DOI: 10.5061/dryad.9s4mw6mm9
title: Data from: Commercial Bombus impatiens colonies function as ecological traps for wild queens

description: 1. In response to anthropogenic environmental change, the cues that
 animals use throughout their lifecycle to optimize fitness may become
 unreliable, resulting in an ecological trap. 2. Here we investigated
 whether commercial bumble bee (Bombus impatiens) colonies managed for
 early spring crop pollination act as ecological traps for wild
 nest-searching Bombus queens by subverting their natural nest usurpation
 behavior. 3. An average of 10 dead wild queens were recovered from each
 standard colony during the two-week period of the experiment, but colonies
 with queen excluders were successful in preventing wild queen deaths. The
 use of queen excluders did not impact colony performance in terms of
 resident queen survival, colony reproduction, colony weight gain or worker
 body size. 4. Sites where wild nest-searching queens were small had higher
 rates of failed usurpation, suggesting smaller-sized queens are
 disproportionately at risk from failed usurpation. Furthermore, sites
 where commercial colonies without queen excluders were introduced for
 spring crop pollination had fewer bumble bee visits to a later-blooming
 crop compared to sites without commercial colonies. 5. Synthesis and
 applications. Our findings reveal a novel mechanism by which commercial
 colonies can negatively impact wild bumble bee populations and their
 pollination services. At the same time, we demonstrate a simple and
 inexpensive risk mitigation tool – a queen excluder – was 100% effective
 at eliminating this risk without compromising colony performance.
 Commercial colonies used outdoors during the bumble bee nest-searching
 period should be fit with queen excluders to prevent negative impacts on
 wild pollinator communities and their services.
description: Do commercial colonies function
 as an ecological trap and can queen excluders prevent this
 effect? To
 investigate whether wild bumble bee (Bombus spp.) queens enter and are
 killed by commercial bumble bee colonies, we placed two commercial Bombus
 impatiens colonies (BioBest; Romulus, Michigan, USA) at eight apple
 orchards in the Finger Lakes region of New York state on May 13th, 2020,
 shortly before apple bloom. Permission from farm managers was granted for
 all research and collections from privately owned land and ethical
 approval for the use and collection of the bumble bees was not required.
 All orchards except one were conventionally managed and orchards ranged in
 size from 2 to more than 30 acres. Each colony contained ~75 workers,
 worker brood, and a laying queen, and was fitted with two flight openings
 that could be set to be open or closed with a rotating slide. We confirmed
 that each colony contained only one queen and no queen cells and marked
 the resident queen with a paint mark. In all colonies from this supplier,
 one opening allowed bumble bees to enter and exit the colony freely,
 whereas a second opening allowed bumble bees to enter the colony but
 generally not exit. At every site, one of the two colonies was fitted with
 a queen excluder over the enter/exit flight opening, reducing the opening
 from 16 mm to 5 mm and allowing workers but not queens to pass both in and
 out of the colony (Fig. 1).  The second colony at each site was maintained
 in the standard configuration and did not use a queen excluder therefore
 serving as a control colony. Because the supplier only provides queen
 excluders on the enter/exit flight opening, the enter-only flight opening
 of the queen excluder colony remained closed at all times to prevent wild
 queens from entering the colony. In contrast, for standard control
 colonies, both flight openings were set to open. Colonies were placed on
 orchard edges within weather-resistant quad boxes (Fig. 1b) for the
 duration of apple bloom and were recovered on May 26th. To compare numbers
 of dead queens that accumulated in excluder versus standard colonies deployed at the same site over
 the same time period, at the end of the experiment colonies were
 anesthetized with CO2 for 1-2 minutes and all dead queens and non-B.
 impatiens arthropods were removed and counted.
 Do queen excluders impact colony
 performance or demographics? We studied the effects of a queen excluder on
 colony performance and demographics to determine whether there were
 impacts of using queen excluders in terms of colony productivity,
 investment in workers or on resident queen survival. Within 24 hours after
 colonies were recovered, final colony weight measurements were recorded
 and compared to initial colony weight measures taken in the 24-hour period
 before colonies were deployed. We recorded whether resident colony queens
 were dead or alive to assess whether queen excluders influence resident
 queen survival. Additionally, we assessed colony reproduction by counting
 the number of queen cells and taking pictures of the colony to later count
 the number of workers. To determine whether a queen excluder influenced
 the body size of the workers that would defend against colony invaders,
 each colony was agitated and 15 workers that came out to attack the
 agitators were captured. We measured the body size of the attacking
 workers by recording their intertegular distance (ITD) using Zen software
 connected to a Zeiss Stemi 305 microscope (Carl Zeiss Microscopy,
 LLC).           
   Do queen
 body size and wild queen abundance influence the number of dead queens that accumulate
 in a colony? To determine whether queens that entered and died
 in a colony differed in size from the average wild queens at a site, we
 haphazardly collected five wild B. impatiens queens that were foraging or
 nest searching at the eight sites between May 29th and June 1st. We also
 looked at whether dead queens differed in body size from resident colony
 queens that had retained their paint mark by the end of the experiment. We
 measured the inter-tegular distance (ITD) of the dead wild, live wild and
 resident colony queens using the same software and microscope described
 above. Though dead wild queens had dried somewhat, the majority were still
 pliable and prior studies have found little difference in ITD between
 fresh and dried Bombus specimens (Hagen & Dupont, 2013). Therefore, we do not expect size differences as
 measured by ITD to be impacted by differences in sample moisture
 content.  Additionally, we evaluated whether local B.
 impatiens queen abundance affected the number of queens that invaded a
 colony and died. We visited each site three times during apple bloom to
 measure local queen density by slowly walking at a consistent pace 25 m
 transects along the orchard edge and counting nest-searching, foraging,
 and flying B. impatiens queens that were identified visually within 5
 meters in both directions. During the first round of site visits, two
 transects were walked at each site. Due to low counts observed across all
 sites during the first round, this was increased to six transects during
 subsequent rounds. Does presence of commercial colonies during
 nest-founding impact bumble bee visitation to a later-blooming
 crop? To
 evaluate the impact of commercial B. impatiens colonies on crop visitation
 under realistic conditions, we explored visitation patterns from a large
 field study that had been conducted in the prior two years which used
 colonies without queen excluders from Koppert Biological Systems (Howell,
 Michigan, USA) in strawberry fields during bloom on eight farms in May
 2018 and five farms in May 2019. For this study we selected farms that
 grew both strawberry, an early blooming crop, as well as tomato, which
 blooms later in the season and is visited predominantly by bumble bees
 (Toni, Djossa, Ayenan,
 & Teka, 2020). Each
 farm that received colonies was paired with a nearby farm that also grew
 strawberries and tomatoes but did not receive commercial bumble bee
 colonies. In total 16 farms were surveyed in 2018 and 10 farms were
 surveyed in 2019. Strawberry fields were stocked at the recommended
 density of two colonies per acre of strawberries resulting in a range of
 1-16 colonies per farm.  Colonies were arranged in quads and distributed
 within or at the edge of the field.
             Because this
 experiment was designed to measure the impact of commercial bumble bee
 colonies on visitation to both crops, colonies were relocated following
 strawberry bloom a short distance to tomato field edges on farms that
 received commercial colonies. We began visitation surveys on tomatoes in
 early June during 2018 and late June in 2019. On both farms with and
 without commercial colonies, we recorded visits to tomato flowers by B.
 impatiens as well as those from wild bees including other bumble bee
 species during a 30-minute period while walking through the tomato field.
 A visit and visitor identity were recorded when a bee contacted a tomato
 flower. Surveyors counted all visits within their visual field while
 walking at a consistent pace along a row and attempted not to sample the
 same area in an individual survey bout. Tomato fields were surveyed three
 times in 2018 and four times in 2019 from early June to early
 July. Other Bombus species
 were combined with other wild bee species for analysis as only 0.5% of
 visits were attributed to these other Bombus species, and failed
 usurpation attempts were largely constrained to B.
 impatiens.