DOI: 10.5061/dryad.s7h44j154
title: Honey bee lifespan: the critical role of pre-foraging stage

description: Assessing the various anthropogenic pressures imposed on honey bees
 requires characterizing the patterns and drivers of natural mortality.
 Using automated life-long individual monitoring devices, we monitored
 worker bees in different geographical, seasonal and colony contexts
 creating a broad range of hive conditions. We measured their life-history
 traits and notably assessed whether lifespan is influenced by pre-foraging
 flight experience. Our results show that the age at the first flight and
 onset of foraging are critical factors that determine, to a large extent,
 lifespan. Most importantly, our results indicate that a large proportion
 (40%) of the bees die during pre-foraging stage, and for those surviving,
 the elapsed time and flight experience between the first flight and the
 onset of foraging is of paramount importance to maximize the number of
 days spent foraging. Once in the foraging stage, individuals experience a
 constant mortality risk of 9% and 36% per hour of foraging and per
 foraging day, respectively. In conclusion, the pre-foraging stage during
 which bees perform orientation flights is a critical driver of bee
 lifespan. We believe these data on the natural mortality risks in honey
 bee workers will help assess the impact of anthropogenic pressures on
 bees.
description: To date, two main
 techniques are available to monitor the in-and-out activity of honey bees
 at the beehive entrance, the Radio-Frequency Identification device (RFID)
 (49) and the optical counter based on image identification of barcode tags
 (50, 51). With such devices, the time-activity budgets of flights
 (duration and number of trips per day) are similarly recorded at the
 individual level. We equipped three colonies with RFID in 2011 in the Long
 Term Social-Ecological Research “Zone Atelier Plaine & Val de
 Sèvre” (LTSER ZA-PVS) (52) in central western France (46°23’N-0°41’W, site
 A, Figure 1), and one colony with image-based optical counters in 2018 at
 the National Institute for Agriculture, Food and Environment of Avignon in
 southeastern France (43°54’N-4°-52’E, site B, Figure 1). The RFID device
 consists of two adjacent rows of five contiguous RFID readers (iID2000,
 2k6 HEAD; Microsensys GmbH, Erfurt, Germany) placed at the entrance of the
 hives (Figure 1). The image-based optical counter comprises a camera that
 monitors the hive entrance and image analysis software that detects and
 registers the barcode (50, 51). These two geographical areas vary in
 climate context (Oceanic for site A and Mediterranean for site B), giving
 different colony dynamics (e.g. different timing of peak brood
 production). Beyond this inter-regional
 variability, we further introduced intra-regional variations in bee
 life-history traits (Figure 1). To do so, cohorts of bees were tagged each
 month from April to September in both sites to add seasonal variation. In
 addition, we simulated a third factor of variation by manipulating the
 environment of tagged bees (Figure 1). In site A, all tagged bees came
 from a single source colony (<i>A. mellifera mellifera</i> ×
 <i>caucasica</i> strain) but were introduced into three
 monitored beehives (common 10-frame Dadant-Blatt model with sister queen
 of <i>A. mellifera mellifera</i> ×
 <i>caucasica</i> strain) placed  about 30 km from the source
 location. Moreover, the three monitored colonies were separated from each
 other by about 15km to provide independent foraging landscapes of the
 tagged bees. In site B, tagged bees that were introduced each month in a
 single monitored colony came from three source colonies
 (<i>A.</i> <i>mellifera</i>
 <i>mellifera</i> × <i>ligustica</i> strain for the
 source and monitored colonies). Hence bees could be identified based on
 their colony of origin. These two different scenarios allowed the creation
 of variability in environmental and colony contexts with potential effects
 on bee life history. To monitor individuals throughout
 their entire adult life, we collected newly emerged bees. Bees were
 selected from brood frames containing late-stage pupae, all adult bees
 were removed from this frame and placed in an incubator at 34°C and 50–70%
 humidity. Newly emerged bees were then collected after 2-10 hours of
 incubation and tagged. In site A, tags consisted of RFID microchips of 1.0
 mm × 1.6 mm × 0.5 mm (mic3® - TAG 64 bit RO, iID2000, 13.56 MHz system,
 Microsensys GmbH, Erfurt, Germany). RFID tags weighed approx. 3 mg, i.e. 3
 % of an adult honey bee’s body mass. This weight is considered low enough
 to not interfere with the individual life and tasks (49). In site B, tags
 consisted of data-matrix barcodes (3mm diameter) printed on laminated
 paper. Both tag types were glued on the bee thorax using biocompatible
 dental cement (TempoSIL2®) in site A and Sader® glue in site B. Because
 bee weight might influence flying capabilities (46), in site B, all newly
 emerged bees were weighed individually before tagging in order to assess
 the potential influence of body weight at emergence on bee lifespan.
 Indeed, bee weight at emergence might vary according to their nutritional
 state during larval development (53).
 Tagged bees (less
 than 24h old) were then introduced into colonies equipped with monitoring
 systems and monitored until death in both sites. All colonies were
 adequately treated against the mite Varroa destructor each fall and no
 visible disease symptoms were observed.
description: Notes are provided in the R code.