Global warming threatens wild bees and their interaction with plants. While earlier studies have highlighted the negative effects of elevated temperatures on bee-plant interactions, we still lack knowledge about how they impact the foraging behaviours that are central to bee pollination activities. To address this knowledge gap, we investigated how ambient temperature affected the foraging behaviours of the bumblebee Bombus terrestris. We allowed the bumblebees to forage freely on artificial flowers in two climate-controlled rooms set at 24°C and 32°C. The colonies were alternated between the two temperatures every week. We recorded the flower visitation rate, flight speed, total foraging time and number of foraging trips. In addition, we measured flight metabolic rate across a range of temperatures to assess its potential as an underlying mechanism. In comparison to 24°C, at 32°C, flower visitation time decreased while flower visitation rate and flight speed increased. This is consistent with the reduction in flight metabolic rate recorded between these temperatures. At 32°C, the number of trips made by each worker decreased, suggesting that, despite the reduced energetic cost, flight in elevated temperatures may be stressful. Our results suggest that elevated temperatures affect bumblebee foraging behaviour and that this would likely disrupt plant-insect interactions.

Eusocial insect colonies act as a superorganism, which can improve their ability to buffer the negative impact of some anthropogenic stressors. However, this buffering effect can be affected by anthropogenic factors that reduce their colony size. A reduction in colony size is known to negatively affect several parameters like brood maintenance or thermoregulation, but the effects on behaviour and cognition have been largely overlooked. It remains unclear how a sudden change in group size, such as that which might be caused by anthropogenic stressors, affects individual behaviour within a colony. In this study, the bumblebee Bombus terrestris was used to study the effect of social group size on behaviour by comparing the associative learning capabilities of individuals from colonies that were unmanipulated, reduced to a normal size (a colony of 100 workers) or reduced to a critically low but functional size (a colony of 20 workers). The results demonstrated that workers from the different treatments performed equally well in associative learning tasks, which also included no significant differences in the learning capacity of workers that had fully developed after the colony size manipulation. Furthermore, we found that the size of workers had no impact on associative learning ability. The learning abilities of bumblebee workers were thus resilient to the colony reduction they encountered. Our study is a first step towards understanding how eusocial insect cognition can be impacted by drastic reductions in colony size. Significance statement While anthropogenic stressors can reduce the colony size of eusocial insects, the impact of this reduction is poorly studied, particularly among bumblebees. We hypothesised that colony size reduction would affect the cognitive capacity of worker bumblebees as a result of fewer social interactions or potential undernourishment. Using differential conditioning, we showed that drastic reductions in colony size have no effect on the associative learning capabilities of the bumblebee Bombus terrestris and that this was the same for individuals that were tested just after the colony reduction and individuals that fully developed under the colony size reduction. We also showed that body size did not affect learning capabilities. This resilience could be an efficient buffer against the ongoing impacts of global change.

Stingless bees are important pollinators of wild and cultivated plants, and they produce medicinal honey. However, their taxonomy and systematics are still debated and would benefit a continent-wide revision. Here, we explore the potential of wing shape in delineation and classification of Afrotropical Meliponini using geometric morphometrics. We sampled 749 specimens from nine countries of sub-Saharan Africa, belonging to the genera Meliponula (n = 8), Dactylurina (n = 2) and Plebeina (n = 1). Specimens collected from Kenya were used as standards to assess similar species collected from other eight African countries. Eleven landmarks were plotted on the right forewing of each specimen to conduct multivariate analyses and group/specimen classification. Our results show that seven out of eleven African stingless bee species were reliably discriminated using wing shape, however, there was overlap in the remaining four species, namely Meliponula cameroonensis, Meliponula ferruginea, Meliponula togoensis and Meliponula erythra. In conclusion geometric morphometrics represent a promising taxonomic tool that can be applied to identify African stingless bee species. 

The impact of global warming on wild bee decline threatens the pollination services they provide. Exposure to temperatures above optimal during development is known to reduce adult body size but how it affects the development and scaling of body parts remains unclear. In bees, a reduction in body size and/or a reduction in body parts, such as the antennae, tongue and wings, and how they scale with body size (i.e. their allometry) could severely affect their fitness. To date, it remains unclear how temperature affects body size and the scaling of morphological traits in bees. To address this knowledge gap, we exposed both males and workers of Bombus terrestris to elevated temperature during development and assessed the effects on (i) the size of morphological traits and (ii) the allometry between these traits. Colonies were exposed to optimal (25°C) or stressful (33°C) temperatures. We then measured the body size, wing size, antenna and tongue length, as well as the allometry between these traits. We found that workers were smaller and the antennae of both castes were reduced at the higher temperature. However, tongue length and wing size were not affected by developmental temperature. The allometric scaling of the tongue was also affected by developmental temperature. Smaller body size and antennae could impair both individual and colony fitness, by affecting foraging efficiency and, consequently, colony development. Our results encourage further exploration of how the temperature-induced changes in morphology affect functional traits and pollination efficiency. 

Global warming has been identified as one of the main drivers of population decline in insect pollinators. One aspect of the insect life cycle that would be particularly sensitive to elevated temperatures is the developmental transition from larva to adult. Temperature-induced modifications to the development of body parts and sensory organs likely have functional consequences for adult behaviour. To date, we have little knowledge about the effect of sub-optimal temperature on the development and functional morphology of different body parts, particularly sensory organs, in ectothermic solitary pollinators such as butterflies. To address this knowledge gap, we exposed the pupae of the butterfly Pieris napi to either 23 degrees C or 32 degrees C and measured the subsequent effects on eclosion, body size and the development of the wings, proboscis, eyes and antennae. In comparison to individuals that developed at 23 degrees C, we found that exposure to 32 degrees C during the pupal stage increased mortality and decreased time to eclose. Furthermore, both female and male butterflies that developed at 32 degrees C were smaller and had shorter proboscides, while males had shorter antennae. In contrast, we found no significant effect of rearing temperature on wing and eye size or wing deformity. Our findings suggest that increasing global temperatures and its corresponding co-stressors, such as humidity, will impact the survival of butterflies by impairing eclosion and the proper development of body and sensory organs.

Body size is a trait that can affect plant–pollinator interaction efficiency and plant reproductive success. We explored the impact of intraspecific size shifts on the interactions between pollinators and flowering plants under controlled conditions. We considered two development conditions leading to the production of large and small individual flowers of Borago officinalis and Echium plantagineum. We also used the natural variability of worker size within bumblebee colonies to isolate small and large workers. We performed a fully crossed experiment with the two flower sizes of each plant species and the two sizes of bumblebee workers. Our results show that the size of both partners did not affect bee foraging behavior in most of the evaluated parameters and both bee sizes were equally efficient in depositing pollen. Significant differences were found only in pollen deposition across the life of a flower in small flowers of B. officinalis, with the greatest quantity of pollen deposited by small bees. We did not find a relationship between pollinator size and plant fitness. Our results suggest that generalist plant–pollinator interactions may be resilient to future potential mismatches in the size of the partners but remain to be tested if they are still resilient under the new environmental conditions resulting from global changes.

Foraging behavior is driven by diverse factors, notably life history traits. Foraging strategies are particularly complex among eusocial species such as bumblebees, because they depend primarily on the needs of the colony, rather than on individual's needs. Colony size, i.e. the number of workers in a colony vary a lot among eusocial insects. While a large colony can be adaptive, several drivers can strongly decrease colony size, like pesticides or high temperatures. In this study, we used the bumblebee Bombus terrestris to assess if workers adapted their foraging behavior to such rapid decreases in colony size. We conducted the foraging experiments with two plant species commonly used by bumblebees: Borago officinalis and Echium plantagineum. Several foraging parameters were measured: foraging time, number of foraging trips, number of workers foraging, handling time and visiting rate. Despite a drastic reduction in colony size, nearly all the foraging behavior parameters were unaffected by the colony size reduction. Colonies that were subject to a large decrease in workers instead displayed high resilience and behavioral plasticity by quickly increasing the proportion of foragers. Ultimately, further research should assess if this consistency in foraging behavior also allows bumblebee colonies to maintain both the efficiency of the resources collection and pollination.

Climate change impacts on insect pollinators has largely focused on changes in abundance and range, yet pollination capacity also relies on ability to acquire, process and respond to information. We argue for the urgent need to focus on these largely overlooked processes by describing how insect sensory ecology and behaviour are afected by temperature and highlighting key knowledge gaps that should be addressed.

Safeguarding crop pollination services requires the identification of the pollinator species involved and the provision of their ecological requirements at multiple spatial scales. However, the potential for agroecological intensification of pollinator-dependent crops by harnessing pollinator diversity is limited by our capacity to characterise the community of pollinator species for each crop, and to determine how it is influenced by the different survey methods used, as well as by climatic variables at larger geographic scales. Here, we surveyed wild bees using a standardised protocol at an unprecedented scale including 62 commercial apple orchards in Western and Central Europe (i) to validate recent findings on pollinator community divergence as measured by common survey methods (netting and pan trapping) using conventional and alternative biodiversity metrics (phylogenetic and functional diversity), and (ii) to investigate the impact of climatic variation on the patterns observed. Our results confirm the significant divergence in pollinator communities measured using the two common methods at the larger, sub-continental scale, and we provide evidence for a significant influence of climate on the magnitude of pollinator community divergence (beta diversity and its turnover component) be-tween survey methods, particularly when comparing colder to warmer sites and regions. We also found that warmer sites are more dissimilar than colder sites in terms of species composition, functional traits, or phylo-genetic affinities. This result probably stems from the comparatively larger species pool in Southern Europe and because apple flowers are accessible to a wide spectrum of pollinator species; hence, two distant survey localities in Southern Europe are more likely to differ significantly in their pollinator community. Collectively, our results demonstrate the spatially-varying patterns of pollinator communities associated with common survey methods along a climate gradient and at the sub-continental scale in Europe.

Bee foraging behavior provides a pollination service that has both ecological and economic benefits. However, bee population decline could directly affect the efficiency of this interaction. Among the drivers of this decline, global warming has been implicated as an emerging threat but exactly how increasing temperatures affect bee foraging behavior remains unexplored. Here, we assessed how exposure to elevated temperatures during development affects the foraging behavior and morphology of workers from commercial and wild Bombus terrestris colonies. Workers reared at 33 °C had a higher visiting rate and shorter visiting time than those reared at 27°C. In addition, far fewer workers reared at 33 °C engaged in foraging activities and this is potentially related to the drastic reduction in the number of individuals produced in colonies exposed to 33 °C. The impact of elevated developmental temperature on wild colonies was even stronger as none of the workers from these colonies performed any foraging trips. We also found that rearing temperature affected wing size and shape. Our results provide the first evidence that colony temperature can have striking effects on bumblebee foraging behavior. Of particular importance is the drastic reduction in the number of workers performing foraging trips, and the total number of foraging trips made by workers reared in high temperatures. Further studies should explore if, ultimately, these observed effects of exposure to elevated temperature during development lead to a reduction in pollination efficiency.