Bumblebees are key pollinators in agricultural and natural ecosystems; however, climate change is driving shifts in population size, body size, and diversity. Accelerating global warming affects bumblebee body size, thereby influencing the strength of sexual selection and overall population fitness. Thus, this study aimed to investigate the effects of body mass and temperature on sexual selection in Bombus terrestris reared under warm conditions, with mating conducted between equal sex ratios at both optimal (23 °C) and elevated (32 °C) temperatures. Mating success was lower at 32 °C than at 23 °C, regardless of body mass; however, larger queens and males consistently exhibited higher mating success at both temperatures than their smaller counterparts. Mate-choice patterns were similar across temperatures: large queens predominantly mated large males, whereas small ones mainly mated small males. However, small queens tended to mate large males at 32 °C than at 23 °C. Meanwhile, matings between small queens and small males occurred relatively later at both temperatures. Although small males exhibited longer mating durations than large ones, the amount of sperm transferred to the spermathecae of the queens was positively associated with the body size of both males and queens. Our findings indicate that, at equal sex ratios, mate choice in bumblebees is primarily determined by body mass at all temperatures. Thus, smaller bumblebees associated with higher temperatures had the lowest mating success.
Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of molybdenum in form of a chelate with EDTA as a nutritional feed additive for honeybees and bumblebees. The FEEDAP Panel concludes that additive MoNa is safe for honeybees and bumblebees at the maximum recommended use level of 8 mg/hive per feeding, according to the conditions of use. The use of the additive in animal nutrition is safe for the consumer and the environment. The additive should be considered a skin and respiratory sensitiser. Inhalation and dermal exposure are considered a risk and should be minimised. The additive is not irritant to skin nor to eyes. The FEEDAP Panel cannot conclude on the efficacy of the additive MoNa as a nutritional additive in honeybees and bumblebees. However, the Panel concludes that the supplementation of MoNa at 8 mg/hive has the potential to be efficacious as a zootechnical additive for honeybees. No conclusion can be reached on the efficacy of the additive when supplemented to bumblebees.
Pollinators, especially native bumblebees, are critical to maintaining ecosystem function and food production by enabling essential plant-pollinator interactions. Yet, these keystone species are increasingly threatened by habitat degradation, climate change, and competitive pressure from managed honey bees, whose expansion poses ecological risks. This is particularly urgent in regions where biodiversity conservation and commercial beekeeping intersect. Iran's Zagros and Alborz mountain ranges, recognized as global biodiversity hotspots, harbor rich native flora and support 26 species of native bumblebees essential to sustaining ecological integrity. These regions also underpin Iran's position as the world's third-largest honey producer, highlighting a delicate balance between pollinator conservation and apicultural expansion. While many bumblebee species are globally listed as vulnerable, endangered, or in decline, their conservation status and population trends in Iran remain undocumented, raising concern about unmonitored local declines. To address this gap, we applied an ensemble species distribution modeling approach integrating bioclimatic, NDVI, topographic, and anthropogenic variables to predict habitat suitability and assess spatial overlap between native bumblebees and managed honey bees. Results reveal high-suitability zones for native bumblebees in the Alborz Mountains, Azerbaijan highlands, and western Zagros. Although nationwide overlap is moderate, localized hotspots of intense co-occurrence, particularly in Alborz, signal zones of competitive conflict and ecological vulnerability. Most managed honey bees in Iran belong to Apis mellifera carnica, which is not native to Iran. The native Iranian honey bee is Apis mellifera meda. As non-native, high-density, human-supported species, managed honey bees may intensify pressure on native pollinators, especially under accelerating climate and land-use change. This study provides spatial evidence to guide conservation priorities and align biodiversity protection with sustainable apiculture across one of the world's most vital mountain ecosystems.
Rapid learning of aversive stimuli is adaptive, but the persistence of the avoidance response in the absence of further reinforcement might depend on the severity of the adverse experience. For example, an experience involving injury would be expected to lead to more durable memory than the mere exposure to an unpleasant tastant, especially when new experiences indicate that the aversive stimulus is no longer present. We investigated how bumblebees (Bombus terrestris) learn and retain associations between flower colours and two types of aversive stimuli: electric shock and saturated salt (NaCl) solution. Using a conditioning paradigm, we examined how these stimuli influence avoidance learning across foraging bouts and tracked the process of extinction learning, the formation of new memory in response to the absence of the reinforcement, over two weeks. Our results show that bees rapidly learn to avoid both stimuli, and reach >90% accuracy of avoidance after six foraging bouts. We then examined how bees modified their avoidance behaviour in the absence of further aversive stimulation. Testing extinction learning on days 1, 3, 5, 7 and 14, we found that electric shock as a nociceptive stimulus induces a more persistent avoidance response, whereas exposure to the salt by engaging gustatory aversion pathways leads to a three times faster extinction rate. This suggests that although the initial training leads to equal levels of avoidance for both stimuli, bumblebees might display greater behavioural flexibility when updating the association between a colour and an unpleasant taste in comparison to a potentially injurious stimulus.
Sex role differences can influence ecological and evolutionarily important traits like activity level and behavioural flexibility. In bumblebees, female workers are the main foragers for the colony, whereas males (drones) have minimal responsibility. However, males become solitary foragers once they leave the colony, suggesting that increased activity level and behavioural flexibility are crucial for their survival. Here, we conducted a laboratory experiment to compare male and female bumblebees’ active time in a novel environment (using an ‘activity’ task) as well as their colour-reward associative learning ability and behavioural flexibility (with a simultaneous two-choice discrimination-reversal colour learning task). As predicted, males were more active in the novel environment than females. Males and females showed comparable performance in learning the colour-reward association, but males demonstrated enhanced behavioural flexibility when the reward contingency changed. Males’ active time may reflect their exploratory behaviour (e.g., pre-mating patrolling), and their enhanced flexibility suggests their readiness to find new profitable flowers when exploited flowers decrease in quality. These results highlight the importance of these behavioural and cognitive traits for males, which may increase their chance of finding mates and improve their foraging efficiency. The online version contains supplementary material available at 10.1007/s10071-026-02061-5.
Bumblebees are excellent pollinators sustaining ecosystems, however, their populations are declining due to land-use changes, lack of food resources, and pathogen-induced diseases. The gut microbiota is central to animal health, influencing nutrition and defense. We examined how pollen diet affects colony development, pathogen presence, and gut microbiota in two native South American bumblebee species, Bombus pauloensis and B. bellicosus. In B. pauloensis, monofloral pollen from Eucalyptus grandis increased worker body mass and showed a slight reduction in developmental time compared to polyfloral pollen. In B. bellicosus, no significant diet effects on body mass or development time were observed. Diet also altered gut microbiota structure. Based on diversity analyses, significant diet-associated shifts were observed in B. pauloensis queens and B. bellicosus workers. In B. pauloensis queens, monofloral pollen increased bacterial richness and favored Snodgrassella spp., whereas in B. bellicosus workers, monofloral pollen also increased diversity, but enriched ASVs were mainly environmental taxa. The microsporidian pathogen Nosema ceranae was detected in a single B. pauloensis colony, limiting conclusions about prevalence or diet. These findings demonstrate that nutritional quality of dietary pollen and/or pollen diversity modulates gut microbiota and colony development in native bumblebees, with species and caste-specific responses. Our study suggests a potential role of nutrition in host-microbiota interactions and indicates that agricultural intensification and the loss of floral diversity may affect bee health. By linking pollen nutritional quality/diversity, microbiota structure, and colony performance, these findings may help inform pollinator-friendly landscape management and could contribute to improving the resilience of South American agroecosystems.
Pollinator decline is one of the most urgent environmental challenges of our time, and pesticide use is considered a major contributing factor. In this study, we investigated whether exposure to volatilized prallethrin, a widely used insecticide, impairs the homing ability of bumblebees. Using a consumer-grade vaporizing device, we exposed foraging bees to field-realistic doses of prallethrin and then tested their ability to return to their colony in a rural area where they were already familiar with the surroundings. Our results show that longer exposure durations reduced the bees' return rates, indicating disrupted navigational ability. However, among those that did return, homing time was not affected by the treatment. While our study only focuses on one key behavioural trait, the findings provide clear evidence of a sublethal effect of a commonly used household insecticide on an essential pollinator species.
Judgement bias tasks are increasingly used to assess affective states in animals, yet the extent to which they might reflect transient states or stable traits remains unclear. Here, we tested bumblebees (Bombus terrestris) in an active choice task across three repeated sessions to assess individual consistency in the absence of any manipulation. Bees were trained to associate each of two colours with either a high or a low reward, presented in separate chambers. During testing, they were presented with ambiguous colours. Bees were more likely to choose the high-reward chamber and to choose more quickly in response to colours closer to the positive colour. The latency to choose the cues showed significant and moderate repeatability across sessions, suggesting a stable, trait-like underlying component. In contrast, the repeatability of the chamber choices was negligible, indicating that such responses might be largely state-dependent and influenced by situational factors. These findings suggest that judgement biases, particularly as assessed through an active choice task, reflect states affected by external factors. Active choice tasks may help disentangle stable behavioural traits from transient affective states in invertebrates.
Could bumblebees have emotional states that can be transferred between individuals? A recent study provides positive evidence and illustrates the logic and methods employed to investigate these challenging questions.
Attention in vertebrates helps prioritise the processing of important sensory information and filter out irrelevant signals. The capture of attention by sudden or salient stimuli is typically called bottom-up attention. Little is known about similar attentional processes in insects, although they should be advantageous for insects as well. We therefore adapted two paradigms used to investigate bottom-up attention in primates to investigate it in bumblebees: a target detection task and a target discrimination task. For both tasks, we trained bees to choose between two locations on each side of a computer screen and collect a reward below a full contrast target displayed on the screen. During detection task tests, the contrast of the target was varied, and it could be preceded by a cue flashed on the side of the target, the opposite side of the screen or not flashed at all. The discrimination task tests were similar but with a full contrast target on one side and a variable contrast distractor on the opposite side of the screen. We tested if the presence of the flash influenced the orientation and choices of the bees as well as their contrast sensitivity as has been seen in primates. We analysed bee choices using both direct observation of their behaviours at the trained locations and a trajectory analysis of high-speed videos. Our results show no effect of the prior cue, suggesting that other paradigms might prove more useful to test these processes in insects. The online version contains supplementary material available at 10.1007/s10905-026-09908-2.
As global warming intensifies, pollinators such as bumblebees may experience increasing exposure to temperatures near their thermal limits. Heat stress impairs foraging and survival, making it essential to understand bumblebee body temperature in natural conditions. This study tested the feasibility of using infrared (IR) thermography as a non-invasive technique to measure the thoracic temperature of wild, foraging bumblebees and to evaluate how body temperature relates to environmental variables, including ambient air and floral surface temperatures. Thermographic measurements were validated against internal thoracic temperatures recorded by thermocouples in static bees, revealing a strong correlation (r = 0.98) with an average absolute difference of <1 °C. We analysed thermal images of live Bombus individuals (n = 98) collected over five observation days in late summer. Bee body temperatures routinely exceeded both ambient and floral temperatures and approached the critical thermal maximum (CTmax) during midday foraging. A linear mixed-effects model revealed that bee temperature increased significantly with both ambient air and floral temperature, and a significant interaction term indicated that warmer floral surfaces amplified the effect of high ambient temperatures. These findings demonstrate that IR thermography can reliably measure bumblebee body temperature in-situ, bridging the gap between laboratory-derived thermal limits and field conditions. By capturing the combined effects of microclimate and physiology, this method offers new insight into pollinator heat stress at the organismal level and highlights the importance of fine-scale thermal data for assessing species' responses to climate change.
Insecticides and herbicides are utilized worldwide in agricultural practices, and these hazardous materials retained in the environment impose potential threats to pollinators, including bumblebees. However, whether and how short-term exposure to sublethal concentrations of insecticide/herbicide induces lasting toxicity effects in newly emerged gynes remain uncharacterized. In this study, we comprehensively investigated the long-term consequences of short-term exposure to sublethal imidacloprid (IMI) and glyphosate (GLY) (singly or combined) on bumblebee (Bombus terrestris) gynes under different exposure regimens through integrated physiological and transcriptomic analyses. Short-term exposure of gynes to IMI alone and IMI + GLY mixtures not only impacted survival, tissue development, nutrient reserves, mating, diapause energy metabolism, and reproduction of queens but also caused transgenerational toxicity affecting offspring development and performance. In contrast, GLY exposure alone adversely affected tissue development, nutrient reserves, diapause energy metabolism, and offspring development of queens. Notably, compared to direct exposure, starvation exacerbated the adverse effects of IMI exposure on queens' diapause survival and energy metabolism and aggravated the impacts of GLY exposure on gynes' ovarian development and lipid reserves. For combined IMI + GLY exposure, starvation mainly amplified physiological disturbances related to queens' diapause survival, energy metabolism, and offspring development and performance. The observed defects in short-term IMI- and IMI + GLY-exposed gynes may result from altered nutrient metabolic pathways. Collectively, our research unveils the lasting toxicity of short-term mixed insecticide/herbicide exposure on gynes/queens and their offspring from physiological and molecular perspectives, underscoring the urgent need for regulatory consideration of combined pesticide risks in bumblebee conservation.
Male bees navigate complex tradeoffs between energy acquisition and reproductive signaling, yet their movement strategies remain understudied. Unlike workers that optimize foraging to support the colony, male bumblebees (Bombus terrestris) forage independently to collect nectar and deposit sex pheromones on selected plants. Using high-resolution 3D tracking in an indoor flight cage, we investigated how the spatial arrangement of nectar and scent-marking sites, along with nectar availability, influence male movement patterns. We manipulated the distribution of feeders (artificial flowers) and scent-marking locations (branches), and varied nectar delivery rates, to assess effects on foraging, scent-marking, and patrolling. Males responded strongly to spatial structure: in clumped arrays with evenly spaced resources, movements between consecutive visits were shorter and more localized, while in dispersed arrays with irregular spacing, transitions were longer and more variable. The combination of dispersed spacing and low nectar availability imposed the highest foraging demands, resulting in fewer feeding events and reduced total feeding time. Despite these increased costs, males maintained consistent investment in reproductive behaviors, suggesting a prioritization of mate-seeking over energy gain. Rather than reducing signaling, males adjusted their foraging strategy-favoring fewer but prolonged feeding bouts when nectar availability allowed. These findings reveal a unidirectional behavioral adjustment, in which foraging is modulated to sustain reproductive effort, and show how spatial resource structure and nectar availability together shape movement decisions in male pollinators.
The regulation of reproductive division of labor in eusocial insects is pivotal for the evolution of social behavior and the maintenance of eusociality. Primitively eusocial bumblebee workers retain reproductive totipotency, with dominant workers capable of ovarian activation and egg-laying. Here, we investigated the cellular and molecular basis of reproductive hierarchy in Bombus terrestris by constructing a single-nucleus transcriptomic atlas of the ovary in queenless bumblebee groups. Using single-nucleus RNA sequencing, we profiled ovarian cell types and revealed that α-worker bees possess more mature follicle cells, which are essential for ovarian development. Differential maturation of follicle cells, particularly at the vitellogenic stage, emerges as a key regulatory node in this process. More mature follicle cells promote the production of growth factors that activate PDK1. This activation subsequently induces AKT phosphorylation and downstream signaling. As a result, the levels of 20-hydroxyecdysone are elevated in dominant α-workers. By demonstrating how follicle cell maturation and signaling drive reproductive activation, our findings link cellular physiology to social organization and provide new insight into the molecular mechanisms underlying the evolution of eusociality.
Invasive species may exhibit shifts in their gut microbiome in response to novel environments and diet, but this may differ across host species and their time since colonisation. We investigate if site environmental variables and foraged pollen resources differentially shape the gut microbiomes of two bee species with contrasting introduction histories: The European honeybee, Apis mellifera (introduced 1831), and the recently invasive bumblebee, Bombus terrestris (invaded 1992). Using landscape-scale metabarcoding across the island state of Tasmania in Australia, we characterised gut bacteria (16S rRNA) and corbicular pollen diversity (ITS2) for each species. Gut bacterial composition was significantly associated with mean annual temperature for A. mellifera and with mean annual precipitation and percentage of pasture for B. terrestris. In B. terrestris, the core and facultative gut microbial diversity and richness showed associations with precipitation, foraged pollen diversity, wind velocity and temperature. Foraged pollen diversity of native plants more strongly predicted the facultative gut microbiome across species. Overall, the gut microbiome of B. terrestris showed a stronger response to abiotic and biotic predictors compared to A. mellifera. Our findings advance understanding of how environmental and dietary factors shape pollinator gut microbiomes at landscape scales, with implications for pollinator health and survival.
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[This corrects the article DOI: 10.1111/eva.70234.].
Bumblebees rely on diverse sensory information to locate flowers while foraging. The majority of research exploring the relationship between visual and olfactory floral cues is performed at local spatial scales and applicable to understanding floral selection. Floral-cue use during search remains underexplored. This study investigates how the bumblebee Bombus impatiens uses visual versus olfactory information from flowers across behavioral states and spatial scales. At local spatial scales, non-flying animals in an associative learning paradigm will generalize to either unimodal attribute of a learned color+odor cue with equal likelihood. However, bumblebees flying in a wind tunnel shift cue-use strategy depending on the spatiotemporal scale of cue encounter. When both color and odor cues mimic local/ within patch spatial scale, bumblebees weigh color information of a learned floral-cue more heavily. When cues mimic an intermediate/ between patch spatial scale, bumblebees weigh color and odor information equally, and show the highest response to fully intact multimodal cues. Thus the spatiotemporal scale of sensory information influences how bumblebees utilize multimodal floral cues.
Biological invasions can disrupt plant-pollinator interactions by altering pollinator behaviour and pollen transfer dynamics, yet the mechanisms and timing of these effects remain poorly understood. Most studies rely on observational comparisons or removal experiments in long-established invasions, but little is known about changes in pollination function at the onset of invasion. We investigated the pollination of Stachys sylvatica by combining field comparisons between pristine and invaded sites with an experimental introduction of Impatiens glandulifera into a previously uninvaded site. We quantified pollinator visitation, pollen loads carried by bumblebees, and conspecific and invasive pollen deposition on S. sylvatica stigmas. Across multiple field sites, stigmas of S. sylvatica in pristine habitats received approximately three times more conspecific pollen than those in invaded sites. Bumblebees dominated the pollinator assemblage across all sites, and in invaded habitats, they carried pollen loads strongly dominated by I. glandulifera. During the experimental introduction, bumblebees rapidly incorporated I. glandulifera into their foraging, while conspecific pollen deposition on S. sylvatica stigmas declined sharply, with 81.5% reduction within 4 days. Our results demonstrate that invasion by I. glandulifera can rapidly impair pollination function of a co-flowering native species through changes in pollen transport and transfer efficiency, even before strong shifts in visitation patterns become apparent. By capturing early invasion dynamics through experimental introduction, this study highlights the importance of direct pollen-based metrics for understanding how plant invasions disrupt pollination processes.
Insect pollinators, such as bumblebees, are commonly used to facilitate pollination in strawberry greenhouses. To ensure effective pollination, this study monitored the entry and exit behaviour of bumblebees around the nest box using an industrial camera. Video footage was captured, and a virtual cube-shaped frame was positioned at the entrance of the nest box. Bumblebee detection and counting within this virtual frame were performed using two methods: a) YOLO only and b) YOLO with a simple algorithm. In the algorithm-based method, if a bumblebee crossed the virtual frame an odd number of times, it was classified as having entered or exited the nest box. Conversely, an even number of crossings indicated that the bumblebee had either turned back or re-entered without exiting. The proposed method allowed for the automated counting of bumblebees entering and exiting a nest box. Compared to the YOLO-only method, the proposed method significantly improved performance metrics, including accuracy, precision, and F1 score. The proposed method can effectively support the monitoring of pollinator behaviour in strawberry greenhouses.