Bumblebee Queens Research Articles

Examining the effects of repeated pesticide exposure on bumblebee queen survival and reproduction

Abstract Bees are key pollinators, and thus declines in their populations around the world may lead to negative consequences for both the environment and agricultural systems. While these declines are caused by multiple factors, the use of pesticides in agricultural systems has been identified as a key potential driver. Most bee species have an annual life cycle, with the potential for pesticide exposure throughout their life span. However, most studies have looked at a single exposure point within a season. Bumblebees, like most annual species, have an overwintering stage—which in their case is completed by bumblebee queens. Exposure to pesticides can be experienced by queens both before and after physiologically stressful periods such as hibernation and during nest foundation. This multi‐staged exposure may have increased impacts on bumblebee queens' colony foundation and reproductive output and therefore colony success. However, studies of such repeated exposures are lacking. Here, we look at the effects of an unstudied, yet biologically likely exposure regime. We exposed bumblebee queens to the insecticide sulfoxaflor at 65.5 ppb for 4 days both before and after hibernation, using a fullycrossed design, in order to assess the impact of such repeated exposure on survival and reproductive fitness. We observed queens through two important life stages, hibernation and colony foundation, following field realistic exposures to sulfoxaflor. We measured the effects on hibernation success, the likelihood of colony foundation and brood production. We found that neither exposure to sulfoxaflor pre‐ or post‐hibernation, nor their combination, impacted hibernation survival or colony foundation. Practical Implication: Our study is the first to highlight the repeated pesticide exposure bumblebee queens experience over different stages of their life cycle. Our results suggest that single or repeated exposure to dietary sulfoxaflor alone, albeit at a conservative field‐realistic profile, is unlikely to impact queen health at key points in their life cycle. Future studies should explicitly incorporate repeated exposure across life cycle stages when assessing the impacts of anthropogenic stressors on bee health.

Lack of thermal acclimation in multiple indices of climate vulnerability in bumblebees.

Indices of climate vulnerability are used to predict species' vulnerability to climate change based on intrinsic physiological traits, such as thermal tolerance, thermal sensitivity and thermal acclimation, but rarely is the consistency among indices evaluated simultaneously. We compared the thermal physiology of queen bumblebees between a species experiencing local declines (Bombus auricomus) and a species exhibiting continent-wide increases (B. impatiens). We conducted a multi-week acclimation experiment under simulated climate warming to measure critical thermal maximum (CTmax), critical thermal minimum (CTmin), the thermal sensitivity of metabolic rate and water loss rate and acclimation in each of these traits. We also measured survival throughout the experiment and after the thermal tolerance trials. Neither species acclimated to the temperature treatments by adjusting any physiological trait. We found conflicting patterns among indices of vulnerability within and between species. We also found that individuals with the highest CTmax exhibited the lowest survival following the thermal tolerance trial. Our study highlights inconsistent patterns across multiple indices of climate vulnerability within and between species, indicating that physiological studies measuring only one index of climate vulnerability may be limited in their ability to inform species' responses to environmental change.

No impact of cyantraniliprole on the hibernation success of bumble bees (Bombus terrestris audax) in a soil-mediated laboratory exposure study.

Increasing evidence shows that wild bees, including bumble bees, are in decline due to a range of stressors, including pesticides. Our knowledge of pesticide impacts has consequently grown to enable the design of increasingly realistic risk assessment methods. However, one area where knowledge gaps may still hinder our ability to assess the full range of bee-pesticide interactions is the field of exposure. Exposure has historically been linked to either direct contact with pesticides or the ingestion of contaminated pollen and nectar by bees. However, bumble bees, and other wild bees, may also be exposed to pesticides while using contaminated soil as an overwintering substrate. Yet knowledge of how soil-mediated exposure affects bumble bee health is lacking. Here we take one of the first steps towards addressing this knowledge gap by designing a method for testing the effects of soil-mediated pesticide exposure on bumble bee queen hibernation success. We measured hibernation survival, body weight change and abdominal fat content and found that none of these responses were affected by a field realistic soil exposure to the novel insecticide cyantraniliprole. Our study may help in developing a standardised method to test the effects of the soil-mediated pesticide exposure route in bumble bee queens.

Changes in bumblebee queen gut microbiotas during and after overwintering diapause.

Bumblebees are key pollinators with gut microbiotas that support host health. After bumblebee queens undergo winter diapause, which occurs before spring colony establishment, their gut microbiotas are disturbed, but little is known about community dynamics during diapause itself. Queen gut microbiotas also help seed worker microbiotas, so it is important that they recover post-diapause to a typical community structure, a process that may be impeded by pesticide exposure. We examined how bumblebee queen gut microbiota community structure and metabolic potential shift during and after winter diapause, and whether post-diapause recovery is affected by pesticide exposure. To do so, we placed commercial Bombus impatiens queens into diapause, euthanizing them at 0, 2 and 4 months of diapause. Additionally, we allowed some queens to recover from diapause for 1 week before euthanasia, exposing half to the common herbicide glyphosate. Using whole-community, shotgun metagenomic sequencing, we found that core bee gut phylotypes dominated queen gut microbiotas before, during and after diapause, but that two phylotypes, Schmidhempelia and Snodgrassella, ceased to be detected during late diapause and recovery. Despite fluctuations in taxonomic community structure, metabolic potential remained constant through diapause and recovery. Also, glyphosate exposure did not affect post-diapause microbiota recovery. However, metagenomic assembly quality and our ability to detect microbial taxa and metabolic pathways declined alongside microbial abundance, which was substantially reduced during diapause. Our study offers new insights into how bumblebee queen gut microbiotas change taxonomically and functionally during a key life stage and provides guidance for future microbiota studies in diapausing bumblebees.

Pesticide Contamination in Native North American Crops, Part II-Comparison of Flower, Honey Bee Workers, and Native Bee Residues in Lowbush Blueberry.

In lowbush blueberry fields, we conducted residue analysis comparing flowers, trapped pollen (honey bee and Osmia spp.), and collected bees (honey bee workers, bumble bee queens, and non-Bombus spp. wild native bees). The study was conducted from 2012 to 2014. The number of pesticide residues, total concentrations, and risk to honey bees (Risk Quotient) on flowers were not significantly different from those determined for trapped honey bee pollen (except in one study year when residues detected in flower samples were significantly lower than residue numbers detected in trapped pollen). The compositions of residues were similar on flowers and trapped pollen. The number of residues detected in honey bee pollen was significantly greater than the number detected in Osmia spp. pollen, while the total concentration of residue was not different between the two types of pollen. The risk to honey bees was higher in trapped honey bee pollen than in trapped Osmia spp. pollen. The analysis of honey bee workers, native bumble bee queens, and native solitary bees showed that although more pesticide residues were detected on honey bee workers, there were no differences among the bee taxa in total residue concentrations or risk (as estimated in terms of risk to honey bees).

Size-dependent responses of colony-founding bumblebee (Bombus impatiens) queens to exposure to pesticide residues in soil during hibernation

Bumblebees and other key pollinators are experiencing global declines, a phenomenon driven by multiple environmental stressors, including pesticide exposure. While bumblebee queens spend most of their life hibernating underground, no study to date has examined how exposure to pesticide-contaminated soils might affect bumblebee queens during this solitary phase of their lifecycle. We exposed Bombus impatiens queens (n = 303) to soil treated with field-realistic concentrations of two diamide insecticides (chlorantraniliprole and cyantraniliprole) and two fungicides (boscalid and difenoconazole), alone or combined, during a 30-week hibernation period. We found that exposure to boscalid residues in soil doubled the likelihood of queens surviving through the colony initiation period (after successful hibernation) and laying eggs. Our data also revealed complex interactions between pesticide exposure and queen body mass on aspects of colony founding. Among others, exposure to cyantraniliprole led to lethal and sublethal post-hibernation effects that were dependent on queen size, with larger queens showing higher mortality rates, delayed emergence of their first brood, and producing smaller workers. Our results show that effects of pesticide exposure depend on intrinsic traits of bumblebee queen physiology and challenge our understanding of how bees respond to pesticides under environmentally realistic exposure scenarios.

Metabolic Rate Suppression and Maintenance of Flight Muscle Metabolic Capacity during Diapause in Bumble Bee (Bombus impatiens) Queens.

AbstractThe common eastern bumble bee (Bombus impatiens) queens endure cold winter months by entering a diapause state. During this overwintering period, these animals use stored energy reserves while maintaining a low metabolic rate. This study investigates changes in the metabolic rate of bumble bee queens during diapause-like laboratory conditions and the potential reorganization of the flight muscle metabolic properties during this period. We first confirmed the hypometabolic state of queens during diapause in the laboratory, which lowered their resting metabolic rate to less than 5% of normal resting values. Body mass decreased during diapause, body composition changed where carbohydrates decreased initially, and later protein declined, with a similar trend for lipid content. Using cellular respirometry, we determined the capacity of the flight muscle cells of bumble bee queens to use various metabolic fuels and whether this capacity changes during the progression of diapause to favor stored lipid-derived substrates. Queens showed a low capacity to oxidize the amino acid proline, compared with workers, and their capacity to oxidize all metabolic substrates did not change during a 4-mo diapause period in the laboratory. We also show no detectable ability to oxidize fatty acid by flight muscle mitochondria in this species. The metabolic properties of flight muscle tissue were further characterized using metabolic enzyme activity profiles showing little change during diapause, indicating that profound metabolic suppression is induced without major changes in muscle metabolic phenotypes. Overall, B. impatiens queens undergo diapause while maintaining flight muscle capacity under the conditions used.

Unveiling the submerged secrets: bumblebee queens' resilience to flooding.

In a previous study, an experimental oversight led to the accumulation of water filling a container housing diapausing bumblebee queens. Surprisingly, after draining the water, queens were found to be alive. This observation raises a compelling question: can bumblebee queens endure periods of inundation while overwintering underground? To address this question, we conducted an experiment using 143 common eastern bumblebee (Bombus impatiens) queens placed in soil-filled tubes and subjected to artificially induced diapause in a refrigerated unit for 7 days. Tap water was then added to the tubes and queens (n = 21 per treatment) were either maintained underwater using a plunger-like apparatus or left to float naturally on the water's surface for varying durations (8 h, 24 h or 7 days) while remaining in overwintering conditions. Seventeen queens served as controls. After the submersion period, queens were removed from water, transferred to new tubes with soil and kept in cold storage for eight weeks. Overall, queen survival remained consistently high (89.5 ± 6.4%) across all treatments and did not differ among submersion regimes and durations. These results demonstrate the remarkable ability of diapausing B. impatiens queens to withstand submersion under water for up to one week, indicating their adaptations to survive periods of flooding in the wild.

Investigating trade-offs between ovary activation and immune protein expression in bumble bee (Bombus impatiens) workers and queens.

Evidence for a trade-off between reproduction and immunity has manifested in many animal species, including social insects. However, investigations in social insect queens present a conundrum: new gynes of many social hymenopterans, such as bumble bees and ants, must first mate, then transition from being solitary to social as they establish their nests, thus experiencing confounding shifts in environmental conditions. Worker bumble bees offer an opportunity to investigate patterns of immune protein expression associated with ovary activation while minimizing extraneous environmental factors and genetic differences. Here, we use proteomics to interrogate the patterns of immune protein expression of female bumble bees (Bombus impatiens) by (i) sampling queens at different stages of their life cycle, then (ii) by sampling workers with different degrees of ovary activation. Patterns of immune protein expression in the haemolymph of queens are consistent with a reproduction-immunity trade-off, but equivalent samples from workers are not. This brings into question whether queen bumble bees really experience a reproduction-immunity trade-off, or if patterns of immune protein expression may actually be due to the selective pressure of the different environmental conditions they are exposed to during their life cycle.

Notes sur la nidification spontanée de reines sauvages de bourdons en Belgique (Hymenoptera : Apidae)

Notes about spontaneous nesting of bumblebees’ queens in Belgium (Hymenoptera: Apidae). - To develop a rearing system for different wild bumblebee species, we experimented techniques for spontaneous nesting of wild queens. Our nest devices, which contain mouse litter as substrate, are used to attract wild bumblebee queens in search of a nest and to initiate brood construction. Over a total of four years of observation, we have installed 57 call nests with a 44 % success rate of nest initiation. However, this method has some limitations and does not show satisfactory results for ground-nesting bumblebee species.

Application of 3D-printed pollen traps as a useful tool for exposure and risk assessment of pesticide residues on bumblebees

The study was designed to test the feasibility of using 3D-printed pollen traps for long-term monitoring of Bombus terrestris colonies' exposure to pesticide residues in pollen loads collected by them, along with an assessment of the resulting risks to the bumblebee's adults, larvae, and queens. Bumblebee colonies were placed in the vicinity of flowering orchards, winter oilseed rape, allotments, or home gardens for 6 weeks of the experiment. Pollen traps printed in 3D technology were installed in the hive inlets. The weight of bumblebee pollen loads obtained using pollen traps was in the range of 0.036–5.83 g. Pollen load samples were analyzed for residues of up to 261 pesticides and their metabolites by liquid and gas chromatography techniques coupled to tandem mass spectrometry (LC-MS/MS and GC-MS/MS). Residues of 18 fungicides, 12 herbicides, 6 insecticides, and an acaricide were detected. Herbicide – pendimethalin, fungicide – thiophanate-methyl, and insecticide – chlorpyrifos-ethyl were the most commonly detected pesticides. Chlorpyrifos and thiacloprid residues were detected in pollen load samples in the next year after their ban from use as plant protection products in the European Union. The risk of acute or chronic effects was assessed as negligible or low, although the chronic risk of bumblebee queens to insecticide chlorpyrifos and the acute risk of larvae exposed to acaricide fenpyroximate could be interpreted as moderate. The risk of sublethal effects related to chronic exposure of adult bumblebees and queens to pollen loads contaminated by chlorpyrifos-ethyl and cypermethrin cannot be excluded. The risk of chronic toxicity or sublethal effects may be particularly relevant for bumblebee queens, especially during their foraging in the initial period of establishing a new colony.

Untargeted Lipidomics Analysis Unravels the Different Metabolites in the Fat Body of Mated Bumblebee (Bombus terrestris) Queens.

The fat body has important functions in energy, fertility, and immunity. In female insects, mating stimulates physiological, behavioral, and gene expression changes. However, it remains unclear whether the metabolites in the fat body are affected after the bumblebee (Bombus terrestris) queen mates. Here, the ultrastructure and lipid metabolites in fat body of mated queens were compared with those of virgins. The fat body weight of mated bumblebee queens was significantly increased, and the adipocytes were filled with lipid droplets. Using LC-MS/MS-based untargeted lipidomics, 949 and 748 differential metabolites were identified in the fat body of virgin and mated bumblebee queens, respectively, in positive and negative ion modes. Most lipid metabolites were decreased, especially some biomembrane components. In order to explore the relationship between the structures of lipid droplets and metabolite accumulation, transmission electron microscopy and fluorescence microscopy were used to observe the fat body ultrastructure. The size/area of lipid droplets was larger, and the fusion of lipid droplets was increased in the mated queen's fat body. These enlarged lipid droplets may store more energy and nutrients. The observed differences in lipid metabolites in the fat body of queens contribute to understanding the regulatory network of bumblebees post mating.

Uncovering the role of juvenile hormone in ovary development and egg laying in bumble bees

Juvenile hormone (JH) regulates developmental and physiological processes in insects. In bumble bees, the hormone acts as a gonadotropin that mediates ovary development, but the exact physiological pathways involved in ovary activation and subsequent egg laying are poorly understood. In this study, we examine how queen hibernation state, caste, and species impact the gonadotropic effect of JH in bumble bee queens through methoprene (JH analogue) application. We extend previous research by assessing queen egg laying and colony initiation, alongside ovary development. Furthermore, we compared sensitivity of workers of both species to the juvenile hormone's gonadotropic effect. In both bumble bee species, the ovaries of hibernated queens were developed five to six days after breaking diapause, regardless of methoprene treatment. By contrast, methoprene did have a stimulatory effect on ovary development in non-hibernated queens. The dose needed to obtain this effect was higher in B. impatiens. Methoprene did not have gonadotropic effects in callow workers of both species. These results indicate that the physiological effect of exogenous methoprene application varies according to species, caste and hibernation status. Interestingly, despite gonadotropic effects in non-hibernated queens, oviposition was not accelerated by JH. This suggests that JH alone is insufficient to induce egg laying and that an additional stimulus, which is naturally present in hibernated queens, is required. Consequently, our findings indicate that other physiological processes, beyond a rise in JH alone, are required for oviposition and colony initiation.

Parental care behaviour in bumble bee queens is tightly regulated by the number of helpers in incipient nests

Parental care behaviour in bumble bee queens is tightly regulated by the number of helpers in incipient nests

Costs of reproduction are present but latent in eusocial bumblebee queens

BackgroundThe standard evolutionary theory of ageing proposes that ageing occurs because of a trade-off between reproduction and longevity. Eusocial insect queens exhibit positive fecundity-longevity associations and so have been suggested to be counter-examples through not expressing costs of reproduction and through remodelling conserved genetic and endocrine networks regulating ageing and reproduction. If so, eusocial evolution from solitary ancestors with negative fecundity-longevity associations must have involved a stage at which costs of reproduction were suppressed and fecundity and longevity became positively associated. Using the bumblebee (Bombus terrestris), we experimentally tested whether queens in annual eusocial insects at an intermediate level of eusocial complexity experience costs of reproduction, and, using mRNA-seq, the extent to which they exhibit a remodelling of relevant genetic and endocrine networks. Specifically, we tested whether costs of reproduction are present but latent, or whether a remodelling of relevant genetic and endocrine networks has already occurred allowing queens to reproduce without costs.ResultsWe experimentally increased queens’ costs of reproduction by removing their eggs, which caused queens to increase their egg-laying rate. Treatment queens had significantly reduced longevity relative to control queens whose egg-laying rate was not increased. Reduced longevity in treatment queens was not caused by increased worker-to-queen aggression or by increased overall activity in queens. In addition, treatment and control queens differed in age-related gene expression based on mRNA-seq in both their overall expression profiles and the expression of ageing-related genes. Remarkably, these differences appeared to occur principally with respect to relative age, not chronological age.ConclusionsThis study represents the first simultaneously phenotypic and transcriptomic experimental test for a longevity cost of reproduction in eusocial insect queens. The results support the occurrence of costs of reproduction in annual eusocial insects of intermediate social complexity and suggest that reproductive costs are present but latent in queens of such species, i.e. that these queens exhibit condition-dependent positive fecundity-longevity associations. They also raise the possibility that a partial remodelling of genetic and endocrine networks underpinning ageing may have occurred in intermediately eusocial species such that, in unmanipulated conditions, age-related gene expression depends more on chronological than relative age.

First field-based estimates of bumblebee diapause survival rates showcase high survivorship in the wild.

Bumblebee (Bombus spp.) queens overwintered in artificial settings tend to have low survival rates, raising concerns that diapause may be a particularly sensitive life cycle stage for this ecologically and economically valuable group of pollinators. However, it remains unclear whether lab-based estimates of diapause survival are comparable to survival rates of natural populations. In this study, we monitored the survival of Bombus impatiens queens overwintering in the field in Ipswich, MA, and conducted a meta-analysis of studies that estimate queen diapause survival in the lab to compare our field-based estimates of survival to those of lab-based studies. We found that queen B. impatiens had relatively high rates of overwintering survival after about six months (> 60%), especially when compared to estimates of six-month survival from lab studies (< 10%). We also observed a trend that broadly corroborates many lab studies of bumblebees, in that overwinter survival of queens was related to colony origin. In addition to providing the first estimate of diapause survival for bumblebee queens in nature, our study emphasizes the need to verify patterns observed in the lab to field-based studies. Although protecting target species during sensitive life cycle stages is a fundamental goal of conservation ecology, it is first necessary to identify at what stages of the life cycle populations are most vulnerable. Our results suggest that, at least in some study systems, diapause survival of queen bumblebees in the field may be higher than suggested by lab studies. The online version contains supplementary material available at 10.1007/s10841-023-00478-8.

Nutrient enrichment and rainfall affect plant phenology and floral resource availability for pollinators

Wild pollinators are critical to maintaining ecosystem services and facilitating crop production, but habitat degradation and resource loss are leading to worldwide pollinator declines. Nutrient enrichment and changes in rainfall due to global warming are drivers of global environmental change, and likely to impact pollinator foraging behavior and reproductive success through changes to the growth and phenology of flowering plants. Here, we provide a short review of pollinator conservation in the context of nutritional ecology and plant-pollinator interactions. Then, we present novel research into the effects of nutrient and rainfall variation on plant phenology. In this study, we experimentally manipulated the amount of water and supplemental nutrients available to wild sunflower (Helianthus annuus) and goldenrod (Solidago spp.) throughout their growing season. We evaluated how changes in growth and bloom time could impact resource availability for bumble bee (Bombus impatiens) queens preparing to overwinter. We found that fertilizer and rainfall alter plant bloom time by 2–18 days, though flowering response was species-specific. Fertilizer did not significantly affect plant growth or number of flowers produced when plants were grown under drought conditions. When water was not limiting, fertilized sunflowers bloomed in floral pulses. These findings carry important implications for growers and land managers, providing insight into potential drivers of wild pollinator decline and possible conservation strategies.

A review of factors influencing diapause in bumble bee queens

A review of factors influencing diapause in bumble bee queens

Contrasting effects of landscape on nest founding and colony success of bumble bees in a mixed‐crop agroecosystem

Abstract Nest‐founding bumble bee queens search landscapes broadly for a nest site, whose later‐developed workers are constrained to foraging around the nest. Landscape could therefore have different influences on nest site selection and subsequent colony success. Additionally, the density of bumble bees in a landscape reflects the product of their nest density and nest success. To examine separate landscape effects on nest density and success, we examined nest occupancy (reflecting nest density) and colony size (reflecting nest success) using ground‐installed nest boxes placed adjacent to blueberry (Vaccinium corymbosum) fields in the Lower Mainland of British Columbia, Canada. Nest‐searching queens occupied 59% of these boxes. We classified landscapes in a 1.5 km radius of colonies using habitats of a priori relevance to bumble bees: beneficial (i.e. flowering) agriculture, non‐beneficial agriculture (NBA), forest, open semi‐natural, suburban, and their configuration (habitat edge density). Landscape strongly affected nest founding but only weakly affected colony success. Nest founding increased in landscapes with more forest habitat, more open semi‐natural habitat (and little NBA), and more habitat edge (and little NBA). Colony success increased in landscapes with more edge density (and much NBA). Overall, edge habitats enhanced bumble bee populations, but enhancement was conditional: edge increased nest occupation in landscapes with little NBA and nest success in landscapes with a lot of NBA. Populations of crop‐pollinating bumble bees might therefore best be enhanced by locally enhancing nesting: protecting forests, 2D semi‐natural habitats (when flowering crops are uncommon), and edge habitats.

Impact of climate change on parasite infection of an important pollinator depends on host genotypes.

Climate change is predicted to affect host-parasite interactions, and for some hosts, parasite infection is expected to increase with rising temperatures. Global population declines of important pollinators already have been attributed to climate change and parasitism. However, the role of climate in driving parasite infection and the genetic basis for pollinator hosts to respond often remain obscure. Based on decade-long field data, we investigated the association between climate and Nosema bombi (Microsporidia) infection of buffed-tailed bumblebees (Bombus terrestris), and whether host genotypes play a role. For this, we genotyped 876 wild bumblebee queens and screened for N. bombi infection of those queens between 2000 and 2010. We recorded seven climate parameters during those 11 years and tested for correlations between climate and infection prevalence. Here we show that climatic factors drive N. bombi infection and that the impact of climate depends on mitochondrial DNA cytochrome oxidase I (COI) haplotypes of the host. Infection prevalence was correlated with climatic variables during the time when queens emerge from hibernation. Remarkably, COI haplotypes best predict this association between climatic factors and infection. In particular, two host haplotypes ("A" and "B") displayed phenotypic plasticity in response to climatic variation: Temperature was positively correlated with infection of host haplotype B, but not haplotype A. The likelihood of infection of haplotype A was associated with moisture, conferring greater resistance to parasite infection during wetter years. In contrast, infection of haplotype B was unrelated to moisture. To the best of our knowledge, this is the first study that identifies specific host genotypes that confer differential parasite resistance under variable climatic conditions. Our results underscore the importance of mitochondrial haplotypes to ward off parasites in a changing climate. More broadly, this also suggests that COI may play a pertinent role in climate change adaptations of insect pollinators.