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1. Sunflower pollen reduces a gut pathogen in worker and queen but not male bumble bees

   https://doi.org/10.1111/een.12915  

   Fowler, Alison E. ; Stone, Elyse C. ; Irwin, Rebecca E. ; Adler, Lynn S. ( July 2020 , Ecological Entomology)

   1. Social insect castes and sexes differ in many ways, including morphology, behavior, and sometimes ploidy level. Recent studies have found that consuming sunflower pollen reduces the gut pathogenCrithidia bombiin workers of the common eastern bumble bee (Bombus impatiens). Here, this work is extended to the reproductive individuals that represent colony fitness – males and queens – to assess if the medicinal effects of sunflower pollen vary with bee caste and sex.

   2. This study examined the effect of sunflower pollen compared to a diverse wildflower pollen mix on infection in worker, male, and daughter queen commercialB.impatiens. Bees were infected, fed either sunflower pollen or wildflower pollen for 7 days, and then infection levels were assessed.

   3. Compared to wildflower pollen, sunflower pollen dramatically reducedCrithidiainfection in workers and daughter queens, but not males. Infection levels were very low for both diets in males; this could be due to low pollen consumption or other mechanisms.

   4. ReducingCrithidiainfection in young queens before they undergo hibernation is important for population dynamics since infected queens are less likely to survive hibernation, and those that do are less likely to successfully establish a nest the following spring. Because sunflowers bloom in late summer when new queens are emerging, sunflowers could provide an important dietary component for queens during this critical life stage. Deepening our understanding of how diet impacts pathogens in reproductive bees, as well as workers, is crucial to maintain healthy pollinator populations.

    

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2. The costs and benefits of sunflower pollen diet on bumble bee colony disease and health

   https://doi.org/10.1002/ecs2.3663  

   Giacomini, Jonathan J. ; Connon, Sara J. ; Marulanda, Daniel ; Adler, Lynn S. ; Irwin, Rebecca E. ( July 2021 , Ecosphere)

   Pathogen transmission between domesticated and wild host species has important implications for community ecology, agriculture, and wildlife conservation. Bumble bees provide valuable pollination services that are vital for both wildflowers and agricultural production. Intense concerns about pathogen spillover from commercial bumble bees to wild bee populations, and the potential harmful effects of pathogen spillback to commercial bees, has stimulated a need for practical strategies that effectively manage bumble bee infectious diseases. Here, we assessed the costs and benefits of a medicinal sunflower pollen diet (Helianthusannuus) on whole‐colony bumble bee disease and performance using commercial colonies of the common eastern bumble bee,Bombus impatiens, and its protozoan pathogen,Crithidia bombi(Trypanosomatida). We first found that a 1:1 mixture of sunflower combined with wildflower pollen reducedC. bombiinfection prevalence and intensity within individualB. impatiensworkers by nearly 4‐fold and 12‐fold, respectively, relative to wildflower pollen. At the colony level, a 1:1 mixture of sunflower and wildflower pollen reducedC. bombiinfection prevalence by 11% averaged over a 10‐week period and infection intensity by 30% relative to wildflower pollen. Colony performance was similar between pollen diets and infection treatments, including the number of workers and immatures produced, and size and weight of workers, drones, and queens. Infection significantly reduced the probability of queen production in colonies fed a pure wildflower pollen diet, but not colonies fed a mixed sunflower pollen diet, suggesting that the medicinal benefits of a mixed sunflower pollen diet can reverse the negative effects of infection on reproductive success. This study provides evidence that sunflower pollen as part of a mixed pollen diet can reduce infection in individual bees and whole colonies with no significant nutritional trade‐offs for colony worker production and most aspects of colony reproduction. A supplemental mixed sunflower pollen diet may provide a simple and effective solution to reduce disease and improve the health of economically and ecologically important pollinators.

    

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3. Bumble Bee ( Bombus vosnesenskii ) Queen Nest Searching Occurs Independent of Ovary Developmental Status

   https://doi.org/10.1093/iob/obac007  

   Sarro, Erica ; Tripodi, Amber ; Woodard, S. Hollis ( February 2022 , Integrative Organismal Biology)

   Studies on the physiological states of wild-caught organisms are essential to uncovering the links between ecological and physiological processes. Bumble bee queens emerge from overwintering in the spring. At this time, queens develop their ovaries and search for a nest site in which to start a colony. Whether these two processes, ovary development and nest-searching, interact with or influence one another remains an unresolved question in behavioral physiology. We explored the hypothesis that ovary development and nest-searching might be mechanistically connected, by testing whether (1) ovary development precedes nest-searching behavior; (2) nest occupation precedes ovary development; or (3) ovary development and nest-searching occur independently, in bumble bee (Bombus vosnesenskii) queens. We collected queens either nest-searching (and thus prior to occupying a nest) or pollen-collecting (and thus provisioning an occupied nest) and measured their degree of ovary activation. We further screened these queens for parasites or other symbionts, to identify additional factors that may impact their reproductive success at this time. We found that queens searched for and occupied nests at all stages of ovary development, indicating that these processes occur independently in this system. Nest-searching queens were more likely to have substantial mite loads than pollen-collecting queens, who had already located and occupied a nest. However, mite loads did not significantly predict ovary developmental status. Collectively, our work shows that nesting status and symbionts alone are insufficient to explain the variation in spring bumble bee queen ovary development. We propose that ovary development and nest-searching occur opportunistically, which may enable queens to begin laying eggs earlier in the season than if these processes occurred in discrete succession.

    

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4. Contrasting effects of land cover on nesting habitat use and reproductive output for bumble bees

   https://doi.org/10.1002/ecs2.3642  

   Pugesek, Genevieve ; Crone, Elizabeth E. ( July 2021 , Ecosphere)

   Understanding habitat quality is central to understanding the distributions of species on the landscape, as well as to conserving and restoring at‐risk species. Although it is well known that many species require different resources throughout their life cycles, pollinator conservation efforts focus almost exclusively on forage resources. In this study, we evaluate nesting habitat for bumble bees by locating nests directly on the landscape. We compared colony density and colony reproductive output forBombus impatiens, the common eastern bumble bee, across three different land cover types (hay fields, meadows, and forests). We also assessed nesting habitat associations for allBombusnests located during surveys to tease apart species‐specific patterns of habitat use. We found thatB. impatiensnested under the ground in two natural land cover types, forests, and meadows, but found noB. impatiensnests in hay fields. ThoughB. impatiensnested at similar densities in both meadows and forests, colonies in forests had much higher reproductive output. In contrast,B. griseocollistended to nest on the surface of the ground and was almost always found in meadows.B. perplexiswas the only species to nest in all three habitat types, including hay fields. For some bumble bee species in this system, meadows, the habitat type with abundant forage resources, may be sufficient to maintain them throughout their life cycles. However,B. impatiensmight benefit from heterogeneous landscapes with forests and meadows. Results forB. impatiensemphasize the longstanding notion that habitat use is not always positively correlated with habitat quality (as measured by reproductive output). Our results also show that habitat selection by bumble bees at one spatial scale may be influenced by resources at other scales. Finally, we demonstrate the feasibility of direct nest searches for understanding bumble bee distribution and ecology.

    

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5. Developmental transcriptomes predict adult social behaviours in the socially flexible sweat bee, Lasioglossum baleicum

   https://doi.org/10.1111/mec.17244  

   Omufwoko, Kennedy S. ; Cronin, Adam L. ; Nguyen, Thi Thu Ha ; Webb, Andrew E. ; Traniello, Ian M. ; Kocher, Sarah D. ( December 2023 , Molecular Ecology)

   Natural variation can provide important insights into the genetic and environmental factors that shape social behaviour and its evolution. The sweat bee,Lasioglossum baleicum, is a socially flexible bee capable of producing both solitary and eusocial nests. We demonstrate that within a single nesting aggregation, soil temperatures are a strong predictor of the social structure of nests. Sites with warmer temperatures in the spring have a higher frequency of social nests than cooler sites, perhaps because warmer temperatures provide a longer reproductive window for those nests. To identify the molecular correlates of this behavioural variation, we generated a de novo genome assembly forL. baleicum, and we used transcriptomic profiling to compare adults and developing offspring from eusocial and solitary nests. We find that adult, reproductive females have similar expression profiles regardless of social structure in the nest, but that there are strong differences between reproductive females and workers from social nests. We also find substantial differences in the transcriptomic profiles of stage‐matched pupae from warmer, social‐biased sites compared to cooler, solitary‐biased sites. These transcriptional differences are strongly predictive of adult reproductive state, suggesting that the developmental environment may set the stage for adult behaviours inL. baleicum. Together, our results help to characterize the molecular mechanisms shaping variation in social behaviour and highlight a potential role of environmental tuning during development as a factor shaping adult behaviour and physiology in this socially flexible bee.

    

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