Bombus Research Articles

Bumble bees do not avoid field-realistic but innocuous concentrations of cadmium and copper.

Bee populations are facing numerous stressors globally, including environmental pollution by trace metals and metalloids. Understanding whether bees can detect and avoid these pollutants in their food is pivotal, as avoidance abilities may mitigate their exposure to xenobiotics. While these pollutants are known to induce sublethal effects in bees, such as disrupting physiological mechanisms, their potential impacts on locomotive abilities, fat metabolism, and reproductive physiology remain poorly understood. In this study, utilising workers of the buff-tailed bumble bee and two prevalent trace metals, namely cadmium and copper, we aimed to address these knowledge gaps for field-realistic concentrations. Our findings reveal that workers did not reject field-realistic concentrations of cadmium and copper in sucrose solutions. Moreover, they did not reject lethal concentrations of cadmium, although they rejected lethal concentrations of copper. Additionally, we observed no significant effects of field-realistic concentrations of these metals on the walking and flying activities of workers, nor on their fat metabolism and reproductive physiology. Overall, our results suggest that bumble bees may not avoid cadmium and copper at environmental concentrations, but ingestion of these metals in natural settings may not adversely affect locomotive abilities, fat metabolism, or reproductive physiology. However, given the conservative nature of our study, we still recommend future research to employ higher concentrations over longer durations to mimic conditions in heavily polluted areas (i.e., mine surrounding). Furthermore, investigations should ascertain whether field-realistic concentrations of metals exert no impact on bee larvae.

Stable pollinator communities in different white clover populations suggest potential win-win scenarios for crop yield and biodiversity

Compared to monocultures, intercropping systems offer many agronomic benefits, including higher yield stability. In this study, we assessed whether cropping systems that are beneficial for yield stability are also beneficial for pollinator communities and whether the effect is modulated by the landscape type. Using a replicated block design in one heterogeneous and one homogeneous agricultural landscape, we studied the pollinator communities in eight populations (i.e., genotypes) of white clover (Trifolium repens) grown as a monoculture or as a two-species mixture (together with perennial ryegrass, Lolium perenne) or three-species mixture (together with perennial ryegrass and chicory, Cichorium intybus). We recorded 1486 honey bees and 1254 wild pollinators belonging to 46 species. Bumble bees were the most abundant wild pollinators (49.6 %), followed by hover flies (23.4 %), and non-Bombus wild bees (21.5 %). Lepidoptera accounted for only 5.4 % of the wild pollinators. We found a higher species richness and abundance of wild pollinators in monocultures than in two-species mixtures, but white clover population did not influence pollinators. Moreover, species richness and abundance were also higher in the homogeneous landscape than in the heterogenous one. Most species were foraging on white clover. However, 18 species (39.1 %, n = 18/46) were recorded foraging on chicory and/or weeds, and ten of these wild pollinator species were never recorded on white clover. Our study highlights that diverse pollinator communities require both abundant floral resources and diverse plant communities, that their needs are not in conflict with the goal of achieving yield stability, and that the landscape type can modulate the effect of the cropping system. Moreover, the lack of pollinator preference for different white clover populations suggests that farmers can select mixtures that enhance yield stability without negatively affecting pollinator communities. Overall, these results highlight that intercropping systems comprising several plant species and plant genotypes can guarantee yield stability without compromising the pollinator community, showing that win-win situations for farmers and biodiversity are possible.

The Hole Truth: Why Do Bumble Bees Rob Flowers More Than Once?

Primary nectar-robbers feed through holes they make in flowers, often bypassing the plant's reproductive organs in the process. In many robbed plants, multiple holes are made in a single flower. Why a flower should be robbed repeatedly is difficult to understand: a hole signals that a nectar forager has already fed, which would seem likely to predict low rewards. We tested three explanations for this pattern in Corydalis caseana (Fumariaceae), a bumble bee pollinated and robbed plant: (1) multiple holes appear only after all flowers have been robbed once; (2) individual foragers make multiple holes during single visits; and (3) it is more profitable for bees to rob older flowers, even if they have already been robbed. We tested these hypotheses from 2014 to 2016 in a Colorado, USA population using data on robbing rates over time, floral longevity, nectar accumulation in visited and unvisited flowers, and the accumulation of robbing holes across the life of flowers. Multiple holes were already appearing when two-thirds of flowers still lacked a single hole, allowing us to reject the first hypothesis. The second hypothesis cannot offer a full explanation for multiple robbing holes because 35% of additional holes appeared in flowers one or more days after the first hole was made. Repeated sampling of bagged and exposed inflorescences revealed that flowers filled at a constant rate and refilled completely after being drained. Consequently, young flowers are of consistently low value to foragers compared to older flowers even if they had previously been robbed, consistent with the third hypothesis. While further studies are needed, these results offer a simple explanation for the paradoxical clustering of nectar-robbing damage in this and possibly other plant species.

Multiscale spatial analysis of two plant–insect interactions: effects of landscape, resource distribution, and other insects

ContextBiotic resource exploitation is a critical determinant of species’ distributions. However, quantifying resource exploitation patterns through space and time can be difficult, complicating their incorporation in spatial ecology studies. Therefore, understanding the local drivers of spatial patterns of resource exploitation may contribute to better large-scale species distribution models.ObjectivesWe investigated (1) how the resource exploitation patterns of two trophic interactions (plant–insect) are explained by insect behaviour, resource aggregation, and potential insect-insect interactions. We also analyzed how (2) resource patch size and (3) resource accessibility in a heterogeneous landscape affected host exploitation patterns.MethodsWe quantified nectar robbing by insects in the genus Bombus (bumblebees) and seed predation by Brachypterolus vestitus larvae (Antirrhinum beetle) on Antirrhinum majus L. (wild snapdragons) in the Pyrenees Mountains, Catalonia, Spain. We tested hypotheses about resource exploitation by integrating spatial analyses at multiple scales.ResultsBoth trophic interactions were aggregated, explained by the aggregation of their resource. At some scales, nectar robbing is more aggregated than the resource. Trophic interaction abundance is proportional to resource patch size, following the ideal free distribution model. Landscape features do not explain the locations exploited. Nectar robbing and seed predation occur together more often than expected.ConclusionsOur findings suggest that multiple biotic and ecological spatial factors may simultaneously affect resource exploitation at a local scale. These findings should be considered when developing agricultural projects, management plans and conservation policies.

Genotypic variation in blueberry flower morphology and nectar reward content affects pollinator attraction in a diverse breeding population

BackgroundPollination is crucial to obtaining optimal blueberry yield and fruit quality. Despite substantial investments in seasonal beekeeping services, blueberry producers consistently report suboptimal pollinator visitation and fruit set in some cultivars. Flower morphology and floral rewards are among the key factors that have shown to contribute to pollinator attraction, however little is known about their relative importance for improving yield in the context of plant breeding. Clarifying the relationships between flower morphology, nectar reward content, pollinator recruitment, and pollination outcomes, as well as their genetic components, can inform breeding priorities for enhancing blueberry production. In the present study, we measured ten flower and nectar traits and indices of successful pollination, including fruit set, seed count, and fruit weight in 38 southern highbush blueberry genotypes. Additionally, we assessed pollinator visitation frequency and foraging behavior over two growing seasons. Several statistical models were tested to optimize the prediction of pollinator visitation and pollination success, including partial least squares, BayesB, ridge-regression, and random forest.ResultsRandom forest models obtained high predictive abilities for pollinator visitation frequency, with values of 0.54, 0.52, and 0.66 for honey bee, bumble bee, and total pollinator visits, respectively. The BayesB model provided the most consistent prediction of fruit set, fruit weight, and seed set, with predictive abilities of 0.07, -0.08, and 0.42, respectively. Variable importance analysis revealed that genotypic differences in nectar volume had the greatest impact on honey bee and bumble bee visitation, although preferences for flower morphological traits varied depending on the foraging task. Flower density was a major driving factor attracting nectar-foraging honey bees and bumble bees, while pollen-foraging bumble bees were most influenced by flower accessibility, specifically corolla length and the length-to-width ratio.ConclusionsHoney bees comprised the majority of pollinator visits, and were primarily influenced by nectar volume and flower density. Corolla length and the length-to-width ratio were also identified as the main predictors of fruit set, fruit weight, seed count, as well as pollen-foraging bumble bee visits, suggesting that these bees and their foraging preferences may play a pivotal role in fruit production. Moderate to high narrow-sense heritability values (ranging from 0.30 to 0.77) were obtained for all floral traits, indicating that selective breeding efforts may enhance cultivar attractiveness to pollinators.

Lethal effects and sex-specific tolerance of copper and cadmium in the buff-tailed bumble bee

Exposure to environmental pollutants, including trace metals, is a major driver of bee decline worldwide. While pesticides undergo standardised risk assessments (i.e., LD50) and the implementation of online databases, no such approaches exist for trace metals. Here, using acute oral exposure, we determined the LC50, LD50, and mass-standardised LD50 of copper and cadmium, essential and non-essential metals, respectively, in workers and males of the buff-tailed bumble bee. We also evaluated gut damage and sucrose consumption in workers post-exposure. Cadmium was more toxic than copper for workers at same doses, although both metals induced severe gut melanisation and reduced sucrose consumption at high concentrations. Males displayed higher tolerance to cadmium, but it was correlated to their higher body mass, emphasising the necessity for reporting mass-standardised LD50 for genuine sex comparisons in risk assessments. Our findings advocate for the establishment of databases focusing on metal-induced lethal effects on model bee species.

Targeted viromes and total metagenomes capture distinct components of bee gut phage communities

BackgroundDespite being among the most abundant biological entities on earth, bacteriophage (phage) remain an understudied component of host-associated systems. One limitation to studying host-associated phage is the lack of consensus on methods for sampling phage communities. Here, we compare paired total metagenomes and viral size fraction metagenomes (viromes) as methods for investigating the dsDNA viral communities associated with the GI tract of two bee species: the European honey bee Apis mellifera and the eastern bumble bee Bombus impatiens.ResultsWe find that viromes successfully enriched for phage, thereby increasing phage recovery, but only in honey bees. In contrast, for bumble bees, total metagenomes recovered greater phage diversity. Across both bee species, viromes better sampled low occupancy phage, while total metagenomes were biased towards sampling temperate phage. Additionally, many of the phage captured by total metagenomes were absent altogether from viromes. Comparing between bees, we show that phage communities in commercially reared bumble bees are significantly reduced in diversity compared to honey bees, likely reflecting differences in bacterial titer and diversity. In a broader context, these results highlight the complementary nature of total metagenomes and targeted viromes, especially when applied to host-associated environments.ConclusionsOverall, we suggest that studies interested in assessing total communities of host-associated phage should consider using both approaches. However, given the constraints of virome sampling, total metagenomes may serve to sample phage communities with the understanding that they will preferentially sample dominant and temperate phage.6S3bFgh36a8k5RNed1PpF4Video

Consumption of pollen contaminated with field-realistic concentrations of fungicide causes sublethal effects in Bombus impatiens (Hymenoptera: Apidae) microcolonies.

Bumble bees are declining across the globe. The causes of this decline have been attributed to a variety of stressors, including pesticides. Fungicides are a type of pesticide that has been understudied in the context of bumble bee health. As a result, fungicides are often applied to flowering plants without consideration of pollinator exposure. Recent work demonstrates that fungicides have sublethal effects in bumble bees, but little is known about how much fungicide it takes to cause these sublethal effects. To address this gap in the literature, we fed microcolonies of the common eastern bumble bee (Bombus impatiens CressonHymenoptera: ApidaeHymenoptera: ApidaeHymenoptera: ApidaeHymenoptera: Apidae) pollen contaminated with a range of fungicide concentrations. We chose these concentrations based on the range of fungicide concentrations in pollen and nectar that were reported in the literature. Results revealed that later-stage pupae and newly emerged males are potentially sensitive to fungicide exposure, showing smaller size and reduced fat reserves at intermediate levels of contamination. Compared to the control, intermediated levels of fungicide-contaminated pollen led to increased pupal mortality and delayed male emergence. Contrary to expectations, higher fungicide levels did not exhibit a linear relationship with negative impacts, suggesting nuanced effects. Because body size and emergence timing are important aspects of bumble bee reproductive behavior, results have implications for mating success, potentially disrupting colony development.

Bumble Bees of Florida

Bumble Bees of Florida

Mating frequency estimation and its importance for colony abundance analyses in eusocial pollinators: a case study of Bombus impatiens (Hymenoptera: Apidae).

The genus Bombus (bumble bees) includes approximately 265 species, many of which are in decline in North America and Europe. To estimate colony abundance of bumble bees in natural and agricultural habitats, sibship relationships are often reconstructed from genetic data with the assumption that colonies have 1 monandrous queen. However, some species such as the North American common eastern bumble bee (Bombus impatiens Cresson) can display low levels of polyandry, which may bias estimates of colony abundance based on monandrous sibship reconstructions. To accurately quantify rates of polyandry in wild and commercially mated queens of this species, we empirically estimated mating frequencies using a novel statistical model and genotypes from 730 bees. To genotype individuals, we used a highly polymorphic set of microsatellites on colonies established from 20 wild-caught gynes and 10 commercial colonies. We found multiple fathers in 3 of the wild colonies and 3 of the commercial colonies. This resulted in average effective mating frequencies of 1.075 ± 0.18 and 1.154 ± 0.25 for wild and commercial colonies, respectively. These findings agree with previous reports of low rates of polyandry for B. impatiens. Using a large empirical dataset, we demonstrate that assuming monandry for colony abundance estimation in species that violate this assumption results in an overestimation of the number of colonies. Our results emphasize the importance of studying mating frequencies in social species of conservation concern and economic importance for the accuracy of colony abundance estimation and for understanding their ecology and sociobiology.

The role of landscape factors in shaping bumble bee pathogen loads across regions of the eastern Nearctic

Abstract Pathogens and parasites are drivers of declines in bumble bees. Their levels can be influenced by numerous abiotic and biotic factors, thus managing disease in these bees requires understanding the relative impact of these factors on pathogen loads. We evaluated loads of black queen cell virus (BQCV) and deformed wing virus in bumble bees (Bombus impatiens) and honey bees (Apis mellifera), and loads of parasites Vairimorpha bombi and Crithidia bombi in B. impatiens, from sites varying in habitat type and quality across North Carolina, USA. Pathogen loads were assessed against metrics for land cover, floral quality, bee diversity and weather. Results were compared against similar data from Pennsylvania, USA, and other landscape studies on bumble bees in North America. Spatial variation in pathogen loads was lower in bumble bees in North Carolina than in Pennsylvania, which reduced the power to detect landscape effects. For example, Crithidia was fairly ubiquitous and Vairimorpha was not detected. Data from both states revealed that developed land and honey bees were most consistently positively correlated with viral loads, especially for BQCV, whereas forest and nesting habitat availability were often negatively correlated with loads. Multivariate models only supported a positive relationship between summer floral resources and BQCV loads in North Carolina bumble bees. Together with the broader literature, these data indicate that levels of developed land and honey bees are most associated with increased pathogen loads while floral availability and bee community composition show more context‐dependent effects.

Warming summer temperatures are rapidly restructuring North American bumble bee communities.

A rapidly warming climate is driving changes in biodiversity worldwide, and its impact on insect communities is critical given their outsized role in ecosystem function and services. We use a long-term dataset of North American bumble bee species occurrences to determine whether the community temperature index (CTI), a measure of the balance of warm- and cool-adapted species in a community, has increased given warming temperatures. CTI has increased by an average of 0.99°C in strong association with warming maximum summer temperatures over the last 30 years with the areas exhibiting the largest increases including mid- to high latitudes as well as low and high elevations-areas relatively shielded from other intensive global changes. CTI shifts have been driven by the decline of cold-adapted species and increases in warm-adapted species within bumble bee communities. Our results show the pervasive impacts and ecological implications warming temperatures pose to insects.

Insect pollinators: The time is now for identifying species of greatest conservation need

AbstractSevere declines in the abundance of insects, including economically and ecologically important pollinators, are alarming conservationists and the public. Yet despite these increasingly well‐documented declines, relatively few pollinating insects other than butterflies, moths, and bumble bees have appeared as Species of Greatest Conservation Need (SGCN) in State Wildlife Action Plans, decadal‐scale blueprints for wildlife conservation efforts across the United States that require updating in 2025. Species absent from SGCN lists are ineligible for congressionally appropriated State Wildlife Grants that direct millions of dollars annually for their conservation. In the past, knowledge about the distribution and abundance of many insect pollinators was too poor to identify those meeting state guidelines for inclusion as SGCN. Using case studies from 4 northeastern states, we demonstrate that sufficient conservation status data now exist for many pollinators, including bees, butterflies, moths, beetles, and flower flies, to identify at‐risk species meriting inclusion on SGCN lists in many states. Doing so will increase funding for surveys, habitat protection and enhancement, and other conservation activities that will benefit this vitally important guild.

Infection by Crithidia bombi increases relative abundance of Lactobacillus spp. in the gut of Bombus terrestris.

Gut microbial communities confer protection against natural pathogens in important pollinators from the genera Bombus and Apis. In commercial species B. terrestris and B. impatiens, the microbiota increases their resistance to the common and virulent trypanosomatid parasite Crithidia bombi. However, the mechanisms by which gut microorganisms protect the host are still unknown. Here, we test two hypotheses: microbiota protect the host (1) through stimulation of its immune response or protection of the gut epithelium and (2) by competing for resources with the parasite inside the gut. To test them, we reduced the microbiota of workers and then rescued the microbial community by feeding them with microbiota supplements. We then exposed them to an infectious dose of C. bombi and characterised gene expression and gut microbiota composition. We examined the expression of three antimicrobial peptide genes and Mucin-5AC, a gene with a putative role in gut epithelium protection, using qPCR. Although a protective effect against C. bombi was observed in bumblebees with supplemented microbiota, we did not observe an effect of the microbiota on gene expression that could explain alone the protective effect observed. On the other hand, we found an increased relative abundance of Lactobacillus bacteria within the gut of infected workers and a negative correlation of this genus with Gilliamella and Snodgrassella genera. Therefore, our results point to a displacement of bumblebee endosymbionts by C. bombi that might be caused by competition for space and nutrients between the parasite and the microbiota within the gut.

Exploring machine learning in the context of environmental usage prediction

The use of environmental prediction refers to predicting the impact that human activity will have on ecosystems, natural resources and other environmental factors in the future. This strategy looks at historical patterns, present situations and future predictions to hypothesize about the ecological effects of human activities, climate change and other factors. This research suggests machine learning(ML) techniques to predict environmental uses. Prediction accuracy declinesover time and models face challenges due to the need for observable data integration in sectors like agriculture, energy and waterfor successful sub-seasonal predictions. To tackle these issues, we proposed a Next Generation Bumble Bee Mating Optimized Naïve Bayes Algorithm (NGBBMO-NBA) method that is used to enhance weather prediction. The research gathers the SSF dataset to make predictions on the usage of the environment. We use a min-max normalization approach for data preprocessing. The principalcomponent analysis (PCA) method extracts features from the SSF data. Environmental uncertainty inhibits sub-seasonal projections. Our suggested method, NGBBMO-NBA, surpasses the current techniques for ecological prediction in terms of energy consumption (96.5%), F1-Score (96%), Mean Absolute Error (MAE) (97) and Root Mean Square Error (RMSE) (98.5).

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).

Challenges and opportunities in the adoption of entomological pollination of tomato (Solanum lycopersicum L.) by bumblebees in vertical farms: a comprehensive review

The present study aims to analyze, based on bibliographic sources, the possibility of using bumblebees (genus Bombus) in the pollination of tomato plants (Solanum lycopersicum L.) in vertical farms, as well as their advantages and costs. The work includes the definition of vertical farms and their structures, the description of tomato pollination methods in nature, comparisons between different pollination methods in the vertical farming system, cost analyses, and characteristics of these bees that allow their adaptation in enclosed environments with the use of artificial lighting. Considering the high costs in these systems, the hypothesis of using entomological pollination as an alternative to reduce costs is justified. The review was conducted systematically, searching academic databases for relevant articles, theses, and reports on entomological pollination in vertical farms. In conclusion, it can be observed that these bees, besides being excellent pollinators, can possibly adapt to the characteristic conditions of a vertical farm. However, the behavior of these insects within this system has been poorly studied, with many opportunities and topics in this area that can serve as a starting point for future experiments.

Chromosome-Level Assembly and Annotation of the Genome of the Endangered Giant Patagonian Bumble Bee Bombus dahlbomii.

This article describes a genome assembly and annotation for Bombus dahlbomii, the giant Patagonian bumble bee. DNA from a single, haploid male collected in Argentina was used for PacBio (HiFi) sequencing, and Hi-C technology was then used to map chromatin contacts. Using Juicer and manual curation, the genome was scaffolded into 18 main pseudomolecules, representing a high-quality, near chromosome-level assembly. The sequenced genome size is estimated at 265 Mb. The genome was annotated based on RNA sequencing data of another male from Argentina, and BRAKER3 produced 15,767 annotated genes. The genome and annotation show high completeness, with >95% BUSCO scores for both the genome and annotated genes (based on conserved genes from Hymenoptera). This genome provides a valuable resource for studying the biology of this iconic and endangered species, as well as for understanding the impacts of its decline and designing strategies for its preservation.

A wireless, remotely operable and easily customizable robotic flower system

Abstract Understanding the complex interactions between external and internal factors that influence pollinator foraging behaviour is essential to understand ecosystem functioning, design agricultural practices or develop effective conservation strategies. However, it remains challenging to collect large and reliable data sets with reasonable personnel and workload. In this study, we present a wireless and cost‐effective robotic flower equipped with internet of things (IoT) technology that automatically offers nectar to visiting insects while monitoring visitation time and duration. The robotic flower is easy to manipulate and settings such as nectar refill rates can be remotely altered, making it ideal for field settings. The system transmits data completely wirelessly and autonomously, is mobile and easy to clean. The prototype settings allow for approximately 2 weeks of uninterrupted data collection for each battery charge. As a proof‐of‐concept application, a foraging preference dual choice experiment with bumblebees was performed. On average, more than 7000 flower visits per colony were registered daily with a set‐up consisting of 16 robotic flowers. The data show a gradual preference shift away from the pre‐trained low concentration, confirming the hypothesis of favouring sugar water with higher concentration. The robotic flower provides accurate and reliable data on insect behaviour, significantly reducing the price and/or labour costs. Although primarily designed for (bumble)bees, the system could be easily adapted for other flower‐visiting insects. The robotic flower is user‐friendly and can be easily adapted to address a wide range of research questions in pollination ecology, conservation biology, biocontrol and ecotoxicology, and allows for detailed studies on how nectar traits, flower colour and shape or pollutants affect foraging behaviour.

Bumble bees lose more water when it's drier and hotter

Bumble bees lose more water when it's drier and hotter