyzed with a GLMM with binomial regression (success: number of foragers per 200 flowers with pollen in their corbiculae; failure: number of foragers per 200 flowers without pollen in their corbiculae). As before, the colony treatment and the experimental period were set as fixed explanatory variables with an interaction term, and the tunnel and sampling dates were set as random effects.

<table><caption>**Table 2.** Statistics of the GLMMs computed to test the effect of colony treatment on honey bee pollen foraging and pollinating activity</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="5">Number of pollen foragers per 200 flowers</td><td>Intercept: control - BT</td><td>0.781 ± 0.243</td><td>3.22</td><td>0.001</td><td rowspan="5">Moderate</td></tr><tr><td>Control - AT</td><td>0.732 ± 0.344</td><td>2.13</td><td>0.033</td></tr><tr><td>Pollen in the combs - BT</td><td>0.714 ± 0.247</td><td>2.89</td><td>0.004</td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.223 ± 0.272</td><td>0.82</td><td>0.411</td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.788 ± 0.366</td><td>-2.15</td><td><strong>0.031</strong></td></tr><tr><td rowspan="5">% of pollen foragers</td><td>Interaction: pollen paste - AT</td><td>0.082 ± 0.367</td><td>0.22</td><td>0.823</td><td rowspan="5">Weak</td></tr><tr><td>Intercept: control - BT</td><td>-0.436 ± 0.301</td><td>-1.45</td><td>0.148</td></tr><tr><td>Control - AT</td><td>1.209 ± 0.484</td><td>2.50</td><td>0.013</td></tr><tr><td>Pollen in the combs - BT</td><td>0.805 ± 0.365</td><td>2.21</td><td>0.027</td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.116 ± 0.364</td><td>0.32</td><td>0.750</td></tr><tr><td rowspan="5">Number of pollen grains per stigma</td><td>Interaction: pollen in the combs - AT</td><td>-1.080 ± 0.587</td><td>-1.84</td><td>0.066</td><td rowspan="5">Very strong</td></tr><tr><td>Interaction: pollen paste - AT</td><td>0.207 ± 0.597</td><td>0.35</td><td>0.729</td></tr><tr><td>Intercept: control - BT</td><td>8.017 ± 0.083</td><td>96.26</td><td>&lt;0.001</td></tr><tr><td>Control - AT</td><td>-0.205 ± 0.078</td><td>-2.62</td><td>0.009</td></tr><tr><td>Pollen in the combs - BT</td><td>-0.013 ± 0.107</td><td>-0.12</td><td>0.904</td></tr><tr><td rowspan="5"></td><td>Pollen paste on top of the frames - BT</td><td>-0.212 ± 0.107</td><td>-1.98</td><td>0.048</td><td rowspan="5">Moderate</td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>0.590 ± 0.076</td><td>7.77</td><td><strong>&lt;0.001</strong></td></tr><tr><td>Interaction: pollen paste - AT</td><td>0.163 ± 0.075</td><td>2.16</td><td><strong>0.030</strong></td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022). Moderate evidence ($0.01 \le P < 0.05$) is highlighted in italics; very strong evidence ($P < 0.001$) is highlighted in bold.
colony usually maintains a sufficient pollen reserve to meet its needs for about 10 days only (Seeley 1995; see Supplementary material, Section 2 for the calculations).

Following this assessment, each colony out of the 3 within a repetition was treated randomly as follows: 1 colony did not receive any pollen supplementation (= control), 1 colony received a supplementation of 1 kg of pollen in the form of bee pollen pellets inserted in the combs (Fig. 1; Supplementary Material, Section 2), and 1 colony received a supplementation of 1 kg of pollen in the form of a paste laid on top of the hive frames (Fig. 2; Supplementary Material, Section 2). Therefore, there were 5 sampling days before colony treatment for the 2 repetitions (28 and 30 April, 2, 4, and 6 May for repetition 1; 13, 15, 17, 19, and 21 May for repetition 2), and 3 sampling days after colony treatment (8, 10, and 12 May for repetition 1; 23, 25, and 27 May for repetition 2).

## Analysis of the Stigmatic Pollen Loads and Recording of the Resulting Yields

On each sampling day, 14 pistillate flowers were randomly chosen per tunnel in plots evenly distributed in each row. To have a complete uniform distribution of samplings, each plot was sampled every 2 sampling days (see Supplementary Fig. S4). Thus, every 2 sampling days, each plot was sampled once, with 1 pistillate flower sampled on 1 plant. Each time a plot was sampled, a different plant was used. The flowers were labeled with the date and their location identified with a small flag. The stigmas were collected 10 days later not to interfere with the fertilization process. All the pollen grains stay on the stigma during this time interval due to a high adhesion force (Ito and Gorb 2019). These stigmas were individually stored in 1.5 ml plastic tubes and dried for 24 h at 30 °C in a ventilated incubator. To accurately count the number of melon pollen grains deposited on the stigmas, the pollen grains were extracted by sonication in a solution of saline water and malachite green (Vaissière 1991, Vaissière and Froissart 1996), and the resulting pollen suspensions were filtered on white nylon membrane (see Supplementary Material, Section 3). The pollen grains stained with malachite green were then counted

by image analysis with the software ImageJ (see Supplementary Material, Section 3).

To relate the stigmatic pollen loads to the resulting yields, each fruit produced from a flower from which the stigma was sampled was harvested at maturity, weighed and dissected to remove the seeds. The filled seeds were separated from the empty hulls, before being dried and counted for each fruit with a seed counter (Contador; Pfeuffer, Germany). The fruit set, i.e., the % of pistillate flowers setting a fruit, was also recorded.

## Data Analyses

We tested first if there was a difference in the numbers of pistillate and staminate flowers between the 3 colony treatments, as it could have interfered with the effects of the colony treatments on pollination. The numbers of pistillate and staminate flowers counted on each sampling day in the 4 rows of each tunnel were analyzed by grouping the 2 repetitions with generalized linear mixed effect models (GLMMs) with Poisson regression, after checking that there was no overdispersion (i.e., with the dispersion parameter $\Phi$ close to 1; Zuur et al. 2009). The % of staminate flowers per tunnel and per day was analyzed with a GLMM with binomial regression. For each model, the colony treatment (control colony, colony supplemented with pollen pellets in the combs, or colony supplemented with pollen paste) and the experimental period (before or after colony treatment) were set as fixed explanatory variables with an interaction term, and the tunnel and sampling date were set as random effects.

To test if the colony treatment impacted pollen foraging, the number of pollen foragers counted on 200 flowers each day in each tunnel was analyzed by grouping the 2 repetitions with a GLMM with Poisson regression, after checking the absence of overdispersion as well. The % of pollen foragers per tunnel per day was analyzed with a GLMM with binomial regression (success: number of foragers per 200 flowers with pollen in their corbiculae; failure: number of foragers per 200 flowers without pollen in their corbiculae). As before, the colony treatment and the experimental period were set as fixed explanatory variables with an interaction term, and the tunnel and sampling dates were set as random effects.

<table><caption>**Table 2.** Statistics of the GLMMs computed to test the effect of colony treatment on honey bee pollen foraging and pollinating activity</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="5">Number of pollen foragers per 200 flowers</td><td>Intercept: control - BT</td><td>0.781 ± 0.243</td><td>3.22</td><td>0.001</td><td rowspan="5">Moderate</td></tr><tr><td>Control - AT</td><td>0.732 ± 0.344</td><td>2.13</td><td>0.033</td></tr><tr><td>Pollen in the combs - BT</td><td>0.714 ± 0.247</td><td>2.89</td><td>0.004</td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.223 ± 0.272</td><td>0.82</td><td>0.411</td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.788 ± 0.366</td><td>-2.15</td><td>0.031</td></tr><tr><td rowspan="5">% of pollen foragers</td><td>Interaction: pollen paste - AT</td><td>0.082 ± 0.367</td><td>0.22</td><td>0.823</td><td rowspan="5">Weak</td></tr><tr><td>Intercept: control - BT</td><td>-0.436 ± 0.301</td><td>-1.45</td><td>0.148</td></tr><tr><td>Control - AT</td><td>1.209 ± 0.484</td><td>2.50</td><td>0.013</td></tr><tr><td>Pollen in the combs - BT</td><td>0.805 ± 0.365</td><td>2.21</td><td>0.027</td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.116 ± 0.364</td><td>0.32</td><td>0.750</td></tr><tr><td rowspan="5">Number of pollen grains per stigma</td><td>Interaction: pollen in the combs - AT</td><td>-1.080 ± 0.587</td><td>-1.84</td><td>0.066</td><td rowspan="5">Very strong</td></tr><tr><td>Interaction: pollen paste - AT</td><td>0.207 ± 0.597</td><td>0.35</td><td>0.729</td></tr><tr><td>Intercept: control - BT</td><td>8.017 ± 0.083</td><td>96.26</td><td>&lt;0.001</td></tr><tr><td>Control - AT</td><td>-0.205 ± 0.078</td><td>-2.62</td><td>0.009</td></tr><tr><td>Pollen in the combs - BT</td><td>-0.013 ± 0.107</td><td>-0.12</td><td>0.904</td></tr><tr><td rowspan="5"></td><td>Pollen paste on top of the frames - BT</td><td>-0.212 ± 0.107</td><td>-1.98</td><td>0.048</td><td rowspan="5">Moderate</td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>0.590 ± 0.076</td><td>7.77</td><td>&lt;0.001</td></tr><tr><td>Interaction: pollen paste - AT</td><td>0.163 ± 0.075</td><td>2.16</td><td>0.030</td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022). Moderate evidence ($0.01 \le P < 0.05$) is highlighted in italics; very strong evidence ($P < 0.001$) is highlighted in bold.
To test if the colony treatment impacted the pollination of pistillate flowers, the number of pollen grains per stigma was analyzed by grouping the 2 repetitions with a GLMM, using the quadratic negative binomial regression (NB2; Hilbe 2014) for the residual distribution, because the number of pollen grains per stigma is a nonindependent count (pollen grains are grouped within stigmas) implying overdispersion. As before, the colony treatment and the experimental period were set as fixed explanatory variables with an interaction term, while the tunnel and sampling date were set as random effects.

In addition, to test a potential effect of temporal dynamics of colony treatment on the pollen foraging and pollination activities of honey bees after treatment, the same models described above were run again but by individually comparing each of the 3 sampling dates after treatment (2, 4, and 6 days after treatment) with the average of the 5 sampling dates before treatment.

Finally, to test if the colony treatment impacted melon production, the fruit set was analyzed with a GLMM with binomial regression. The number of filled seeds per fruit being a nonindependent count (seeds are grouped within fruits) implying overdispersion, it was analyzed with a GLMM with NB2 regression. Fruit mass was analyzed with a linear mixed effect model (LMM). As before, the colony treatment and the experimental period were set as fixed explanatory variables with an interaction term, while the tunnel and sampling date were set as random effects.

Since the initial conditions could not necessarily be the same between the tunnels and the colonies between treatments, we applied a Before-After-Control-Impact (BACI) design (Christie et al. 2019, 2020): the impact of the colony treatments on each dependent variable was analyzed by comparing the variations over time before/after treatment of the dependent variables of the treated colonies with the variations of the control colonies through the interaction terms. BACI designs are robust, even when the initial conditions are not the same between the control and treated sites (Christie et al. 2019). To address the issue of a potential high temporal variability of bee foraging and pollinating activity between days, samplings were repeated simultaneously over several days before and after treatment (5 days before treatment and 3 days after): in this sense, this design was a BACI Paired-Series design (BACIPS; Christie et al. 2019). BACI designs are quite robust to detect the true direction of an effect, even when the number of repetitions is low, such as in our study which included 2 repetitions (Christie et al. 2019). In addition, 645 stigmas were analyzed in total over the 2 repetitions and the 3 colony treatments.

The statistics were computed with the software R, version 4.0.3 (R Core Team 2020). The mixed-effects models were computed with the package *lme4*, version 1.1-31 (Bates et al. 2015). The *P*-values of the LMMs were obtained with the package *lmerTest*, version 3.1-3 (Kuznetsova et al. 2017). The NB2 regression was used with the package *MASS*, version 7.3-58.2 (Venables and Ripley 2002). The gradual language of evidence was chosen to describe the results, following the recommendations of Muff et al. (2022): weak statistical evidence when $0.05 \le P < 0.1$, moderate when $0.01 \le P < 0.05$, strong when $0.001 \le P < 0.01$, and very strong when $P < 0.001$. All the ± errors given around the means in the result section are standard errors.

## Results

Six days after pollen supplementations, all the pollen pellets added into the combs had been packed into bee bread and partly consumed (Fig. 1D), and the pollen paste laid on top of the hive frames had been partly consumed as well (Fig. 2E).

## Flower Density

Over the 2 repetitions, there was no evidence that the number of pistillate and staminate flowers, as well as the % of staminate flowers, per 8 m transect per tunnel per sampling day varied differently before

<figure><img src="image_5.png" /><figcaption>Fig. 4. Variation of the honey bee pollen foraging activity (A, B) assessed around 08:00 UTC (10 AM), and of the honey bee pollinating activity (C), assessed before (5 sampling days) and after (3 sampling days) colony treatment (mean ± SE). The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. Symbols indicate the level of statistical evidence of the interaction between the colony treatment (control versus pollen supplementation) and the period before/after treatment: very strong for *** (*P* < 0.001), moderate for * (0.01 ≤ *P* < 0.05), weak for # (0.05 ≤ *P* < 0.1) (Table 2).</figcaption></figure>
To test if the colony treatment impacted the pollination of pistillate flowers, the number of pollen grains per stigma was analyzed by grouping the 2 repetitions with a GLMM, using the quadratic negative binomial regression (NB2; Hilbe 2014) for the residual distribution, because the number of pollen grains per stigma is a nonindependent count (pollen grains are grouped within stigmas) implying overdispersion. As before, the colony treatment and the experimental period were set as fixed explanatory variables with an interaction term, while the tunnel and sampling date were set as random effects.

In addition, to test a potential effect of temporal dynamics of colony treatment on the pollen foraging and pollination activities of honey bees after treatment, the same models described above were run again but by individually comparing each of the 3 sampling dates after treatment (2, 4, and 6 days after treatment) with the average of the 5 sampling dates before treatment.

Finally, to test if the colony treatment impacted melon production, the fruit set was analyzed with a GLMM with binomial regression. The number of filled seeds per fruit being a nonindependent count (seeds are grouped within fruits) implying overdispersion, it was analyzed with a GLMM with NB2 regression. Fruit mass was analyzed with a linear mixed effect model (LMM). As before, the colony treatment and the experimental period were set as fixed explanatory variables with an interaction term, while the tunnel and sampling date were set as random effects.

Since the initial conditions could not necessarily be the same between the tunnels and the colonies between treatments, we applied a Before-After-Control-Impact (BACI) design (Christie et al. 2019, 2020): the impact of the colony treatments on each dependent variable was analyzed by comparing the variations over time before/after treatment of the dependent variables of the treated colonies with the variations of the control colonies through the interaction terms. BACI designs are robust, even when the initial conditions are not the same between the control and treated sites (Christie et al. 2019). To address the issue of a potential high temporal variability of bee foraging and pollinating activity between days, samplings were repeated simultaneously over several days before and after treatment (5 days before treatment and 3 days after): in this sense, this design was a BACI Paired-Series design (BACIPS; Christie et al. 2019). BACI designs are quite robust to detect the true direction of an effect, even when the number of repetitions is low, such as in our study which included 2 repetitions (Christie et al. 2019). In addition, 645 stigmas were analyzed in total over the 2 repetitions and the 3 colony treatments.

The statistics were computed with the software R, version 4.0.3 (R Core Team 2020). The mixed-effects models were computed with the package *lme4*, version 1.1-31 (Bates et al. 2015). The *P*-values of the LMMs were obtained with the package *lmerTest*, version 3.1-3 (Kuznetsova et al. 2017). The NB2 regression was used with the package *MASS*, version 7.3-58.2 (Venables and Ripley 2002). The gradual language of evidence was chosen to describe the results, following the recommendations of Muff et al. (2022): weak statistical evidence when $0.05 \le P < 0.1$, moderate when $0.01 \le P < 0.05$, strong when $0.001 \le P < 0.01$, and very strong when $P < 0.001$. All the ± errors given around the means in the result section are standard errors.

## Results

Six days after pollen supplementations, all the pollen pellets added into the combs had been packed into bee bread and partly consumed (Fig. 1D), and the pollen paste laid on top of the hive frames had been partly consumed as well (Fig. 2E).

<caption>### Flower Density</caption>

Over the 2 repetitions, there was no evidence that the number of pistillate and staminate flowers, as well as the % of staminate flowers, per 8 m transect per tunnel per sampling day varied differently before

<figure><img src="image_5.png" /><figcaption>Before / after colony treatment</figcaption></figure>

Fig. 4. Variation of the honey bee pollen foraging activity (A, B) assessed around 08:00 UTC (10 AM), and of the honey bee pollinating activity (C), assessed before (5 sampling days) and after (3 sampling days) colony treatment (mean ± SE). The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. Symbols indicate the level of statistical evidence of the interaction between the colony treatment (control versus pollen supplementation) and the period before/after treatment: very strong for *** (*P* < 0.001), moderate for * (0.01 ≤ *P* < 0.05), weak for # (0.05 ≤ *P* < 0.1) (Table 2).
and after colony treatment, for the tunnels supplemented with pollen compared to the control tunnel (P > 0.3 for the interactions; Table 1 and Fig. 3). There was only weak evidence that the number of staminate flowers decreased after treatment in the tunnels supplemented with pollen paste (interaction: z = -1.7, P = 0.09; Fig. 3B) compared to the control tunnels for which there was no evidence of decrease (z = -1.3, P = 0.19).

## Density of Honey Bee Pollen Foragers

As honey bees foraged for pollen almost exclusively in the morning (Supplementary Fig. S5), the analyses of pollen foragers focused on the counts made around 08:00 UTC (10 AM). Over the 2 repetitions, the number of pollen foragers decreased with moderate evidence in the tunnels supplemented with pollen in the combs (interaction: z = -2.2, P = 0.03; Table 2 and Fig. 4A), from 4.9 ± 1.2 pollen foragers per 200 flowers on average before treatment to 4.3 ± 0.6 after treatment, compared to the control tunnels in which this number increased with moderate evidence (z = 2.1, P = 0.03), from 2.4 ± 0.5 pollen foragers before treatment to 4.7 ± 0.8 after treatment. More precisely, the number of pollen foragers decreased with weak evidence to 4.0 (± 1.0 and 0.0, respectively) pollen foragers per 200 flowers in average on the fourth and sixth days after treatment in the tunnels supplemented with pollen in the combs (interactions: z = -1.8, P = 0.08; Table 3 and Fig. 5A), while it increased with weak evidence to 5.0 (± 0.0 and 3.0, respectively) pollen foragers during the same period in the control tunnels (z = 1.7, P = 0.09-0.10). There was no evidence that the number of pollen foragers varied differently on the 2nd day after treatment in the tunnels supplemented with pollen in the combs compared to the control tunnels (interaction: z = -0.9, P = 0.36). On the other hand, there was no evidence that the number of pollen foragers varied differently before and after colony treatment for the tunnels supplemented with pollen paste compared to the control tunnels (P > 0.7 for the interactions; Tables 2 and 3, Figs. 4A and 5A).

There was weak evidence that the % of pollen foragers increased less in the tunnels supplemented with pollen in the combs (interaction: z = -1.8, P = 0.07; Table 2 and Fig. 4B), from 52.7% ± 9.7 on average before treatment to 63.7% ± 4.7 after treatment, compared to the control tunnels in which this % increased with moderate evidence, from 49.0% ± 10.6 before treatment to 74.8% ± 8.9 after treatment (z = 2.5, P = 0.01). More precisely, there was weak evidence that the % of pollen foragers increased less on the sixth day after treatment in the tunnels supplemented with pollen in the combs compared to the control tunnels (interaction: z = -1.8, P = 0.07; Table 3 and Fig. 5B): it reached 55.6% ± 11.1 on average in the tunnels supplemented with pollen in the combs on the sixth day after treatment while it reached 80.8% ± 19.2 in the control tunnels (z = 2.0, P = 0.05). There was no evidence that the % of pollen foragers varied differently on the 2nd and 4th days after treatment in the tunnels supplemented with pollen in the combs compared to the control tunnels (interactions: P > 0.2). On the other hand, there was no evidence that the % of pollen foragers varied differently before and after colony treatment for the tunnels supplemented with pollen paste compared to the control tunnels (P > 0.7 for the interactions; Tables 2 and 3, Figs. 4B and 5B).

## Stigmatic Pollen Loads

While the stigmatic pollen load decreased in the control tunnels with strong evidence over the 2 repetitions (z = -2.6, P = 0.009; Table 2 and Fig. 4C), from 3,069 ± 97 pollen grains on average per stigma before treatment to 2,479 ± 107 after treatment, it increased with very strong evidence, from 3,014 ± 94 before treatment to 4,614 ± 237

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Variation (mean ± SE) over time after colony treatment of the honey bee pollen foraging activity (A, B) assessed around 08:00 UTC (10 AM), and of the honey bee pollinating activity (C). The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. The gray areas correspond to the averages of the 5 dates sampled before treatment across the 2 tunnels for each treatment. Symbols indicate the level of statistical evidence of the interaction between the colony treatment (control versus pollen supplementation) and the period before/after treatment: very strong for *** (P < 0.001), moderate for * (0.01 ≤ P < 0.05), weak for # (0.05 ≤ P < 0.1) (Table 3).</figcaption></figure>

after treatment, i.e., a 1.5-fold increase, in the tunnel supplemented with pollen in the combs (interaction: z = 7.8, P < 0.001). More precisely, the stigmatic pollen load increased in the tunnel supplemented
and after colony treatment, for the tunnels supplemented with pollen compared to the control tunnel (P > 0.3 for the interactions; Table 1 and Fig. 3). There was only weak evidence that the number of staminate flowers decreased after treatment in the tunnels supplemented with pollen paste (interaction: z = -1.7, P = 0.09; Fig. 3B) compared to the control tunnels for which there was no evidence of decrease (z = -1.3, P = 0.19).

## Density of Honey Bee Pollen Foragers

As honey bees foraged for pollen almost exclusively in the morning (Supplementary Fig. S5), the analyses of pollen foragers focused on the counts made around 08:00 UTC (10 AM). Over the 2 repetitions, the number of pollen foragers decreased with moderate evidence in the tunnels supplemented with pollen in the combs (interaction: z = -2.2, P = 0.03; Table 2 and Fig. 4A), from 4.9 ± 1.2 pollen foragers per 200 flowers on average before treatment to 4.3 ± 0.6 after treatment, compared to the control tunnels in which this number increased with moderate evidence (z = 2.1, P = 0.03), from 2.4 ± 0.5 pollen foragers before treatment to 4.7 ± 0.8 after treatment. More precisely, the number of pollen foragers decreased with weak evidence to 4.0 (± 1.0 and 0.0, respectively) pollen foragers per 200 flowers in average on the fourth and sixth days after treatment in the tunnels supplemented with pollen in the combs (interactions: z = -1.8, P = 0.08; Table 3 and Fig. 5A), while it increased with weak evidence to 5.0 (± 0.0 and 3.0, respectively) pollen foragers during the same period in the control tunnels (z = 1.7, P = 0.09-0.10). There was no evidence that the number of pollen foragers varied differently on the 2nd day after treatment in the tunnels supplemented with pollen in the combs compared to the control tunnels (interaction: z = -0.9, P = 0.36). On the other hand, there was no evidence that the number of pollen foragers varied differently before and after colony treatment for the tunnels supplemented with pollen paste compared to the control tunnels (P > 0.7 for the interactions; Tables 2 and 3, Figs. 4A and 5A).

There was weak evidence that the % of pollen foragers increased less in the tunnels supplemented with pollen in the combs (interaction: z = -1.8, P = 0.07; Table 2 and Fig. 4B), from 52.7% ± 9.7 on average before treatment to 63.7% ± 4.7 after treatment, compared to the control tunnels in which this % increased with moderate evidence, from 49.0% ± 10.6 before treatment to 74.8% ± 8.9 after treatment (z = 2.5, P = 0.01). More precisely, there was weak evidence that the % of pollen foragers increased less on the sixth day after treatment in the tunnels supplemented with pollen in the combs compared to the control tunnels (interaction: z = -1.8, P = 0.07; Table 3 and Fig. 5B): it reached 55.6% ± 11.1 on average in the tunnels supplemented with pollen in the combs on the sixth day after treatment while it reached 80.8% ± 19.2 in the control tunnels (z = 2.0, P = 0.05). There was no evidence that the % of pollen foragers varied differently on the 2nd and 4th days after treatment in the tunnels supplemented with pollen in the combs compared to the control tunnels (interactions: P > 0.2). On the other hand, there was no evidence that the % of pollen foragers varied differently before and after colony treatment for the tunnels supplemented with pollen paste compared to the control tunnels (P > 0.7 for the interactions; Tables 2 and 3, Figs. 4B and 5B).

## Stigmatic Pollen Loads

While the stigmatic pollen load decreased in the control tunnels with strong evidence over the 2 repetitions (z = -2.6, P = 0.009; Table 2 and Fig. 4C), from 3,069 ± 97 pollen grains on average per stigma before treatment to 2,479 ± 107 after treatment, it increased with very strong evidence, from 3,014 ± 94 before treatment to 4,614 ± 237

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Variation (mean ± SE) over time after colony treatment of the honey bee pollen foraging activity (A, B) assessed around 08:00 UTC (10 AM), and of the honey bee pollinating activity (C). The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. The gray areas correspond to the averages of the 5 dates sampled before treatment across the 2 tunnels for each treatment. Symbols indicate the level of statistical evidence of the interaction between the colony treatment (control versus pollen supplementation) and the period before/after treatment: very strong for *** (P < 0.001), moderate for * (0.01 ≤ P < 0.05), weak for # (0.05 ≤ P < 0.1) (Table 3).</figcaption></figure>

after treatment, i.e., a 1.5-fold increase, in the tunnel supplemented with pollen in the combs (interaction: z = 7.8, P < 0.001). More precisely, the stigmatic pollen load increased in the tunnel supplemented
<table><caption>**Table 3.** Statistics of the GLMMs computed to test the effect of colony treatment on honey bee pollen foraging and pollinating activity, testing independently each sampling date after colony treatment in comparison with the average of the sampling dates before treatment</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="10">Number of pollen foragers per 200 flowers</td><td>Intercept: control - BT</td><td>0.781 ± 0.242</td><td>3.22</td><td>0.001</td><td></td></tr><tr><td>Control - 2 days AT</td><td>0.579 ± 0.504</td><td>1.15</td><td>0.251</td><td></td></tr><tr><td>Control - 4 days AT</td><td>0.796 ± 0.479</td><td>1.66</td><td>0.097</td><td></td></tr><tr><td>Control - 6 days AT</td><td>0.808 ± 0.479</td><td>1.69</td><td>0.092</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.715 ± 0.247</td><td>2.89</td><td>0.004</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.224 ± 0.272</td><td>0.83</td><td>0.409</td><td></td></tr><tr><td>Interaction: pollen in the combs - 2 days AT</td><td>-0.491 ± 0.532</td><td>-0.92</td><td>0.355</td><td rowspan="2">Weak</td></tr><tr><td>Interaction: pollen in the combs - 4 days AT</td><td>-0.938 ± 0.532</td><td>-1.76</td><td>0.078</td></tr><tr><td>Interaction: pollen in the combs - 6 days AT</td><td>-0.938 ± 0.532</td><td>-1.76</td><td>0.078</td><td rowspan="2">Weak</td></tr><tr><td>Interaction: pollen paste - 2 days AT</td><td>0.095 ± 0.535</td><td>0.18</td><td>0.859</td></tr><tr><td>Interaction: pollen paste - 4 days AT</td><td>-0.042 ± 0.504</td><td>-0.08</td><td>0.934</td><td></td></tr><tr><td>Interaction: pollen paste - 6 days AT</td><td>0.181 ± 0.488</td><td>0.37</td><td>0.710</td><td></td></tr><tr><td rowspan="10">% of pollen foragers</td><td>Intercept: control - BT</td><td>-0.361 ± 0.367</td><td>-0.99</td><td>0.324</td><td></td></tr><tr><td>Control - 2 days AT</td><td>1.152 ± 0.709</td><td>1.62</td><td>0.104</td><td></td></tr><tr><td>Control - 4 days AT</td><td>1.199 ± 0.652</td><td>1.84</td><td>0.066</td><td></td></tr><tr><td>Control - 6 days AT</td><td>1.318 ± 0.672</td><td>1.96</td><td>0.050</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.782 ± 0.475</td><td>1.65</td><td>0.100</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.075 ± 0.478</td><td>0.16</td><td>0.875</td><td></td></tr><tr><td>Interaction: pollen in the combs - 2 days AT</td><td>-0.942 ± 0.896</td><td>-1.05</td><td>0.293</td><td rowspan="2">Weak</td></tr><tr><td>Interaction: pollen in the combs - 4 days AT</td><td>-0.846 ± 0.911</td><td>-0.93</td><td>0.353</td></tr><tr><td>Interaction: pollen in the combs - 6 days AT</td><td>-1.567 ± 0.866</td><td>-1.81</td><td>0.071</td><td></td></tr><tr><td>Interaction: pollen paste - 2 days AT</td><td>0.189 ± 0.935</td><td>0.20</td><td>0.839</td><td></td></tr><tr><td>Interaction: pollen paste - 4 days AT</td><td>0.260 ± 0.886</td><td>0.29</td><td>0.769</td><td></td></tr><tr><td>Interaction: pollen paste - 6 days AT</td><td>0.005 ± 0.901</td><td>0.01</td><td>0.995</td><td></td></tr><tr><td rowspan="10">Number of pollen grains per stigma</td><td>Intercept: control - BT</td><td>8.017 ± 0.083</td><td>96.82</td><td>&lt; 0.001</td><td></td></tr><tr><td>Control - 2 days AT</td><td>-0.254 ± 0.115</td><td>-2.21</td><td>0.027</td><td></td></tr><tr><td>Control - 4 days AT</td><td>-0.137 ± 0.113</td><td>-1.22</td><td>0.224</td><td></td></tr><tr><td>Control - 6 days AT</td><td>-0.233 ± 0.115</td><td>-2.02</td><td>0.043</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>-0.013 ± 0.107</td><td>-0.12</td><td>0.903</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-0.212 ± 0.107</td><td>-1.97</td><td>0.049</td><td></td></tr><tr><td>Interaction: pollen in the combs - 2 days AT</td><td>0.492 ± 0.113</td><td>4.34</td><td>&lt;0.001</td><td rowspan="2">Very strong</td></tr><tr><td>Interaction: pollen in the combs - 4 days AT</td><td>0.565 ± 0.115</td><td>4.93</td><td>&lt;0.001</td></tr><tr><td>Interaction: pollen in the combs - 6 days AT</td><td>0.719 ± 0.114</td><td>6.32</td><td>&lt;0.001</td><td rowspan="2">Very strong</td></tr><tr><td>Interaction: pollen paste - 2 days AT</td><td>0.164 ± 0.113</td><td>1.45</td><td>0.146</td></tr><tr><td>Interaction: pollen paste - 4 days AT</td><td>0.071 ± 0.112</td><td>0.63</td><td>0.527</td><td></td></tr><tr><td>Interaction: pollen paste - 6 days AT</td><td>0.261 ± 0.114</td><td>2.28</td><td>0.022</td><td>Moderate</td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022). Moderate evidence ($0.01 \le P < 0.05$) is highlighted in italics; very strong evidence ($P \le 0.001$) is highlighted in bold.

with pollen in the combs with very strong evidence to 4,028 ± 382, 4,816 ± 454, and 5,022 ± 390 pollen grains per stigma on the second, fourth, and sixth days after treatment, i.e., a 1.3-, 1.6-, and 1.7-fold increase, respectively, after treatment ($P < 0.001$ for the 3 interactions; Table 3 and Fig. 5C), compared to the control tunnels in which the stigmatic pollen load decreased with moderate evidence on the second and sixth days after treatment ($z = -2.2, P = 0.03$, and $z = -2.0, P = 0.04$, respectively), and without evidence of variation on the fourth day after treatment ($z = -1.2, P = 0.22$).

There was moderate evidence that the stigmatic pollen loads decreased less in the tunnels supplemented with pollen paste (interaction: $z = 2.2, P = 0.03$; Table 2 and Fig. 4C), from 2,482 ± 96 on average before treatment to 2,350 ± 90 after treatment, compared to the control tunnels. More precisely, there was moderate evidence of no decrease of the stigmatic pollen loads in the tunnels supplemented with pollen paste on the sixth day after treatment compared to the control tunnels (interaction: $z = 2.3, P = 0.02$; Table 3 and Fig. 5C), and no evidence of different variation between the tunnels supplemented with pollen paste and the control

tunnel on the second and fourth days after treatment ($P > 0.1$ for the 2 interactions).

## Fruit Set, Seed Set, and Fruit Mass

Over the 2 repetitions, there was no evidence that the fruit set, number of filled seeds per fruit and fruit mass varied differently before and after colony treatment, for the tunnels supplemented with pollen compared to the control tunnel ($P > 0.1$ for the interactions; Table 4 and Fig. 6). There was only moderate evidence that the fruit set decreased after treatment in the tunnels supplemented with pollen paste (interaction: $z = -2.0, P = 0.04$; Fig. 6A), from 23.9% ± 3.7 on average before treatment to 1.2% ± 1.2 after treatment, compared to the control tunnels for which there was no evidence of decrease ($z = -0.9, P = 0.35$). There was also moderate evidence that the number of filled seeds per fruit did not vary after treatment in the tunnels supplemented with pollen in the combs with an average of 607 ± 11 seeds (interaction: $z = 2.4, P = 0.02$; Fig. 6B), compared to the control tunnels for which there was strong evidence of a decrease of the number of filled seeds per fruit ($z = -3.1, P = 0.002$),
<table><caption>**Table 3.** Statistics of the GLMMs computed to test the effect of colony treatment on honey bee pollen foraging and pollinating activity, testing independently each sampling date after colony treatment in comparison with the average of the sampling dates before treatment</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="10">Number of pollen foragers per 200 flowers</td><td>Intercept: control - BT</td><td>0.781 ± 0.242</td><td>3.22</td><td>0.001</td><td></td></tr><tr><td>Control - 2 days AT</td><td>0.579 ± 0.504</td><td>1.15</td><td>0.251</td><td></td></tr><tr><td>Control - 4 days AT</td><td>0.796 ± 0.479</td><td>1.66</td><td>0.097</td><td></td></tr><tr><td>Control - 6 days AT</td><td>0.808 ± 0.479</td><td>1.69</td><td>0.092</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.715 ± 0.247</td><td>2.89</td><td>0.004</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.224 ± 0.272</td><td>0.83</td><td>0.409</td><td></td></tr><tr><td>Interaction: pollen in the combs - 2 days AT</td><td>-0.491 ± 0.532</td><td>-0.92</td><td>0.355</td><td rowspan="2">Weak</td></tr><tr><td>Interaction: pollen in the combs - 4 days AT</td><td>-0.938 ± 0.532</td><td>-1.76</td><td>0.078</td></tr><tr><td>Interaction: pollen in the combs - 6 days AT</td><td>-0.938 ± 0.532</td><td>-1.76</td><td>0.078</td><td rowspan="2">Weak</td></tr><tr><td>Interaction: pollen paste - 2 days AT</td><td>0.095 ± 0.535</td><td>0.18</td><td>0.859</td></tr><tr><td>Interaction: pollen paste - 4 days AT</td><td>-0.042 ± 0.504</td><td>-0.08</td><td>0.934</td><td></td></tr><tr><td>Interaction: pollen paste - 6 days AT</td><td>0.181 ± 0.488</td><td>0.37</td><td>0.710</td><td></td></tr><tr><td rowspan="10">% of pollen foragers</td><td>Intercept: control - BT</td><td>-0.361 ± 0.367</td><td>-0.99</td><td>0.324</td><td></td></tr><tr><td>Control - 2 days AT</td><td>1.152 ± 0.709</td><td>1.62</td><td>0.104</td><td></td></tr><tr><td>Control - 4 days AT</td><td>1.199 ± 0.652</td><td>1.84</td><td>0.066</td><td></td></tr><tr><td>Control - 6 days AT</td><td>1.318 ± 0.672</td><td>1.96</td><td>0.050</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.782 ± 0.475</td><td>1.65</td><td>0.100</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.075 ± 0.478</td><td>0.16</td><td>0.875</td><td></td></tr><tr><td>Interaction: pollen in the combs - 2 days AT</td><td>-0.942 ± 0.896</td><td>-1.05</td><td>0.293</td><td rowspan="2">Weak</td></tr><tr><td>Interaction: pollen in the combs - 4 days AT</td><td>-0.846 ± 0.911</td><td>-0.93</td><td>0.353</td></tr><tr><td>Interaction: pollen in the combs - 6 days AT</td><td>-1.567 ± 0.866</td><td>-1.81</td><td>0.071</td><td></td></tr><tr><td>Interaction: pollen paste - 2 days AT</td><td>0.189 ± 0.935</td><td>0.20</td><td>0.839</td><td></td></tr><tr><td>Interaction: pollen paste - 4 days AT</td><td>0.260 ± 0.886</td><td>0.29</td><td>0.769</td><td></td></tr><tr><td>Interaction: pollen paste - 6 days AT</td><td>0.005 ± 0.901</td><td>0.01</td><td>0.995</td><td></td></tr><tr><td rowspan="10">Number of pollen grains per stigma</td><td>Intercept: control - BT</td><td>8.017 ± 0.083</td><td>96.82</td><td>&lt; 0.001</td><td></td></tr><tr><td>Control - 2 days AT</td><td>-0.254 ± 0.115</td><td>-2.21</td><td>0.027</td><td></td></tr><tr><td>Control - 4 days AT</td><td>-0.137 ± 0.113</td><td>-1.22</td><td>0.224</td><td></td></tr><tr><td>Control - 6 days AT</td><td>-0.233 ± 0.115</td><td>-2.02</td><td>0.043</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>-0.013 ± 0.107</td><td>-0.12</td><td>0.903</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-0.212 ± 0.107</td><td>-1.97</td><td>0.049</td><td></td></tr><tr><td>Interaction: pollen in the combs - 2 days AT</td><td>0.492 ± 0.113</td><td>4.34</td><td>&lt;0.001</td><td rowspan="2">Very strong</td></tr><tr><td>Interaction: pollen in the combs - 4 days AT</td><td>0.565 ± 0.115</td><td>4.93</td><td>&lt;0.001</td></tr><tr><td>Interaction: pollen in the combs - 6 days AT</td><td>0.719 ± 0.114</td><td>6.32</td><td>&lt;0.001</td><td rowspan="2">Very strong</td></tr><tr><td>Interaction: pollen paste - 2 days AT</td><td>0.164 ± 0.113</td><td>1.45</td><td>0.146</td></tr><tr><td>Interaction: pollen paste - 4 days AT</td><td>0.071 ± 0.112</td><td>0.63</td><td>0.527</td><td></td></tr><tr><td>Interaction: pollen paste - 6 days AT</td><td>0.261 ± 0.114</td><td>2.28</td><td>0.022</td><td>Moderate</td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022). Moderate evidence ($0.01 \le P < 0.05$) is highlighted in italics; very strong evidence ($P \le 0.001$) is highlighted in bold.

with pollen in the combs with very strong evidence to 4,028 ± 382, 4,816 ± 454, and 5,022 ± 390 pollen grains per stigma on the second, fourth, and sixth days after treatment, i.e., a 1.3-, 1.6-, and 1.7-fold increase, respectively, after treatment ($P < 0.001$ for the 3 interactions; Table 3 and Fig. 5C), compared to the control tunnels in which the stigmatic pollen load decreased with moderate evidence on the second and sixth days after treatment ($z = -2.2, P = 0.03$, and $z = -2.0, P = 0.04$, respectively), and without evidence of variation on the fourth day after treatment ($z = -1.2, P = 0.22$).

There was moderate evidence that the stigmatic pollen loads decreased less in the tunnels supplemented with pollen paste (interaction: $z = 2.2, P = 0.03$; Table 2 and Fig. 4C), from 2,482 ± 96 on average before treatment to 2,350 ± 90 after treatment, compared to the control tunnels. More precisely, there was moderate evidence of no decrease of the stigmatic pollen loads in the tunnels supplemented with pollen paste on the sixth day after treatment compared to the control tunnels (interaction: $z = 2.3, P = 0.02$; Table 3 and Fig. 5C), and no evidence of different variation between the tunnels supplemented with pollen paste and the control

tunnel on the second and fourth days after treatment ($P > 0.1$ for the 2 interactions).

## Fruit Set, Seed Set, and Fruit Mass

Over the 2 repetitions, there was no evidence that the fruit set, number of filled seeds per fruit and fruit mass varied differently before and after colony treatment, for the tunnels supplemented with pollen compared to the control tunnel ($P > 0.1$ for the interactions; Table 4 and Fig. 6). There was only moderate evidence that the fruit set decreased after treatment in the tunnels supplemented with pollen paste (interaction: $z = -2.0, P = 0.04$; Fig. 6A), from 23.9% ± 3.7 on average before treatment to 1.2% ± 1.2 after treatment, compared to the control tunnels for which there was no evidence of decrease ($z = -0.9, P = 0.35$). There was also moderate evidence that the number of filled seeds per fruit did not vary after treatment in the tunnels supplemented with pollen in the combs with an average of 607 ± 11 seeds (interaction: $z = 2.4, P = 0.02$; Fig. 6B), compared to the control tunnels for which there was strong evidence of a decrease of the number of filled seeds per fruit ($z = -3.1, P = 0.002$),
<table><caption>**Table 4.** Statistics of the (G)LMMs computed to test the effect of colony treatment on the 3 yield variables</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z or t</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="6">Fruit set</td><td>Intercept: control - BT</td><td>-2.009 ± 0.543</td><td>-3.70</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-0.857 ± 0.915</td><td>-0.94</td><td>0.349</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.894 ± 0.361</td><td>2.48</td><td>0.013</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.344 ± 0.372</td><td>0.92</td><td>0.356</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.436 ± 0.651</td><td>-0.67</td><td>0.504</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-2.245 ± 1.111</td><td>-2.02</td><td>0.043</td><td>Moderate</td></tr><tr><td rowspan="6">Number of filled seeds per fruit</td><td>Intercept: control - BT</td><td>6.460 ± 0.033</td><td>196.12</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-0.245 ± 0.079</td><td>-3.11</td><td>0.002</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>-0.052 ± 0.043</td><td>-1.22</td><td>0.223</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-0.127 ± 0.045</td><td>-2.82</td><td>0.005</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>0.246 ± 0.102</td><td>2.42</td><td>0.015</td><td>Moderate</td></tr><tr><td>Interaction: pollen paste - AT</td><td>0.296 ± 0.194</td><td>1.52</td><td>0.128</td><td></td></tr><tr><td rowspan="6">Fuit mass (g)</td><td>Intercept: control - BT</td><td>825.8 ± 36.0</td><td>22.96</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-141.9 ± 75.4</td><td>-1.88</td><td>0.065</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>-87.2 ± 36.8</td><td>-2.37</td><td>0.020</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-172.0 ± 39.2</td><td>-4.39</td><td>&lt;0.001</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>123.4 ± 87.7</td><td>1.41</td><td>0.162</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>169.2 ± 169.9</td><td>1.00</td><td>0.322</td><td></td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022). Moderate evidence ($0.01 \le P < 0.05$) is highlighted in italics.

from 639 ± 21 seeds on average before treatment to 500 ± 73 after treatment.

Discussion

Given that there was no evidence of different variations before/after treatment for the number of flowers and the ratio of staminate to pistillate flowers between the 3 treatments, the variations in flower numbers most probably did not interfere with the effects of the colony treatments on the pollinating activity of the honey bees. Our results demonstrated that the pollen supplementation in the combs increased by a factor of 1.5 on average over the 2 repetitions of the number of pollen grains deposited on melon stigmas. This increase was gradual after the pollen supplementation: the stigmatic pollen load first increased by 1.3 two days after the supplementation, and then by 1.6 and 1.7 after 4 and 6 days after the supplementation.

These results are in accordance with our hypothesis that supplementing a honey bee colony with pollen in its combs could increase its pollinating activity through the reduction in pollen foraging and pollen theft in a nectariferous crop with anthers isolated from stigmas. However, we observed only weak to moderate evidence of a decrease in the pollen forager density and the % of pollen foragers following the pollen supplementation in the combs compared to the control, a decrease that was rather pronounced 4–6 days after the supplementation. This observation contrasts with several previous studies that showed that increasing the pollen stores of a colony divided by 1.2–10 its number of pollen foragers or the number of trips per pollen forager and that this effect occurred as soon as the day after treatment (Camazine 1993, Fewell and Bertram 1999, Vaughan and Calderone 2002, Fewell and Page 2000, Janmaat et al. 2000, Weidenmüller and Tautz 2002; see also Rotjan et al. 2002 for the opposite effect with pollen deprivation).

This low evidence of effect was probably due to the very low number of pollen foragers observed in each tunnel on each observation day, with a range between 0 and 11 pollen foragers per 200 flowers. The sampling effort of observing 200 flowers was therefore probably too small given the rarity of the event of observing a bee in a flower during the monitoring. A solution to increase the sample

size of pollen foragers could be to observe more flowers per tunnel on each day or to monitor it over more days. Another solution could be to count pollen foragers directly at the hive entrance or to equip the hives with pollen traps. It would also have been relevant to record the amount of pollen carried by nectar foragers on their bodies to confirm the mechanisms of our hypothesis (for methodology, see for example Vaissière and Froissart 1996, Weinman et al. 2023). At last, it would be interesting for the future to repeat this experiment with more days monitored after the pollen supplementation, to know the duration of the effect after treatment on pollen foraging and at which frequency this treatment should be repeated during the flowering of a crop. Dogterom and Winston (1999) showed for instance that colonies supplemented with pollen in the combs recovered levels of pollen foraging similar to colonies not supplemented 7 days after supplementation.

On the other hand, the pollen supplementation in a paste form laid on top of the hive frames did not increase the number of pollen grains on melon stigmas, nor did it decrease the pollen foraging activity of honey bees either. This result can be explained by the fact that, although pollen pastes and pollen substitutes laid on top of the hive frames are usually used and consumed by honey bee colonies, the pollen pastes and substitutes are not stored in the combs (Noordyke et al. 2021). Yet, when they are back to the nest, honey bee pollen foragers assess the colony pollen stores by the time spent and the numbers of cells inspected to find a cell close to unsealed brood with enough available space to unload their pollen pellets (Dreller and Tarpy 2000, Calderone and Johnson 2002). In this way, pollen stores are assessed by direct contact with pollen cells (Dreller and Tarpy 2000, Vaughan and Calderone 2002), and not by scents emitted by pollen (Camazine 1993, Dreller and Tarpy 2000), nor by information exchanged with nonforaging nestmates such as nurses through trophallaxis or antennal contact (Vaughan and Calderone 2002). Consequently, if the cells around the unsealed brood stay empty, the pollen foragers will continue to assess the pollen stores as low, and thus continue to collect pollen.

Likewise, other studies also showed that pollen or protein pastes laid on top of the hive frames did not decrease the pollen foraging activity of colonies (de Mattos et al. 2015, Lamontagne-Drolet et
<table><caption>**Table 4.** Statistics of the (G)LMMs computed to test the effect of colony treatment on the 3 yield variables</caption><thead><tr><th>Response variable</th><th>Predictor</th><th>Estimate ± SE</th><th>z or t</th><th>P</th><th>Statistical evidence of interactions</th></tr></thead><tbody><tr><td rowspan="6">Fruit set</td><td>Intercept: control - BT</td><td>-2.009 ± 0.543</td><td>-3.70</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-0.857 ± 0.915</td><td>-0.94</td><td>0.349</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>0.894 ± 0.361</td><td>2.48</td><td>0.013</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>0.344 ± 0.372</td><td>0.92</td><td>0.356</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>-0.436 ± 0.651</td><td>-0.67</td><td>0.504</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>-2.245 ± 1.111</td><td>-2.02</td><td>0.043</td><td>Moderate</td></tr><tr><td rowspan="6">Number of filled seeds per fruit</td><td>Intercept: control - BT</td><td>6.460 ± 0.033</td><td>196.12</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-0.245 ± 0.079</td><td>-3.11</td><td>0.002</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>-0.052 ± 0.043</td><td>-1.22</td><td>0.223</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-0.127 ± 0.045</td><td>-2.82</td><td>0.005</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>0.246 ± 0.102</td><td>2.42</td><td>0.015</td><td>Moderate</td></tr><tr><td>Interaction: pollen paste - AT</td><td>0.296 ± 0.194</td><td>1.52</td><td>0.128</td><td></td></tr><tr><td rowspan="6">Fuit mass (g)</td><td>Intercept: control - BT</td><td>825.8 ± 36.0</td><td>22.96</td><td>&lt;0.001</td><td></td></tr><tr><td>Control - AT</td><td>-141.9 ± 75.4</td><td>-1.88</td><td>0.065</td><td></td></tr><tr><td>Pollen in the combs - BT</td><td>-87.2 ± 36.8</td><td>-2.37</td><td>0.020</td><td></td></tr><tr><td>Pollen paste on top of the frames - BT</td><td>-172.0 ± 39.2</td><td>-4.39</td><td>&lt;0.001</td><td></td></tr><tr><td>Interaction: pollen in the combs - AT</td><td>123.4 ± 87.7</td><td>1.41</td><td>0.162</td><td></td></tr><tr><td>Interaction: pollen paste - AT</td><td>169.2 ± 169.9</td><td>1.00</td><td>0.322</td><td></td></tr></tbody></table>

AT, after treatment; BT, before treatment. The rows highlighted in gray correspond to the interaction terms, on which the interpretations are focused to test the hypotheses. Statistical evidence follows recommendations made by Muff et al. (2022). Moderate evidence ($0.01 \le P < 0.05$) is highlighted in italics.

from 639 ± 21 seeds on average before treatment to 500 ± 73 after treatment.

## Discussion

Given that there was no evidence of different variations before/after treatment for the number of flowers and the ratio of staminate to pistillate flowers between the 3 treatments, the variations in flower numbers most probably did not interfere with the effects of the colony treatments on the pollinating activity of the honey bees. Our results demonstrated that the pollen supplementation in the combs increased by a factor of 1.5 on average over the 2 repetitions of the number of pollen grains deposited on melon stigmas. This increase was gradual after the pollen supplementation: the stigmatic pollen load first increased by 1.3 two days after the supplementation, and then by 1.6 and 1.7 after 4 and 6 days after the supplementation.

These results are in accordance with our hypothesis that supplementing a honey bee colony with pollen in its combs could increase its pollinating activity through the reduction in pollen foraging and pollen theft in a nectariferous crop with anthers isolated from stigmas. However, we observed only weak to moderate evidence of a decrease in the pollen forager density and the % of pollen foragers following the pollen supplementation in the combs compared to the control, a decrease that was rather pronounced 4–6 days after the supplementation. This observation contrasts with several previous studies that showed that increasing the pollen stores of a colony divided by 1.2–10 its number of pollen foragers or the number of trips per pollen forager and that this effect occurred as soon as the day after treatment (Camazine 1993, Fewell and Bertram 1999, Vaughan and Calderone 2002, Fewell and Page 2000, Janmaat et al. 2000, Weidenmüller and Tautz 2002; see also Rotjan et al. 2002 for the opposite effect with pollen deprivation).

This low evidence of effect was probably due to the very low number of pollen foragers observed in each tunnel on each observation day, with a range between 0 and 11 pollen foragers per 200 flowers. The sampling effort of observing 200 flowers was therefore probably too small given the rarity of the event of observing a bee in a flower during the monitoring. A solution to increase the sample

size of pollen foragers could be to observe more flowers per tunnel on each day or to monitor it over more days. Another solution could be to count pollen foragers directly at the hive entrance or to equip the hives with pollen traps. It would also have been relevant to record the amount of pollen carried by nectar foragers on their bodies to confirm the mechanisms of our hypothesis (for methodology, see for example Vaissière and Froissart 1996, Weinman et al. 2023). At last, it would be interesting for the future to repeat this experiment with more days monitored after the pollen supplementation, to know the duration of the effect after treatment on pollen foraging and at which frequency this treatment should be repeated during the flowering of a crop. Dogterom and Winston (1999) showed for instance that colonies supplemented with pollen in the combs recovered levels of pollen foraging similar to colonies not supplemented 7 days after supplementation.

On the other hand, the pollen supplementation in a paste form laid on top of the hive frames did not increase the number of pollen grains on melon stigmas, nor did it decrease the pollen foraging activity of honey bees either. This result can be explained by the fact that, although pollen pastes and pollen substitutes laid on top of the hive frames are usually used and consumed by honey bee colonies, the pollen pastes and substitutes are not stored in the combs (Noordyke et al. 2021). Yet, when they are back to the nest, honey bee pollen foragers assess the colony pollen stores by the time spent and the numbers of cells inspected to find a cell close to unsealed brood with enough available space to unload their pollen pellets (Dreller and Tarpy 2000, Calderone and Johnson 2002). In this way, pollen stores are assessed by direct contact with pollen cells (Dreller and Tarpy 2000, Vaughan and Calderone 2002), and not by scents emitted by pollen (Camazine 1993, Dreller and Tarpy 2000), nor by information exchanged with nonforaging nestmates such as nurses through trophallaxis or antennal contact (Vaughan and Calderone 2002). Consequently, if the cells around the unsealed brood stay empty, the pollen foragers will continue to assess the pollen stores as low, and thus continue to collect pollen.

Likewise, other studies also showed that pollen or protein pastes laid on top of the hive frames did not decrease the pollen foraging activity of colonies (de Mattos et al. 2015, Lamontagne-Drolet et
<figure><img src="image_7.png" /><figcaption>**Fig. 6.** Variation of the yield variables (mean ± SE), assessed before (5 sampling days) and after (3 sampling days) colony treatment. The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. *: indicates moderate statistical evidence of the interactions between the colony treatment (control versus pollen supplementation) and the period before/after treatment, i.e., with $0.01 \le P < 0.05$ (Table 4).</figcaption></figure>

al. 2019, Ahmad et al. 2021), nor increase the pollen stores (Doull 1980a, Kalev et al. 2002, Avni et al. 2009; but see Doull 1973, 1980b). In these studies, the colonies may have been monitored in pollen-deficient environments, like Kalev et al. (2002) which was conducted in tunnels which were pollen-poor environments for bees, i.e., an environment similar to that of our study. In such pollen-poor environments, the pollen stores cannot be increased by a sufficient

influx of environmental pollen, this pollen influx being too low to exceed the daily consumption of the pollen stores. However, in pollen-rich environments enabling a colony to have a good supply of environmental pollen, as in the open, we could assume that a colony supplemented with pollen or protein paste on top of its frames might be able to fill a part of its protein needs by consuming the paste, resulting in a decrease in the consumption of its pollen stores, and thus in an increase in its pollen stores. It is probably what happened in Doull (1973, 1980b). The influx of excess pollen into the colony could cause the colony to progressively increase its pollen stores up to the certain homeostatic point at which the colony decreases its pollen foraging activity. As the increase of pollen stores would be gradual, a certain delay period would be expected before the homeostatic point is reached and the colony decreases its pollen foraging activity. It remains to be determined for how long this delay period is necessary before the supplementation of pollen or protein paste on top of the frames decreases the pollen foraging activity of the colony and, if it does, by how much.

Finally, the pollen supplementation in the combs did not increase the fruit set or the fruit mass in our study, except the seed set, while it increased the stigmatic pollen loads. The average seed set we got in our data corresponds to the average number of 500-600 filled seeds found in the literature for well-shaped fruits in open fields or in enclosures (Mann and Robinson 1950, McGregor and Todd 1952, Mann 1953, Iselin et al. 1974, Gaye et al. 1991), and it is above the required minimum of 400 filled seeds to have fruits of marketable size (McGregor and Todd 1952, Bohn and Davis 1964, Fisher and Pomeroy 1989, Vaissière and Froissart 1996). The absence of effect on fruit set and fruit mass was not surprising and could easily be explained by the fact that melon is strongly resource limited, with plants setting into fruits only their first well-pollinated pistillate flowers (Mann and Robinson 1950, Mann 1953, Norden 1985, Valentin et al. 1999, Valentin-Morison et al. 2006, Pitrat 2008). In our study, the pistillate flowers were probably adequately pollinated, even in the control tunnels in which the honey bee colonies were not pollen supplemented. Resource limitation has therefore probably mitigated the positive impact of the increased stigmatic pollen loads resulting from the pollen supplementation in the combs that we observed.

In the end, our study was mainly a proof of concept, and the method of supplementing honey bee colonies with pollen was demonstrated to be relevant for increasing the production and quality of seeds and fruits of melon, and probably of any nectariferous crops displaying anthers isolated from stigmas, whenever such crops present a deficit of seed and fruit production due to pollen limitation. It is also relevant to increase the pollination effectiveness of honey bees, to enable the farmers to decrease their colony stocking rate, thereby saving on input costs, and decreasing (i) the intraspecific competition between colonies for the nectar and pollen resources available in the crop and the environment and (ii) the potential detrimental effects on native flora and entomofauna of importing too many managed colonies at a single location (Geslin et al. 2017b, 2023, Morales et al. 2017, Russo et al. 2021).

To conclude, supplementing honey bee colonies with pollen in the combs can therefore be an effective method for increasing their pollinating activity in nectariferous crops displaying anthers isolated from stigmas. It could be applied to a wide range of crops exhibiting these features, listed in Supplementary Table S1, including for instance avocado, strawberry, Apiaceae, Amaryllidaceae, and Asteraceae seed crops, Cucurbitaceae, and all hybrid seed crops grown with a gynodioecious system of parental lines. This method would be especially effective in pollen-deficient environments such as
<figure><img src="image_7.png" /><figcaption>**Fig. 6.** Variation of the yield variables (mean ± SE), assessed before (5 sampling days) and after (3 sampling days) colony treatment. The control refers to the tunnels provided with colonies not supplemented with pollen. Each treatment was replicated twice over 2 different periods in independent tunnels. *: indicates moderate statistical evidence of the interactions between the colony treatment (control versus pollen supplementation) and the period before/after treatment, i.e., with $0.01 \le P < 0.05$ (Table 4).</figcaption></figure>

al. 2019, Ahmad et al. 2021), nor increase the pollen stores (Doull 1980a, Kalev et al. 2002, Avni et al. 2009; but see Doull 1973, 1980b). In these studies, the colonies may have been monitored in pollen-deficient environments, like Kalev et al. (2002) which was conducted in tunnels which were pollen-poor environments for bees, i.e., an environment similar to that of our study. In such pollen-poor environments, the pollen stores cannot be increased by a sufficient

influx of environmental pollen, this pollen influx being too low to exceed the daily consumption of the pollen stores. However, in pollen-rich environments enabling a colony to have a good supply of environmental pollen, as in the open, we could assume that a colony supplemented with pollen or protein paste on top of its frames might be able to fill a part of its protein needs by consuming the paste, resulting in a decrease in the consumption of its pollen stores, and thus in an increase in its pollen stores. It is probably what happened in Doull (1973, 1980b). The influx of excess pollen into the colony could cause the colony to progressively increase its pollen stores up to the certain homeostatic point at which the colony decreases its pollen foraging activity. As the increase of pollen stores would be gradual, a certain delay period would be expected before the homeostatic point is reached and the colony decreases its pollen foraging activity. It remains to be determined for how long this delay period is necessary before the supplementation of pollen or protein paste on top of the frames decreases the pollen foraging activity of the colony and, if it does, by how much.

Finally, the pollen supplementation in the combs did not increase the fruit set or the fruit mass in our study, except the seed set, while it increased the stigmatic pollen loads. The average seed set we got in our data corresponds to the average number of 500-600 filled seeds found in the literature for well-shaped fruits in open fields or in enclosures (Mann and Robinson 1950, McGregor and Todd 1952, Mann 1953, Iselin et al. 1974, Gaye et al. 1991), and it is above the required minimum of 400 filled seeds to have fruits of marketable size (McGregor and Todd 1952, Bohn and Davis 1964, Fisher and Pomeroy 1989, Vaissière and Froissart 1996). The absence of effect on fruit set and fruit mass was not surprising and could easily be explained by the fact that melon is strongly resource limited, with plants setting into fruits only their first well-pollinated pistillate flowers (Mann and Robinson 1950, Mann 1953, Norden 1985, Valentin et al. 1999, Valentin-Morison et al. 2006, Pitrat 2008). In our study, the pistillate flowers were probably adequately pollinated, even in the control tunnels in which the honey bee colonies were not pollen supplemented. Resource limitation has therefore probably mitigated the positive impact of the increased stigmatic pollen loads resulting from the pollen supplementation in the combs that we observed.

In the end, our study was mainly a proof of concept, and the method of supplementing honey bee colonies with pollen was demonstrated to be relevant for increasing the production and quality of seeds and fruits of melon, and probably of any nectariferous crops displaying anthers isolated from stigmas, whenever such crops present a deficit of seed and fruit production due to pollen limitation. It is also relevant to increase the pollination effectiveness of honey bees, to enable the farmers to decrease their colony stocking rate, thereby saving on input costs, and decreasing (i) the intraspecific competition between colonies for the nectar and pollen resources available in the crop and the environment and (ii) the potential detrimental effects on native flora and entomofauna of importing too many managed colonies at a single location (Geslin et al. 2017b, 2023, Morales et al. 2017, Russo et al. 2021).

To conclude, supplementing honey bee colonies with pollen in the combs can therefore be an effective method for increasing their pollinating activity in nectariferous crops displaying anthers isolated from stigmas. It could be applied to a wide range of crops exhibiting these features, listed in Supplementary Table S1, including for instance avocado, strawberry, Apiaceae, Amaryllidaceae, and Asteraceae seed crops, Cucurbitaceae, and all hybrid seed crops grown with a gynodioecious system of parental lines. This method would be especially effective in pollen-deficient environments such as
enclosures. On the other hand, supplementing colonies with pollen paste or pollen substitute on top of the hive frames might be an easier and faster means of increasing their pollinating activity in the open, by providing the protein supplementation early enough before the onset of bloom of the target crop. But this last assumption remains to be tested, and the amount of time needed to get the expected effect after the protein supplementation remains to be assessed. This concept could be extended to other social bee species managed for crop pollination that also decrease their pollen foraging activity following pollen supplementation such as bumble bees (*Bombus impatiens* Cresson [Hymenoptera: Apidae]; *Kitaoka and Nieh* 2009) and stingless bees (*Melipona subnitida* Ducke [Hymenoptera: Apidae]; *Maia-Silva* et al. 2016).

## Acknowledgments

We thank Dominique Garcin for allowing us to undertake our study in his melon tunnels, as well as Jean-Paul Vermandère for providing us with the honey bee colonies. We are grateful to Gabriel Carré and Stéphanie Petitcunot for their help regarding the protocol to analyze the pollen loads of melon stigmas, as well as to Ingrid Boucaud, Emilie Jouve and Patrice Lhuillier who contributed to preliminary experiments, to Cyril Scomparin who took some of the images used in this manuscript, and to Corinne Chêne who was very helpful for administrative work. We also thank two anonymous reviewers who helped us to greatly improve the manuscript.

## Funding

This work was supported by the European Agricultural Guarantee Fund as part of the French National Apiculture Programme (FranceAgriMer convention number 10-13 R) and by the French National Research Agency (grant number ANR-19-CE20-0023). S.C. was also funded by the National Institute of Food and Agriculture (NIFA) (Specialty Crop Research Initiative grant number 2020-51181-32155) of the United States Department of Agriculture (USDA). The authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest.

## Author Contributions

B.E.V. conceived and oversaw the study, C.P., L.G., P.R., M.H., B.E.V., M.J.B. and N.M. performed the field work, M.J.B. analyzed the fruits, M.J.B., S.C. and G.P. analyzed the stigmas, N.M. set up the image analysis procedure, N.M., M.J.B. and L.G. contributed to preliminary experiments, S.C. analyzed the data and wrote the original draft of the manuscript, B.E.V. reviewed and edited the manuscript. All authors gave final approval for publication.

## Supplementary Material

Supplementary material and raw data are available at *Journal of Economic Entomology* online.

## References

* Ahmad S, Khan KA, Khan SA, Ghramh HA, Gul A. Comparative assessment of various supplementary diets on commercial honey bee (*Apis mellifera*) health and colony performance. PLoS One. 2021;16(10):e0258430.
https://doi.org/10.1371/journal.pone.0258430

* Aizen MA, Arbetman MP, Chacoff NP, Chalcoff VR, Feinsinger P, Garibaldi LA, Harder LD, Morales CL, Sáez A, Vanbergen AJ. Invasive bees and

their impact on agriculture. Adv Ecol Res. 2020;63:49-92.
https://doi.org/10.1016/bs.aecr.2020.08.001

* Aizen MA, Morales CL, Vázquez DP, Garibaldi LA, Sáez A, Harder LD. When mutualism goes bad: density-dependent impacts of introduced bees on plant reproduction. New Phytol. 2014;204(2):322-328.
https://doi.org/10.1111/nph.12924

* Al-Tikrity WS, Benton AW, Risius ML, Clarke WW Jr. The effect of length of stay of a honeybee colony in a crownvetch field on its foraging behaviour. J Apic Res. 1972;11(1):51-57.
https://doi.org/10.1080/00218839.1972.11099699

* Avni D, Dag A, Shafir S. The effect of surface area of pollen patties fed to honey bee (*Apis mellifera*) colonies on their consumption, brood production and honey yields. J Apic Res. 2009;48(1):23-28.
https://doi.org/10.3896/ibra.1.48.1.06

* Bates D, Maechler M, Bolker B, Walker S. Fitting linear mixed-effects models using lme4. J Stat Softw. 2015;67(1):1-48.
https://doi.org/10.1007/BF00166516

* Bohn GW, Davis GN. Insect pollination is necessary for the production of muskmelons (*Cucumis melo* v. *reticulatus*). J Apic Res. 1964;3(1):61-63.
https://doi.org/10.1080/00218839.1964.11100084

* Brittain C, Williams N, Kremen C, Klein AM. Synergistic effects of non-*Apis* bees and honey bees for pollination services. Proc Biol Sci. 2013;280(1754):20122767.
https://doi.org/10.1098/rspb.2012.2767

* Calderone NW, Johnson BR. The within-nest behaviour of honeybee pollen foragers in colonies with a high or low need for pollen. Anim Behav. 2002;63(4):749-758.
https://doi.org/10.1006/anbe.2001.1957

* Camazine S. The regulation of pollen foraging by honey bees: how foragers assess the colony's need for pollen. Behav Ecol Sociobiol. 1993;32(4):265-272.
https://doi.org/10.1007/BF00166516

* Cavigliasso P, Negri P, Viel M, Graziani MM, Challiol C, Bello F, Sáez A. Precision management of pollination services to blueberry crops. Sci Rep. 2021;11(1):20453.
https://doi.org/10.1038/s41598-021-00068-1

* Chabert S, Requier F, Chadoeu J, Guilbaud L, Morison N, Vaissiere BE. Rapid measurement of the adult worker population size in honey bees. Ecol Indic. 2021;122:107313.
https://doi.org/10.1016/j.ecolind.2020.107313

* Christie AP, Abecasis D, Adjeroud M, Alonso JC, Amano T, Anton A, Baldigo BP, Barrientos R, Bicknell JE, Buhl DA, et al. Quantifying and addressing the prevalence and bias of study designs in the environmental and social sciences. Nat Commun. 2020;11(1):6377.
https://doi.org/10.1038/s41467-020-20142-y

* Christie AP, Amano T, Martin PA, Shackelford GE, Simmons BI, Sutherland WJ. Simple study designs in ecology produce inaccurate estimates of biodiversity responses. J Appl Ecol. 2019;56(12):2742-2754.
https://doi.org/10.1111/1365-2664.13499

* Dag A, Eisikowitch D. The influence of hive location on honeybee foraging activity and fruit set in melons grown in plastic greenhouses. Apidologie. 1995;26(6):511-519.
https://doi.org/10.1051/apido:19950608

* Dag A, Eisikowitch D. Ventilation of greenhouses increases honey bee foraging activity on melon, *Cucumis melo*. J Apic Res. 1999;38(3-4):169-175.
https://doi.org/10.1080/00218839.1999.11101007

* de Mattos IM, Souza J. de, Soares AEE. Analysis of the effects of colony population size and feeding supplementation on bee pollen production. J Apic Res. 2015;54(5):411-419.
https://doi.org/10.1080/00218839.2016.1159892

* Dedej S, Delaplane KS. Net energetic advantage drives honey bees (*Apis mellifera* L) to nectar larceny in *Vaccinium ashei* Reade. Behav Ecol Sociobiol. 2005;57(4):398-403.
https://doi.org/10.1007/s00265-004-0852-z

* Delaplane K. Cantaloupe, honeydew, melon, muskmelon. In: Crop Pollination by Bees, Volume 2: Individual Crops and their Bees. CABI; 2023. p. 121-128.
https://doi.org/10.1079/9781786393548.0019

* Dogterom MH, Winston ML. Pollen storage and foraging by honey bees (*Hymenoptera: Apidae*) in highbush blueberries (*Ericaceae*), cultivar Bluecrop. Can Entomol. 1999;131(6):757-768.
https://doi.org/10.4039/ent131757-6

* Doull KM. Relationships between pollen, broodrearing and consumption of pollen supplements by honeybees. Apidologie. 1973;4(4):285-293.
https://doi.org/10.1051/apido:19730401

* Doull KM. Relationships between consumption of a pollen supplement, honey production and broodrearing in colonies of honeybees *Apis*
enclosures. On the other hand, supplementing colonies with pollen paste or pollen substitute on top of the hive frames might be an easier and faster means of increasing their pollinating activity in the open, by providing the protein supplementation early enough before the onset of bloom of the target crop. But this last assumption remains to be tested, and the amount of time needed to get the expected effect after the protein supplementation remains to be assessed. This concept could be extended to other social bee species managed for crop pollination that also decrease their pollen foraging activity following pollen supplementation such as bumble bees (*Bombus impatiens* Cresson [Hymenoptera: Apidae]; *Kitaoka and Nieh* 2009) and stingless bees (*Melipona subnitida* Ducke [Hymenoptera: Apidae]; *Maia-Silva* et al. 2016).

## Acknowledgments

We thank Dominique Garcin for allowing us to undertake our study in his melon tunnels, as well as Jean-Paul Vermandère for providing us with the honey bee colonies. We are grateful to Gabriel Carré and Stéphanie Petitcunot for their help regarding the protocol to analyze the pollen loads of melon stigmas, as well as to Ingrid Boucaud, Emilie Jouve and Patrice Lhuillier who contributed to preliminary experiments, to Cyril Scomparin who took some of the images used in this manuscript, and to Corinne Chêne who was very helpful for administrative work. We also thank two anonymous reviewers who helped us to greatly improve the manuscript.

## Funding

This work was supported by the European Agricultural Guarantee Fund as part of the French National Apiculture Programme (FranceAgriMer convention number 10-13 R) and by the French National Research Agency (grant number ANR-19-CE20-0023). S.C. was also funded by the National Institute of Food and Agriculture (NIFA) (Specialty Crop Research Initiative grant number 2020-51181-32155) of the United States Department of Agriculture (USDA). The authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest.

## Author Contributions

B.E.V. conceived and oversaw the study, C.P., L.G., P.R., M.H., B.E.V., M.J.B. and N.M. performed the field work, M.J.B. analyzed the fruits, M.J.B., S.C. and G.P. analyzed the stigmas, N.M. set up the image analysis procedure, N.M., M.J.B. and L.G. contributed to preliminary experiments, S.C. analyzed the data and wrote the original draft of the manuscript, B.E.V. reviewed and edited the manuscript. All authors gave final approval for publication.

## Supplementary Material

Supplementary material and raw data are available at *Journal of Economic Entomology* online.

## References

* Ahmad S, Khan KA, Khan SA, Ghramh HA, Gul A. Comparative assessment of various supplementary diets on commercial honey bee (*Apis mellifera*) health and colony performance. PLoS One. 2021;16(10):e0258430.
https://doi.org/10.1371/journal.pone.0258430

* Aizen MA, Arbetman MP, Chacoff NP, Chalcoff VR, Feinsinger P, Garibaldi LA, Harder LD, Morales CL, Sáez A, Vanbergen AJ. Invasive bees and

their impact on agriculture. Adv Ecol Res. 2020;63:49-92.
https://doi.org/10.1016/bs.aecr.2020.08.001

* Aizen MA, Morales CL, Vázquez DP, Garibaldi LA, Sáez A, Harder LD. When mutualism goes bad: density-dependent impacts of introduced bees on plant reproduction. New Phytol. 2014;204(2):322-328.
https://doi.org/10.1111/nph.12924

* Al-Tikrity WS, Benton AW, Risius ML, Clarke WW Jr. The effect of length of stay of a honeybee colony in a crownvetch field on its foraging behaviour. J Apic Res. 1972;11(1):51-57.
https://doi.org/10.1080/00218839.1972.11099699

* Avni D, Dag A, Shafir S. The effect of surface area of pollen patties fed to honey bee (*Apis mellifera*) colonies on their consumption, brood production and honey yields. J Apic Res. 2009;48(1):23-28.
https://doi.org/10.3896/ibra.1.48.1.06

* Bates D, Maechler M, Bolker B, Walker S. Fitting linear mixed-effects models using lme4. J Stat Softw. 2015;67(1):1-48.
https://doi.org/10.1007/BF00166516

* Bohn GW, Davis GN. Insect pollination is necessary for the production of muskmelons (*Cucumis melo* v. *reticulatus*). J Apic Res. 1964;3(1):61-63.
https://doi.org/10.1080/00218839.1964.11100084

* Brittain C, Williams N, Kremen C, Klein AM. Synergistic effects of non-*Apis* bees and honey bees for pollination services. Proc Biol Sci. 2013;280(1754):20122767.
https://doi.org/10.1098/rspb.2012.2767

* Calderone NW, Johnson BR. The within-nest behaviour of honeybee pollen foragers in colonies with a high or low need for pollen. Anim Behav. 2002;63(4):749-758.
https://doi.org/10.1006/anbe.2001.1957

* Camazine S. The regulation of pollen foraging by honey bees: how foragers assess the colony's need for pollen. Behav Ecol Sociobiol. 1993;32(4):265-272.
https://doi.org/10.1007/BF00166516

* Cavigliasso P, Negri P, Viel M, Graziani MM, Challiol C, Bello F, Sáez A. Precision management of pollination services to blueberry crops. Sci Rep. 2021;11(1):20453.
https://doi.org/10.1038/s41598-021-00068-1

* Chabert S, Requier F, Chadoeu J, Guilbaud L, Morison N, Vaissiere BE. Rapid measurement of the adult worker population size in honey bees. Ecol Indic. 2021;122:107313.
https://doi.org/10.1016/j.ecolind.2020.107313

* Christie AP, Abecasis D, Adjeroud M, Alonso JC, Amano T, Anton A, Baldigo BP, Barrientos R, Bicknell JE, Buhl DA, et al. Quantifying and addressing the prevalence and bias of study designs in the environmental and social sciences. Nat Commun. 2020;11(1):6377.
https://doi.org/10.1038/s41467-020-20142-y

* Christie AP, Amano T, Martin PA, Shackelford GE, Simmons BI, Sutherland WJ. Simple study designs in ecology produce inaccurate estimates of biodiversity responses. J Appl Ecol. 2019;56(12):2742-2754.
https://doi.org/10.1111/1365-2664.13499

* Dag A, Eisikowitch D. The influence of hive location on honeybee foraging activity and fruit set in melons grown in plastic greenhouses. Apidologie. 1995;26(6):511-519.
https://doi.org/10.1051/apido:19950608

* Dag A, Eisikowitch D. Ventilation of greenhouses increases honey bee foraging activity on melon, *Cucumis melo*. J Apic Res. 1999;38(3-4):169-175.
https://doi.org/10.1080/00218839.1999.11101007

* de Mattos IM, Souza J. de, Soares AEE. Analysis of the effects of colony population size and feeding supplementation on bee pollen production. J Apic Res. 2015;54(5):411-419.
https://doi.org/10.1080/00218839.2016.1159892

* Dedej S, Delaplane KS. Net energetic advantage drives honey bees (*Apis mellifera* L) to nectar larceny in Vaccinium ashei Reade. Behav Ecol Sociobiol. 2005;57(4):398-403.
https://doi.org/10.1007/s00265-004-0852-z

* Delaplane K. Cantaloupe, honeydew, melon, muskmelon. In: Crop Pollination by Bees, Volume 2: Individual Crops and their Bees. CABI; 2023. p. 121-128.
https://doi.org/10.1079/9781786393548.0019

* Dogterom MH, Winston ML. Pollen storage and foraging by honey bees (*Hymenoptera: Apidae*) in highbush blueberries (*Ericaceae*), cultivar Bluecrop. Can Entomol. 1999;131(6):757-768.
https://doi.org/10.4039/ent131757-6

* Doull KM. Relationships between pollen, broodrearing and consumption of pollen supplements by honeybees. Apidologie. 1973;4(4):285-293.
https://doi.org/10.1051/apido:19730401

* Doull KM. Relationships between consumption of a pollen supplement, honey production and broodrearing in colonies of honeybees *Apis*
*mellifera* L. I. Apidologie. 1980a:11(4):361-365. https://doi.org/10.1051/apido:19800404

Doull KM. Relationships between consumption of a pollen supplement, honey production and broodrearing in colonies of honeybees *Apis mellifera* L. II. Apidologie. 1980b:11(4):367-374. https://doi.org/10.1051/apido:19800405

Dreller C, Page RE Jr, Fondrk MK. Regulation of pollen foraging in honeybee colonies: effects of young brood, stored pollen, and empty space. Behav Ecol Sociobiol. 1999:45(3):227-233. https://doi.org/10.1007/s002650050557

Dreller C, Tarpy DR. Perception of the pollen need for foragers in a honeybee colony. Anim Behav. 2000:59(1):91-96. https://doi.org/10.1006/anbe.1999.1303

Eeraerts M, Smagghe G, Meeus I. Bumble bee abundance and richness improves honey bee pollination behaviour in sweet cherry. Basic Appl Ecol. 2020:43:27-33. https://doi.org/10.1016/j.baae.2019.11.004

FAOSTAT. Food and Agriculture Organization of the United Nations Statistics Division. 2023. http://www.fao.org/faostat/en/#home.

Farina WM, Arenas A, Estravis-Barcala MC, Palottini F. Targeted crop pollination by training honey bees: advances and perspectives. Front Bee Sci. 2023:1:1253157. https://doi.org/10.3389/frbee.2023.1253157

Farrar CL. The influence of colony populations on honey production. J Agric Res. 1937:54(12):945-954.

Fewell JH, Bertram SM. Division of labor in a dynamic environment: response by honeybees (*Apis mellifera*) to graded changes in colony pollen stores. Behav Ecol Sociobiol. 1999:46(3):171-179. https://doi.org/10.1007/s002650050607

Fewell JH, Page RE. Genotypic variation in foraging responses to environmental stimuli by honey bees, *Apis mellifera*. Experientia. 1993:49(12):1106-1112. https://doi.org/10.1007/bf01929923

Fewell JH, Page RE. Colony-level selection effects on individual and colony foraging task performance in honeybees, *Apis mellifera* L. Behav Ecol Sociobiol. 2000:48:173-181. https://doi.org/10.1007/s002650000183

Fewell JH, Winston ML. Colony state and regulation of pollen foraging in the honey bee, *Apis mellifera* L. Behav Ecol Sociobiol. 1992:30(6):387-393. https://doi.org/10.1007/BF00176173

Fewell JH, Winston ML. Regulation of nectar collection in relation to honey storage levels by honey bees, *Apis mellifera*. Behav Ecol. 1996:7(3):286-291. https://doi.org/10.1093/beheco/7.3.286

Fisher RM, Pomeroy N. Pollination of greenhouse muskmelons by bumble bees (Hymenoptera: Apidae). J Econ Entomol. 1989:82(4):1061-1066. https://doi.org/10.1093/jee/82.4.1061

Földesi R, Howlett BG, Grass I, Batáry P. Larger pollinators deposit more pollen on stigmas across multiple plant species—a meta-analysis. J Appl Ecol. 2021:58(4):699-707. https://doi.org/10.1111/1365-2664.13798

Gaines-Day HR, Gratton C. Crop yield is correlated with honey bee hive density but not in high-woodland landscapes. Agric Ecosyst Environ. 2016:218:53-57. https://doi.org/10.1016/j.agee.2015.11.001

Garibaldi LA, Carvalheiro LG, Vaissière BE, Gemmill-Herren B, Hipólito J, Freitas BM, Ngo HT, Azza N, Sáez A, Áström J, et al. Mutually beneficial pollinator diversity and crop yield outcomes in small and large farms. Science. 2016:351(6271):388-391. https://doi.org/10.1126/science.aac7287

Garibaldi LA, Steffan-Dewenter I, Winfree R, Aizen MA, Bommarco R, Cunningham SA, Kremen C, Carvalheiro LG, Harder LD, Afik O, et al. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science. 2013:339(6127):1608-1611. https://doi.org/10.1126/science.1230200

Gary NE, Witherell PC, Lorenzen K. A comparison of the foraging activities of common Italian and 'Hy-Queen' honey bees. Environ Entomol. 1978:7(2):228-232. https://doi.org/10.1093/ee/7.2.228

Gaye MM, Maurer AR, Seywerd FM. Honey bees placed under row covers affect muskmelon yield and quality. Sci Hortic. 1991:47(1-2):59-66. https://doi.org/10.1016/0304-4238(91)90027-v

Gemeda TK, Li J, Luo S, Yang H, Jin T, Huang J, Wu J. Pollen trapping and sugar syrup feeding of honey bee (Hymenoptera: Apidae) enhance pollen collection of less preferred flowers. PLoS One. 2018:13(9):e0203648. https://doi.org/10.1371/journal.pone.0203648

Geslin B, Aizen MA, Garcia N, Pereira AJ, Vaissière BE, Garibaldi LA. The impact of honey bee colony quality on crop yield and farmers' profit in apples and pears. Agric Ecosyst Environ. 2017a:248:153-161. https://doi.org/10.1016/j.agee.2017.07.035

Geslin B, Gauzens B, Baude M, Dajoz I, Fontaine C, Henry M, Ropars L, Rollin O, Thébault E, Vereecken NJ. Massively introduced managed species and their consequences for plant-pollinator interactions. Adv Ecol Res. 2017b:57:147-199. https://doi.org/10.1016/bs.aecr.2016.10.007

Geslin B, Mouillard-Lample L, Zakardjian M, Dajoz I, Flacher F, Henry M, Perrard A, Requier F, Ropars L, Schatz B, et al. New insights on massively introduced managed species and their consequences for plant-pollinator interactions. Adv Ecol Res. 2023:68:63-89. https://doi.org/10.1016/bs.aecr.2023.09.003

Goodwin RM. Feeding sugar syrup to honey bee colonies to improve pollination: a review. Bee World. 1997:78(2):56-62. https://doi.org/10.1080/0005772x.1997.11099335

Grewal GS, Sidhu AS. Studies on insect pollination in *Cucumis melo* Linn. In Proceedings of the 2nd International Conference Apiculture in Tropical Climates; Ludhiana, India. New Delhi (India): Punjab Agricultural University; 1983. p. 537-544.

Hargreaves AL, Harder LD, Johnson SD. Consumptive emasculation: the ecological and evolutionary consequences of pollen theft. Biol Rev Camb Philos Soc. 2009:84(2):259-276. https://doi.org/10.1111/j.1469-185X.2008.00074.x

Hargreaves AL, Harder LD, Johnson SD. Native pollen thieves reduce the reproductive success of a hermaphroditic plant, *Aloe maculata*. Ecology. 2010:91(6):1693-1703. https://doi.org/10.1890/09-0792.1

Hargreaves AL, Harder LD, Johnson SD. Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees. Ann Bot (Lond). 2012:109(4):761-772. https://doi.org/10.1093/aob/mcr324

Hilbe, JM. Modeling count data. Cambridge University Press; 2014.

Hoover SE, Ovinge LP, Kearns JD. Consumption of supplemental spring protein feeds by western honey bee (Hymenoptera: Apidae) colonies: effects on colony growth and pollination potential. J Econ Entomol. 2022:115(2):417-429. https://doi.org/10.1093/jee/toac006

Hung KLJ, Kingston JM, Albrecht M, Holway DA, Kohn JR. The worldwide importance of honey bees as pollinators in natural habitats. Proc R Soc B Biol Sci.. 2018:285(1870):20172140. https://doi.org/10.1098/rspb.2017.2140

Isaacs R, Williams N, Ellis J, Pitts-Singer TL, Bommarco R, Vaughan M. Integrated crop pollination: combining strategies to ensure stable and sustainable yields of pollination-dependent crops. Basic Appl Ecol. 2017:22:44-60. https://doi.org/10.1016/j.baae.2017.07.003

Iselin WA, Jensen MH, Spangler HG. The pollination of melons in air inflated greenhouses by honey bees. Environ Entomol. 1974:3(4):664-666. https://doi.org/10.1093/ee/3.4.664

Ish-Am G, Eisikowitch D. The behaviour of honey bees (*Apis mellifera*) visiting avocado (*Persea americana*) flowers and their contribution to its pollination. J Apic Res. 1993:32(3-4):175-186. https://doi.org/10.1080/00218839.1993.11101303

Ito S, Gorb SN. Attachment-based mechanisms underlying capture and release of pollen grains. J R Soc Interface. 2019:16(157):20190269. https://doi.org/10.1098/rsif.2019.0269

Jackson JF. Gene flow in pollen in commercial almond orchards. Sex Plant Reprod. 1996:9(6):367-369. https://doi.org/10.1007/bf02441958

Janmaat AF, Winston ML, Ydenberg RC. Condition-dependent response to changes in pollen stores by honey bee (*Apis mellifera*) colonies with different parasitic loads. Behav Ecol Sociobiol. 2000:47(3):171-179. https://doi.org/10.1007/s002650050008

Jay SC. Spatial management of honey bees on crops. Annu Rev Entomol. 1986:31(1):49-65. https://doi.org/10.1146/annurev.en.31.010186.000405

Junqueira CN, Pereira RAS, da Silva RC, Alves Cardoso Kobal RO, Araújo TN, Prato A, Pedrosa J, Martínez-Martínez CA, Castrillon KP, Felício DT, et al. Do *Apis* and non-*Apis* bees provide a similar contribution to crop production with different levels of pollination dependency? A review using meta-analysis. Ecol Entomol. 2022:47(1):76-83. https://doi.org/10.1111/een.13092
*mellifera* L. I. Apidologie. 1980a:11(4):361-365. https://doi.org/10.1051/apido:19800404

Doull KM. Relationships between consumption of a pollen supplement, honey production and broodrearing in colonies of honeybees *Apis mellifera* L. II. Apidologie. 1980b:11(4):367-374. https://doi.org/10.1051/apido:19800405

Dreller C, Page RE Jr, Fondrk MK. Regulation of pollen foraging in honeybee colonies: effects of young brood, stored pollen, and empty space. Behav Ecol Sociobiol. 1999:45(3):227-233. https://doi.org/10.1007/s002650050557

Dreller C, Tarpy DR. Perception of the pollen need for foragers in a honeybee colony. Anim Behav. 2000:59(1):91-96. https://doi.org/10.1006/anbe.1999.1303

Eeraerts M, Smagghe G, Meeus I. Bumble bee abundance and richness improves honey bee pollination behaviour in sweet cherry. Basic Appl Ecol. 2020:43:27-33. https://doi.org/10.1016/j.baae.2019.11.004

FAOSTAT. Food and Agriculture Organization of the United Nations Statistics Division. 2023. http://www.fao.org/faostat/en/#home.

Farina WM, Arenas A, Estravis-Barcala MC, Palottini F. Targeted crop pollination by training honey bees: advances and perspectives. Front Bee Sci. 2023:1:1253157. https://doi.org/10.3389/frbee.2023.1253157

Farrar CL. The influence of colony populations on honey production. J Agric Res. 1937:54(12):945-954.

Fewell JH, Bertram SM. Division of labor in a dynamic environment: response by honeybees (*Apis mellifera*) to graded changes in colony pollen stores. Behav Ecol Sociobiol. 1999:46(3):171-179. https://doi.org/10.1007/s002650050607

Fewell JH, Page RE. Genotypic variation in foraging responses to environmental stimuli by honey bees, *Apis mellifera*. Experientia. 1993:49(12):1106-1112. https://doi.org/10.1007/bf01929923

Fewell JH, Page RE. Colony-level selection effects on individual and colony foraging task performance in honeybees, *Apis mellifera* L. Behav Ecol Sociobiol. 2000:48:173-181. https://doi.org/10.1007/s002650000183

Fewell JH, Winston ML. Colony state and regulation of pollen foraging in the honey bee, *Apis mellifera* L. Behav Ecol Sociobiol. 1992:30(6):387-393. https://doi.org/10.1007/BF00176173

Fewell JH, Winston ML. Regulation of nectar collection in relation to honey storage levels by honey bees, *Apis mellifera*. Behav Ecol. 1996:7(3):286-291. https://doi.org/10.1093/beheco/7.3.286

Fisher RM, Pomeroy N. Pollination of greenhouse muskmelons by bumble bees (Hymenoptera: Apidae). J Econ Entomol. 1989:82(4):1061-1066. https://doi.org/10.1093/jee/82.4.1061

Földesi R, Howlett BG, Grass I, Batáry P. Larger pollinators deposit more pollen on stigmas across multiple plant species—a meta-analysis. J Appl Ecol. 2021:58(4):699-707. https://doi.org/10.1111/1365-2664.13798

Gaines-Day HR, Gratton C. Crop yield is correlated with honey bee hive density but not in high-woodland landscapes. Agric Ecosyst Environ. 2016:218:53-57. https://doi.org/10.1016/j.agee.2015.11.001

Garibaldi LA, Carvalheiro LG, Vaissière BE, Gemmill-Herren B, Hipólito J, Freitas BM, Ngo HT, Azza N, Sáez A, Áström J, et al. Mutually beneficial pollinator diversity and crop yield outcomes in small and large farms. Science. 2016:351(6271):388-391. https://doi.org/10.1126/science.aac7287

Garibaldi LA, Steffan-Dewenter I, Winfree R, Aizen MA, Bommarco R, Cunningham SA, Kremen C, Carvalheiro LG, Harder LD, Afik O, et al. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science. 2013:339(6127):1608-1611. https://doi.org/10.1126/science.1230200

Gary NE, Witherell PC, Lorenzen K. A comparison of the foraging activities of common Italian and 'Hy-Queen' honey bees. Environ Entomol. 1978:7(2):228-232. https://doi.org/10.1093/ee/7.2.228

Gaye MM, Maurer AR, Seywerd FM. Honey bees placed under row covers affect muskmelon yield and quality. Sci Hortic. 1991:47(1-2):59-66. https://doi.org/10.1016/0304-4238(91)90027-v

Gemeda TK, Li J, Luo S, Yang H, Jin T, Huang J, Wu J. Pollen trapping and sugar syrup feeding of honey bee (Hymenoptera: Apidae) enhance pollen collection of less preferred flowers. PLoS One. 2018:13(9):e0203648. https://doi.org/10.1371/journal.pone.0203648

Geslin B, Aizen MA, Garcia N, Pereira AJ, Vaissière BE, Garibaldi LA. The impact of honey bee colony quality on crop yield and farmers' profit in apples and pears. Agric Ecosyst Environ. 2017a:248:153-161. https://doi.org/10.1016/j.agee.2017.07.035

Geslin B, Gauzens B, Baude M, Dajoz I, Fontaine C, Henry M, Ropars L, Rollin O, Thébault E, Vereecken NJ. Massively introduced managed species and their consequences for plant-pollinator interactions. Adv Ecol Res. 2017b:57:147-199. https://doi.org/10.1016/bs.aecr.2016.10.007

Geslin B, Mouillard-Lample L, Zakardjian M, Dajoz I, Flacher F, Henry M, Perrard A, Requier F, Ropars L, Schatz B, et al. New insights on massively introduced managed species and their consequences for plant-pollinator interactions. Adv Ecol Res. 2023:68:63-89. https://doi.org/10.1016/bs.aecr.2023.09.003

Goodwin RM. Feeding sugar syrup to honey bee colonies to improve pollination: a review. Bee World. 1997:78(2):56-62. https://doi.org/10.1080/0005772x.1997.11099335

Grewal GS, Sidhu AS. Studies on insect pollination in *Cucumis melo* Linn. In Proceedings of the 2nd International Conference Apiculture in Tropical Climates; Ludhiana, India. New Delhi (India): Punjab Agricultural University; 1983. p. 537-544.

Hargreaves AL, Harder LD, Johnson SD. Consumptive emasculation: the ecological and evolutionary consequences of pollen theft. Biol Rev Camb Philos Soc. 2009:84(2):259-276. https://doi.org/10.1111/j.1469-185X.2008.00074.x

Hargreaves AL, Harder LD, Johnson SD. Native pollen thieves reduce the reproductive success of a hermaphroditic plant, *Aloe maculata*. Ecology. 2010:91(6):1693-1703. https://doi.org/10.1890/09-0792.1

Hargreaves AL, Harder LD, Johnson SD. Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees. Ann Bot (Lond). 2012:109(4):761-772. https://doi.org/10.1093/aob/mcr324

Hilbe, JM. Modeling count data. Cambridge University Press; 2014.

Hoover SE, Ovinge LP, Kearns JD. Consumption of supplemental spring protein feeds by western honey bee (Hymenoptera: Apidae) colonies: effects on colony growth and pollination potential. J Econ Entomol. 2022:115(2):417-429. https://doi.org/10.1093/jee/toac006

Hung KLJ, Kingston JM, Albrecht M, Holway DA, Kohn JR. The worldwide importance of honey bees as pollinators in natural habitats. Proc R Soc B Biol Sci.. 2018:285(1870):20172140. https://doi.org/10.1098/rspb.2017.2140

Isaacs R, Williams N, Ellis J, Pitts-Singer TL, Bommarco R, Vaughan M. Integrated crop pollination: combining strategies to ensure stable and sustainable yields of pollination-dependent crops. Basic Appl Ecol. 2017:22:44-60. https://doi.org/10.1016/j.baae.2017.07.003

Iselin WA, Jensen MH, Spangler HG. The pollination of melons in air inflated greenhouses by honey bees. Environ Entomol. 1974:3(4):664-666. https://doi.org/10.1093/ee/3.4.664

Ish-Am G, Eisikowitch D. The behaviour of honey bees (*Apis mellifera*) visiting avocado (*Persea americana*) flowers and their contribution to its pollination. J Apic Res. 1993:32(3-4):175-186. https://doi.org/10.1080/00218839.1993.11101303

Ito S, Gorb SN. Attachment-based mechanisms underlying capture and release of pollen grains. J R Soc Interface. 2019:16(157):20190269. https://doi.org/10.1098/rsif.2019.0269

Jackson JF. Gene flow in pollen in commercial almond orchards. Sex Plant Reprod. 1996:9(6):367-369. https://doi.org/10.1007/bf02441958

Janmaat AF, Winston ML, Ydenberg RC. Condition-dependent response to changes in pollen stores by honey bee (*Apis mellifera*) colonies with different parasitic loads. Behav Ecol Sociobiol. 2000:47(3):171-179. https://doi.org/10.1007/s002650050008

Jay SC. Spatial management of honey bees on crops. Annu Rev Entomol. 1986:31(1):49-65. https://doi.org/10.1146/annurev.en.31.010186.000405

Junqueira CN, Pereira RAS, da Silva RC, Alves Cardoso Kobal RO, Araújo TN, Prato A, Pedrosa J, Martínez-Martínez CA, Castrillon KP, Felício DT, et al. Do *Apis* and non-*Apis* bees provide a similar contribution to crop production with different levels of pollination dependency? A review using meta-analysis. Ecol Entomol. 2022:47(1):76-83. https://doi.org/10.1111/een.13092
Kalev H, Dag A, Shafir S. Feeding pollen supplements to honey bee colonies during pollination of sweet pepper in enclosures. Am Bee J. 2002;142(9):675-679.

Kitaoka TK, Nieh JC. Bumble bee pollen foraging regulation: role of pollen quality, storage levels, and odor. Behav Ecol Sociobiol. 2009;63(4):625-625. https://doi.org/10.1007/s00265-008-0707-0

Klein AM, Vaissiere BE, Cane JH, Steffan-Dewenter I, Cunningham SA, Kremen C, Tscharntke T. Importance of pollinators in changing landscapes for world crops. Proc Biol Sci. 2007;274(1608):303-313. https://doi.org/10.1098/rspb.2006.3721

Koski MH, Ison JL, Padilla A, Pham AQ, Galloway LF. Linking pollinator efficiency to patterns of pollen limitation: small bees exploit the plant-pollinator mutualism. Proc Biol Sci. 2018;285(1880):20180635. https://doi.org/10.1098/rspb.2018.0635

Kouonon LC, Jacquemart AL, Zoro Bi AI, Bertin P, Baudoin JP, Dje Y. Reproductive biology of the andromonoecious *Cucumis melo* subsp. *agrestis* (Cucurbitaceae). Ann Bot (Lond). 2009;104(6):1129-1139. https://doi.org/10.1093/aob/mcp196

Kuznetsova A, Brockhoff PB, Christensen RHB. ImerTest package: tests in linear mixed effects models. J Stat Softw. 2017:82(13):1-26. https://doi.org/10.18637/jss.v082.i13

Lamontagne-Drolet M, Samson-Robert O, Giovenazzo P, Fournier V. The impacts of two protein supplements on commercial honey bee (Apis mellifera L.) colonies. J Apic Res. 2019;58(5):800-813. https://doi.org/10.1080/00218839.2019.1644938

Maia-Silva C, Hrncir M, Imperatriz-Fonseca VL, Schorkopf DLP. Stingless bees (*Melipona subnitida*) adjust brood production rather than foraging activity in response to changes in pollen stores. J Comp Physiol A. 2016;202(9-10):723-732. https://doi.org/10.1007/s00359-016-1095-y

Mann LK. Honey bee activity in relation to pollination and fruit set in the cantaloupe (*Cucumis melo*). Am J Bot. 1953;40(7):545-553. https://doi.org/10.1002/j.1537-2197.1953.tb06518.x

Mann LK, Robinson J. Fertilization, seed development, and fruit growth as related to fruit set in the cantaloupe (*Cucumis melo* L.). Am J Bot. 1950;37(9):685-697. https://doi.org/10.1002/j.1537-2197.1950.tb11058.x

Mayer DF. Sequential introduction of honey bee colonies for pear pollination. Acta Hortic. 1994:367(367):267-269. https://doi.org/10.17660/actahortic.1994.367.35

McGregor SE, Levin MD, Foster RE. Honey bee visitors and fruit set of cantaloups. J Econ Entomol. 1965;58(5):968-970. https://doi.org/10.1093/jee/58.5.968

McGregor SE, Todd FE. Cantaloup production with honey bees. J Econ Entomol. 1952;45(1):43-47. https://doi.org/10.1093/jee/45.1.43

Morales CL, Sáez A, Garibaldi LA, Aizen MA. Disruption of pollination services by invasive pollinator species. In: Vilà M, and Hulme PE, editors. Impact of Biological Invasions on Ecosystem Services. Cham (Switzerland): Springer; 2017.p. 203-220.

Muff S, Nilsen EB, O'Hara RB, Nater CR. Rewriting results sections in the language of evidence. Trends Ecol Evol. 2022;37(3):203-210. https://doi.org/10.1016/j.tree.2021.10.009

Noordyke ER, Ellis JD. Reviewing the efficacy of pollen substitutes as a management tool for improving the health and productivity of western honey bee (*Apis mellifera*) colonies. Front Sustain Food Syst. 2021;5:772897. https://doi.org/10.3389/fsufs.2021.772897

Noordyke ER, Santen E. van Ellis JD. Tracing the fate of pollen substitute patties in Western honey bee (Hymenoptera: Apidae) colonies. J Econ Entomol. 2021;114(4):1421-1430. https://doi.org/10.1093/jee/toab083

Norden BMB. The comparative importance of small carpenter bees (*Ceratina spp.*) and other insects to pollination of muskmelon/cantaloupe (*Cucumis melo* L.) in Maryland [Dissertation]. [College Park (MD)]: University of Maryland; 1985.

Orr N, Eisikowitch D. Interaction between melon (*Cucumis melo*) flowers and honeybees under extreme desert conditions in Israel. Apidologie. 1988;19(1):85-96. https://doi.org/10.1051/apido:19880106

Osterman J, Theodorou P, Radzevičiūtė R, Schnitker P, Paxton RJ. Apple pollination is ensured by wild bees when honey bees are drawn away from orchards by a mass co-flowering crop, oilseed rape. Agric Ecosyst Environ. 2021;315:107383. http://doi.org/10.1016/j.agee.2021.107383

Page ML, Nicholson CC, Brennan RM, Britzman AT, Greer J, Hemberger J, Kahl H, Müller U, Peng Y, Rosenberger NM, et al. A meta-analysis of single visit pollination effectiveness comparing honeybees and other floral visitors. Am J Bot. 2021;108(11):2196-2207. https://doi.org/10.1002/ajb2.1764

Page Jr RE, Waddington KD, Hunt GJ, Fondrk MK. Genetic determinants of honey bee foraging behaviour. Anim Behav. 1995;50(6):1617-1625. https://doi.org/10.1016/0003-3472(95)80015-8

Pankiw T. Brood pheromone regulates foraging activity of honey bees (Hymenoptera: Apidae). J Econ Entomol. 2004;97(3):748-751. https://doi.org/10.1093/jee/97.3.748

Pankiw T, Page RE Jr, Fondrk MK. Brood pheromone stimulates pollen foraging in honey bees (*Apis mellifera*). Behav Ecol Sociobiol. 1998;44:193-198. https://doi.org/10.1007/s002650050531

Park MG, Raguso RA, Losey JE, Danforth BN. Per-visit pollinator performance and regional importance of wild *Bombus* and *Andrena* (*Melandrena*) compared to the managed honey bee in New York apple orchards. Apidologie. 2016;47(2):145-160. https://doi.org/10.1007/s13592-015-0383-9

Parker AJ, Tran JL, Ison JL, Bai JDK, Weis AE, Thomson JD. Pollen packing affects the function of pollen on corbiculate bees but not non-corbiculate bees. Arthropod Plant Interact. 2015;9(2):197-203. https://doi.org/10.1007/s11829-015-9358-z

Pitrat M. Vegetables I. Melon. In: Prohens J, Nuez F, editors. Vegetables I: Asteraceae, Brassicaceae, Chenopodiaceae, and Cucurbitaceae. New York (NY): Springer; 2008. p. 283-315. https://doi.org/10.1007/s1367-30443-4_9

Pitrat M. Phenotypic diversity in wild and cultivated melons (*Cucumis melo*). Plant Biotechnol. 2013;30(3):273-278. https://doi.org/10.5511/plantbiotechnology.13.0813a

R Core Team. R: a language and environment for statistical computing. Vienna (Austria): R Foundation for Statistical Computing; 2020. https://www.R-project.org/

Rader R, Howlett BG, Cunningham SA, Westcott DA, Newstrom-Lloyd LE, Walker MK, Teulon DAJ, Edwards W. Alternative pollinator taxa are equally efficient but not as effective as the honeybee in a mass flowering crop. J Appl Ecol. 2009;46(5):1080-1087. https://doi.org/10.1111/j.1365-2664.2009.01700.x

Revanasidda A, Belavadi V. Floral biology and pollination in *Cucumis melo* L., a tropical andromonoecious cucurbit. J Asia-Pac Entomol. 2019;22(1):215-225. https://doi.org/10.1016/j.aspen.2019.01.001

Robinson WS, Fell RD. Effect of honey bee foraging behaviors on "Delicious" apple set. HortScience. 1981;16(3):326-328. https://doi.org/10.21273/hortsci.16.3.326

Rodrigo Gomez S, Ornosa C, Garcia Gila J, Blasco-Aróstegui J, Selfa J, Guara M, Polidori C. Bees and crops in Spain: an update for melon, watermelon and almond. Ann Soc Entomol Fr (N.S.). 2021;57(1):12-28. https://doi.org/10.1080/00379271.2020.1847191

Rollin O, Garibaldi LA. Impacts of honeybee density on crop yield: a meta-analysis. J Appl Ecol. 2019;56(5):1152-1163. https://doi.org/10.1111/1365-2664.13355

Roquer-Beni L, Rodrigo A, Arnan X, Klein AM, Fornoff F, Boreux V, Bosch J. A novel method to measure hairiness in bees and other insect pollinators. Ecol Evol. 2020;10(6):2979-2990. https://doi.org/10.1002/ece3.6112

Rotjan RD, Calderone NW, Seeley TD. How a honey bee colony mustered additional labor for the task of pollen foraging. Apidologie. 2002;33(4):367-373. https://doi.org/10.1051/apido:2002026

Russo L, de Keyzer CW, Harmon-Threatt AN, LeCroy KA, MacIvor JS. The managed-to-invasive species continuum in social and solitary bees and impacts on native bee conservation. Curr Opin Insect Sci. 2021;46:43-49. https://doi.org/10.1016/j.cois.2021.01.001

Sagili RR, Breece CR, Simmons R, Borden JH. Potential of honeybee brood pheromone to enhance foraging and yield in hybrid carrot seed. HortTechnology. 2015;25(1):98-104. https://doi.org/10.21273/horttech.25.1.98

Sapir G, Baras Z, Azmon G, Goldway M, Shafir S, Allouche A, Stern E, Stern RA. Synergistic effects between bumblebees and honey bees in apple orchards increase cross pollination, seed number and fruit size. Sci Hortic. 2017;219:107-117. https://doi.org/10.1016/j.scienta.2017.03.010
Kalev H, Dag A, Shafir S. Feeding pollen supplements to honey bee colonies during pollination of sweet pepper in enclosures. Am Bee J. 2002;142(9):675-679.

Kitaoka TK, Nieh JC. Bumble bee pollen foraging regulation: role of pollen quality, storage levels, and odor. Behav Ecol Sociobiol. 2009;63(4):625-625. https://doi.org/10.1007/s00265-008-0707-0

Klein AM, Vaissiere BE, Cane JH, Steffan-Dewenter I, Cunningham SA, Kremen C, Tscharntke T. Importance of pollinators in changing landscapes for world crops. Proc Biol Sci. 2007;274(1608):303-313. https://doi.org/10.1098/rspb.2006.3721

Koski MH, Ison JL, Padilla A, Pham AQ, Galloway LF. Linking pollinator efficiency to patterns of pollen limitation: small bees exploit the plant-pollinator mutualism. Proc Biol Sci. 2018;285(1880):20180635. https://doi.org/10.1098/rspb.2018.0635

Kouonon LC, Jacquemart AL, Zoro Bi AI, Bertin P, Baudoin JP, Dje Y. Reproductive biology of the andromonoecious *Cucumis melo* subsp. *agrestis* (Cucurbitaceae). Ann Bot (Lond). 2009;104(6):1129-1139. https://doi.org/10.1093/aob/mcp196

Kuznetsova A, Brockhoff PB, Christensen RHB. ImerTest package: tests in linear mixed effects models. J Stat Softw. 2017:82(13):1-26. https://doi.org/10.18637/jss.v082.i13

Lamontagne-Drolet M, Samson-Robert O, Giovenazzo P, Fournier V. The impacts of two protein supplements on commercial honey bee (Apis mellifera L.) colonies. J Apic Res. 2019;58(5):800-813. https://doi.org/10.1080/00218839.2019.1644938

Maia-Silva C, Hrncir M, Imperatriz-Fonseca VL, Schorkopf DLP. Stingless bees (*Melipona subnita*ida) adjust brood production rather than foraging activity in response to changes in pollen stores. J Comp Physiol A. 2016;202(9-10):723-732. https://doi.org/10.1007/s00359-016-1095-y

Mann LK. Honey bee activity in relation to pollination and fruit set in the cantaloupe (*Cucumis melo*). Am J Bot. 1953;40(7):545-553. https://doi.org/10.1002/j.1537-2197.1953.tb06518.x

Mann LK, Robinson J. Fertilization, seed development, and fruit growth as related to fruit set in the cantaloupe (*Cucumis melo* L.). Am J Bot. 1950;37(9):685-697. https://doi.org/10.1002/j.1537-2197.1950.tb11058.x

Mayer DF. Sequential introduction of honey bee colonies for pear pollination. Acta Hortic. 1994:367(367):267-269. https://doi.org/10.17660/actahortic.1994.367.35

McGregor SE, Levin MD, Foster RE. Honey bee visitors and fruit set of cantaloups. J Econ Entomol. 1965;58(5):968-970. https://doi.org/10.1093/jee/58.5.968

McGregor SE, Todd FE. Cantaloup production with honey bees. J Econ Entomol. 1952;45(1):43-47. https://doi.org/10.1093/jee/45.1.43

Morales CL, Sáez A, Garibaldi LA, Aizen MA. Disruption of pollination services by invasive pollinator species. In: Vilà M, and Hulme PE, editors. Impact of Biological Invasions on Ecosystem Services. Cham (Switzerland): Springer; 2017.p. 203-220.

Muff S, Nilsen EB, O'Hara RB, Nater CR. Rewriting results sections in the language of evidence. Trends Ecol Evol. 2022;37(3):203-210. https://doi.org/10.1016/j.tree.2021.10.009

Noordyke ER, Ellis JD. Reviewing the efficacy of pollen substitutes as a management tool for improving the health and productivity of western honey bee (*Apis mellifera*) colonies. Front Sustain Food Syst. 2021;5:772897. https://doi.org/10.3389/fsufs.2021.772897

Noordyke ER, Santen E. van Ellis JD. Tracing the fate of pollen substitute patties in Western honey bee (Hymenoptera: Apidae) colonies. J Econ Entomol. 2021;114(4):1421-1430. https://doi.org/10.1093/jee/toab083

Norden BMB. The comparative importance of small carpenter bees (*Ceratina spp.*) and other insects to pollination of muskmelon/cantaloupe (*Cucumis melo* L.) in Maryland [Dissertation]. [College Park (MD)]: University of Maryland; 1985.

Orr N, Eisikowitch D. Interaction between melon (*Cucumis melo*) flowers and honeybees under extreme desert conditions in Israel. Apidologie. 1988;19(1):85-96. https://doi.org/10.1051/apido:19880106

Osterman J, Theodorou P, Radzevičiūtė R, Schnitker P, Paxton RJ. Apple pollination is ensured by wild bees when honey bees are drawn away from orchards by a mass co-flowering crop, oilseed rape. Agric Ecosyst Environ. 2021;315:107383. http://doi.org/10.1016/j.agee.2021.107383

Page ML, Nicholson CC, Brennan RM, Britzman AT, Greer J, Hemberger J, Kahl H, Müller U, Peng Y, Rosenberger NM, et al. A meta-analysis of single visit pollination effectiveness comparing honeybees and other floral visitors. Am J Bot. 2021;108(11):2196-2207. https://doi.org/10.1002/ajb2.1764

Page Jr RE, Waddington KD, Hunt GJ, Fondrk MK. Genetic determinants of honey bee foraging behaviour. Anim Behav. 1995;50(6):1617-1625. https://doi.org/10.1016/0003-3472(95)80015-8

Pankiw T. Brood pheromone regulates foraging activity of honey bees (Hymenoptera: Apidae). J Econ Entomol. 2004;97(3):748-751. https://doi.org/10.1093/jee/97.3.748

Pankiw T, Page RE Jr, Fondrk MK. Brood pheromone stimulates pollen foraging in honey bees (*Apis mellifera*). Behav Ecol Sociobiol. 1998;44:193-198. https://doi.org/10.1007/s002650050531

Park MG, Raguso RA, Losey JE, Danforth BN. Per-visit pollinator performance and regional importance of wild *Bombus* and *Andrena* (*Melandrena*) compared to the managed honey bee in New York apple orchards. Apidologie. 2016;47(2):145-160. https://doi.org/10.1007/s13592-015-0383-9

Parker AJ, Tran JL, Ison JL, Bai JDK, Weis AE, Thomson JD. Pollen packing affects the function of pollen on corbiculate bees but not non-corbiculate bees. Arthropod Plant Interact. 2015;9(2):197-203. https://doi.org/10.1007/s11829-015-9358-z

Pitrat M. Vegetables I. Melon. In: Prohens J, Nuez F, editors. Vegetables I: Asteraceae, Brassicaceae, Chenopodiaceae, and Cucurbitaceae. New York (NY): Springer; 2008. p. 283-315. https://doi.org/10.1007/s11829-015-9358-z

Pitrat M. Phenotypic diversity in wild and cultivated melons (*Cucumis melo*). Plant Biotechnol. 2013;30(3):273-278. https://doi.org/10.5511/plantbiotechnology.13.0813a

R Core Team. R: a language and environment for statistical computing. Vienna (Austria): R Foundation for Statistical Computing; 2020. https://www.R-project.org/

Rader R, Howlett BG, Cunningham SA, Westcott DA, Newstrom-Lloyd LE, Walker MK, Teulon DAJ, Edwards W. Alternative pollinator taxa are equally efficient but not as effective as the honeybee in a mass flowering crop. J Appl Ecol. 2009;46(5):1080-1087. https://doi.org/10.1111/j.1365-2664.2009.01700.x

Revanasidda A, Belavadi V. Floral biology and pollination in *Cucumis melo* L., a tropical andromonoecious cucurbit. J Asia-Pac Entomol. 2019;22(1):215-225. https://doi.org/10.1016/j.aspen.2019.01.001

Robinson WS, Fell RD. Effect of honey bee foraging behaviors on "Delicious" apple set. HortScience. 1981;16(3):326-328. https://doi.org/10.21273/hortsci.16.3.326

Rodrigo Gomez S, Ornosa C, Garcia Gila J, Blasco-Aróstegui J, Selfa J, Guara M, Polidori C. Bees and crops in Spain: an update for melon, watermelon and almond. Ann Soc Entomol Fr (N.S.). 2021;57(1):12-28. https://doi.org/10.1080/00379271.2020.1847191

Rollin O, Garibaldi LA. Impacts of honeybee density on crop yield: a meta-analysis. J Appl Ecol. 2019;56(5):1152-1163. https://doi.org/10.1111/1365-2664.13355

Roquer-Beni L, Rodrigo A, Arnan X, Klein AM, Fornoff F, Boreux V, Bosch J. A novel method to measure hairiness in bees and other insect pollinators. Ecol Evol. 2020;10(6):2979-2990. https://doi.org/10.1002/ece3.6112

Rotjan RD, Calderone NW, Seeley TD. How a honey bee colony mustered additional labor for the task of pollen foraging. Apidologie. 2002;33(4):367-373. https://doi.org/10.1051/apido:2002026

Russo L, de Keyzer CW, Harmon-Threatt AN, LeCroy KA, MacIvor JS. The managed-to-invasive species continuum in social and solitary bees and impacts on native bee conservation. Curr Opin Insect Sci. 2021;46:43-49. https://doi.org/10.1016/j.cois.2021.01.001

Sagili RR, Breece CR, Simmons R, Borden JH. Potential of honeybee brood pheromone to enhance foraging and yield in hybrid carrot seed. HortTechnology. 2015;25(1):98-104. https://doi.org/10.21273/horttech.25.1.98

Sapir G, Baras Z, Azmon G, Goldway M, Shafir S, Allouche A, Stern E, Stern RA. Synergistic effects between bumblebees and honey bees in apple orchards increase cross pollination, seed number and fruit size. Sci Hortic. 2017;219:107-117. https://doi.org/10.1016/j.scienta.2017.03.010
Schmickl T, Crailsheim K. Inner nest homeostasis in a changing environment with special emphasis on honey bee brood nursing and pollen supply. *Apidologie*. 2004;35(3):249–263. https://doi.org/10.1051/apido:2004019

Schneider CA, Rasband WS, Eliceiri KW. NIH Image to ImageJ: 25 years of image analysis. Nat Methods. 2012;9(7):671–675. https://doi.org/10.1038/nmeth.2089

Seeley TD. The foraging abilities of a colony. In: TD. Seeley, editor. The Wisdom of the Hive: the Social Physiology of Honey Bee Colonies. Cambridge (MA): Harvard University Press; 1995. p. 46–68.

Shafir S. Bee cognition and crop pollination: proven and potential applications. In: Seckbach J, Dubinsky Z, editors. All Flesh Is Grass: Plant-Animal Interrelationships. Dordrecht (Netherlands): Springer; 2011. p. 183–198. https://doi.org/10.1007/978-90-481-9316-5_8

Stavert JR, Liñán-Cembrano G, Beggs JR, Howlett BG, Pattemore DE, Bartomeus I. Hairiness: the missing link between pollinators and pollination. PeerJ. 2016;4:e2779. https://doi.org/10.7717/peerj.2779

Stern R, Eisikowitch D, Dag A. Sequential introduction of honeybee colonies and doubling their density increases cross-pollination, fruit-set and yield in “Red Delicious” apple. J Hortic Sci Biotechnol. 2001;76(1):17–23. https://doi.org/10.1080/14620316.2001.11511320

Stern RA, Goldway M, Zisovich AH, Shafir S, Dag A. Sequential introduction of honeybee colonies increases cross-pollination, fruit-set and yield of “Spadona” pear (*Pyrus communis* L.). J Hortic Sci Biotechnol. 2004;79(4):652–658. https://doi.org/10.1080/14620316.2004.11511821

Stern RA, Zisovich AH, Shafir S, Dag A, Goldway M. Increasing the yield of “spadona” pear (*Pyrus communis* L.) by appropriate utilization of beehives. Acta Hortic. 2005;671(671):143–150. https://doi.org/10.17660/actahortic.2005.671.17

Thomson JD, Goodell K. Pollen removal and deposition by honeybee and bumblebee visitors to apple and almond flowers. J Appl Ecol. 2001;38(5):1032–1044. https://doi.org/10.1046/j.1365-2664.2001.00657.x

Tschoeke PH, Oliveira EE, Dalcin MS, Silveira-Tschoeke MCA, Santos GR. Diversity and flower-visiting rates of bee species as potential pollinators of melon (*Cucumis melo* L.) in the Brazilian Cerrado. Sci Horticult. 2015;186:207–216. https://doi.org/10.1016/j.scienta.2015.02.027

Tsirakoglou V, Thrasyvoulou A, Hatjina F. Techniques to increase the attractiveness of kiwi flowers to honey bees. Acta Hortic. 1997;444(444):439–452. https://doi.org/10.17660/actahortic.1997.444.68

Vaissière BE. Measure of pollination intensity and associated parameters. In: Honey bees, *Apis mellifera* L. (Hymenoptera: Apidae), as pollinators of upland cotton, *Gossypium hirsutum* L. (Malvaceae), for hybrid seed

production. Dissertation. College Station (TX): Texas A&M University; 1991. p. 22–95.

Vaissière, BE, Freitas BM, Gemill-Herren B. Protocol to detect and assess pollination deficits in crops: a handbook for its use. Rome (Italy): FAO; 2011.

Vaissière BE, Froissart R. Pollination of cantaloupe under spun bonded row cover by honey bees (Hymenoptera: Apidae) in West Africa. J Econ Entomol. 1996;89(5):1213–1222. https://doi.org/10.1093/jee/89.5.1213

Vaissière BE, Malaboeuf F, Rodet G. Viability of cantaloupe pollen carried by honeybees *Apis mellifera* varies with foraging behavior. Naturwissenschaften. 1996;83(2):84–86. https://doi.org/10.1007/BF01141876

Valentin M, Gary C, Vaissiere BE, Frossard JS. Effect of fruit load on partitioning of dry matter and energy in cantaloupe (*Cucumis melo* L.). Ann Bot (Lond). 1999;84(2):173–181. https://doi.org/10.1006/anbo.1999.0904

Valentin-Morison M, Vaissiere BE, Gary C, Robin P. Source-sink balance affects reproductive development and fruit quality in cantaloupe melon (*Cucumis melo* L.). J Hortic Sci Biotechnol. 2006;81(1):105–117. https://doi.org/10.1080/14620316.2006.11512036

Vaughan DM, Calderone NW. Assessment of pollen stores by foragers in colonies of the honey bee, *Apis mellifera* L. Insectes Soc. 2002;49(1):23–27. https://doi.org/10.1007/s00040-002-8273-3

Venables WN, Ripley BD. Modern applied statistics with S. 4th ed. New York (NY): Springer; 2002.

Webster TC, Thorp RW, Briggs D, Skinner J, Parisian T. Effects of pollen traps on honey bee (Hymenoptera: Apidae) foraging and brood rearing during almond and prune pollination. Environ Entomol. 1985;14(6):683–686. https://doi.org/10.1093/ee/14.6.683

Weidenmüller A, Tautz J. In-hive behavior of pollen foragers (*Apis mellifera*) in honey bee colonies under conditions of high and low pollen need. Ethology. 2002;108(3):205–221. https://doi.org/10.1046/j.1439-0310.2002.00759.x

Weinman LR, Ress T, Gardner J, Winfree R. Individual bee foragers are less efficient transporters of pollen for the plants from which they collect the most pollen into their scopae. Am J Bot. 2023;110(6):e16178. https://doi.org/10.1002/ajb2.16178

Young HJ, Dunning DW, von Hasseln KW. Foraging behavior affects pollen removal and deposition in *Impatiens capensis* (Balsaminaceae). Am J Bot. 2007;94(7):1267–1271. https://doi.org/10.3732/ajb.94.7.1267

Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM. Mixed effects models and extensions in ecology with R. New York (NY): Springer; 2009. https://doi.org/10.1007/978-0-387-87458-6
Schmickl T, Crailsheim K. Inner nest homeostasis in a changing environment with special emphasis on honey bee brood nursing and pollen supply. *Apidologie*. 2004;35(3):249–263. https://doi.org/10.1051/apido:2004019

Schneider CA, Rasband WS, Eliceiri KW. NIH Image to ImageJ: 25 years of image analysis. Nat Methods. 2012;9(7):671–675. https://doi.org/10.1038/nmeth.2089

Seeley TD. The foraging abilities of a colony. In: TD. Seeley, editor. The Wisdom of the Hive: the Social Physiology of Honey Bee Colonies. Cambridge (MA): Harvard University Press; 1995. p. 46–68.

Shafir S. Bee cognition and crop pollination: proven and potential applications. In: Seckbach J, Dubinsky Z, editors. All Flesh Is Grass: Plant-Animal Interrelationships. Dordrecht (Netherlands): Springer; 2011. p. 183–198. https://doi.org/10.1007/978-90-481-9316-5_8

Stavert JR, Liñán-Cembrano G, Beggs JR, Howlett BG, Pattemore DE, Bartomeus I. Hairiness: the missing link between pollinators and pollination. PeerJ. 2016;4:e2779. https://doi.org/10.7717/peerj.2779

Stern R, Eisikowitch D, Dag A. Sequential introduction of honeybee colonies and doubling their density increases cross-pollination, fruit-set and yield in “Red Delicious” apple. J Hortic Sci Biotechnol. 2001;76(1):17–23. https://doi.org/10.1080/14620316.2001.11511320

Stern RA, Goldway M, Zisovich AH, Shafir S, Dag A. Sequential introduction of honeybee colonies increases cross-pollination, fruit-set and yield of “Spadona” pear (*Pyrus communis* L.). J Hortic Sci Biotechnol. 2004;79(4):652–658. https://doi.org/10.1080/14620316.2004.11511821

Stern RA, Zisovich AH, Shafir S, Dag A, Goldway M. Increasing the yield of “spadona” pear (*Pyrus communis* L.) by appropriate utilization of beehives. Acta Hortic. 2005;671(671):143–150. https://doi.org/10.17660/actahortic.2005.671.17

Thomson JD, Goodell K. Pollen removal and deposition by honeybee and bumblebee visitors to apple and almond flowers. J Appl Ecol. 2001;38(5):1032–1044. https://doi.org/10.1046/j.1365-2664.2001.00657.x

Tschoeke PH, Oliveira EE, Dalcin MS, Silveira-Tschoeke MCA, Santos GR. Diversity and flower-visiting rates of bee species as potential pollinators of melon (*Cucumis melo* L.) in the Brazilian Cerrado. Sci Horticult. 2015;186:207–216. https://doi.org/10.1016/j.scienta.2015.02.027

Tsirakoglou V, Thrasyvoulou A, Hatjina F. Techniques to increase the attractiveness of kiwi flowers to honey bees. Acta Hortic. 1997;444(444):439–452. https://doi.org/10.17660/actahortic.1997.444.68

Vaissière BE. Measure of pollination intensity and associated parameters. In: Honey bees, *Apis mellifera* L. (Hymenoptera: Apidae), as pollinators of upland cotton, *Gossypium hirsutum* L. (Malvaceae), for hybrid seed

production. Dissertation. College Station (TX): Texas A&M University; 1991. p. 22–95.

Vaissière, BE, Freitas BM, Gemill-Herren B. Protocol to detect and assess pollination deficits in crops: a handbook for its use. Rome (Italy): FAO; 2011.

Vaissière BE, Froissart R. Pollination of cantaloupes under spun bonded row cover by honey bees (Hymenoptera: Apidae) in West Africa. J Econ Entomol. 1996;89(5):1213–1222. https://doi.org/10.1093/jee/89.5.1213

Vaissière BE, Malaboeuf F, Rodet G. Viability of cantaloupe pollen carried by honeybees *Apis mellifera* varies with foraging behavior. *Naturwissenschaften*. 1996;83(2):84–86. https://doi.org/10.1007/BF01141876

Valentin M, Gary C, Vaissiere BE, Frossard JS. Effect of fruit load on partitioning of dry matter and energy in cantaloupe (*Cucumis melo* L). Ann Bot (Lond). 1999;84(2):173–181. https://doi.org/10.1006/anbo.1999.0904

Valentin-Morison M, Vaissiere BE, Gary C, Robin P. Source-sink balance affects reproductive development and fruit quality in cantaloupe melon (*Cucumis melo* L.). J Hortic Sci Biotechnol. 2006;81(1):105–117. https://doi.org/10.1080/14620316.2006.11512036

Vaughan DM, Calderone NW. Assessment of pollen stores by foragers in colonies of the honey bee, *Apis mellifera* L. Insectes Soc. 2002;49(1):23–27. https://doi.org/10.1007/s00040-002-8273-3

Venables WN, Ripley BD. Modern applied statistics with S. 4th ed. New York (NY): Springer; 2002.

Webster TC, Thorp RW, Briggs D, Skinner J, Parisian T. Effects of pollen traps on honey bee (Hymenoptera: Apidae) foraging and brood rearing during almond and prune pollination. Environ Entomol. 1985;14(6):683–686. https://doi.org/10.1093/ee/14.6.683

Weidenmüller A, Tautz J. In-hive behavior of pollen foragers (*Apis mellifera*) in honey bee colonies under conditions of high and low pollen need. Ethology. 2002;108(3):205–221. https://doi.org/10.1046/j.1439-0310.2002.00759.x

Weinman LR, Ress T, Gardner J, Winfree R. Individual bee foragers are less efficient transporters of pollen for the plants from which they collect the most pollen into their scopae. Am J Bot. 2023;110(6):e16178. https://doi.org/10.1002/ajb2.16178

Young HJ, Dunning DW, von Hasseln KW. Foraging behavior affects pollen removal and deposition in *Impatiens capensis* (Balsaminaceae). Am J Bot. 2007;94(7):1267–1271. https://doi.org/10.3732/ajb.94.7.1267

Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM. Mixed effects models and extensions in ecology with R. New York (NY): Springer; 2009. https://doi.org/10.1007/978-0-387-87458-6