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The cuticular hydrocarbon (CHC) profile and the gut microbiome (GM) are crucial traits which have a significant impact on the life of bees. In honey bees, the CHC profile and the GM interact finely through trophallaxis, such that the characteristics of the GM are partially defined by the chemical recognition among sisters. However, most of the known primitively eusocial bees show simpler social traits, including moderate genetic relatedness among colony members, often due to workers' nest drifting or dispersal, and lack of trophallaxis. Hence, primitively eusocial bees offer a great opportunity to evaluate the respective role of worker‐worker genetic relatedness and of the environment in which the adult lives (residency nest) on the interaction between CHC profile and GM. Here, we investigated such relationships in the primitively eusocial digger bee Halictus scabiosae (Halictidae). We found a high rate of nest‐drifting by workers, which leads to a consequent highly variable intra‐colonial genetic relatedness. Genetically closely related workers, even occupying distant nests, did possess both a more similar microbiome profile and a more similar CHC profile. Additionally, sharing the same nest seemed to account for the similarity of both CHC profile and GM among workers. Interestingly, differences in microbiome profile and in CHC profile were highly and positively correlated across workers, even after controlling for genetic relatedness. The results of our study point towards an impact of genetic relatedness on the GM and the CHC profile, but also suggest that microbiome and CHC profile are partially acquired through adult nest environment, and that microbiome possibly has a role in shaping the cuticular chemistry. The relationship between cuticular hydrocarbon (CHC) profile and the gut microbiome (GM) is poorly known in bees. In the primitively eusocial bee Halictus scabiosae we found a high rate of nest‐drifting by workers, which leads to a consequent highly variable intra‐colonial genetic relatedness. Genetically closely related workers, even occupying distant nests, did possess both a more similar microbiome profile and a more similar CHC profile, and sharing the same nest seemed to also account for the similarity of both CHC profile and GM among workers.

Biodiversity is declining through human activities and urbanisation is often seen as a particular concern. Urban settings, however, provide diverse microclimatic conditions for plants and pollinating insects, and therefore may be significant habitats for the conservation of solitary and primitively eusocial bees, a major group of pollinators. This study analysed the interactions between these bees and the plants on which they forage, using a network approach. We compared urban habitats (gardens, roadsides, and open vegetation) in a large British town with nearby nature reserves. One native plant Taraxacum officinale (dandelion) was a core generalist species visited in all habitat types. Other core plant species restricted to particular habitats include species of Geranium , Bellis , Crepis , and Ranunculus . Two generalist bee species, Anthophora plumipes and Osmia bicornis were the core visitor species within the networks. The networks were comparatively more nested in urban habitat types than nature areas, suggesting more frequent interactions between generalist and specialist species in urban areas. Network connectance, network level specialisation (H 2 ’ index), and plant generality (network level) were not significantly different in urban and nature areas. However, visitor generality was found to be significantly higher in urban gardens than in nature areas. Careful management of common urban vegetation would be beneficial for supporting urban wild pollinators.

The benefits of cooperation are essential in driving group formation. However, an individual can gain significant benefits by acting selfishly at a substantial cost to others in the group. Thus, group members must find a balance between accepting and rejecting potential new members. Here, I explore the factors that mediate acceptance of non-related individuals during the period of group establishment in the primitively eusocial wasp Mischocyttarus mexicanus. In this species, group composition changes during establishment, with non-related females (non-nestmates) sometimes accepted into a foreign colony. By experimentally introducing non-nestmates to newly established colonies, I test the hypothesis that acceptance threshold of nestmates towards non-nestmates shifts depending on the ecological context, as predicted by the Optimal Acceptance Threshold Model. I explored how non-nestmate age (young vs. old), stage of colony establishment (early vs. late), initial behavior of the non-nestmates (non-aggressive vs. aggressive), and the behavioral response by nestmates (non-aggressive vs. aggressive) affected the rates of acceptance. My results show an effect of both non-nestmate age and stage of colony development on non-nestmate acceptance. Young non-nestmates were more frequently accepted in early than in late colonies. Late colonies more frequently rejected both young and old non-nestmates, suggesting a cost of accepting potential usurpers into late colonies. Surprisingly, non-nestmate aggressive behavior did not have a direct effect on their acceptance, but it triggered an aggressive response from nestmates. These findings reveal a shift in the acceptance threshold, suggesting an effect of the social context and the specific needs of a colony on non-nestmate acceptance.

Abstract Ropalidia marginata, traditionally regarded as a primitively eusocial wasp species appears to have acquired some features reminiscent of highly eusocial species. Queens are behaviorally passive individuals, yet maintain complete reproductive monopoly and probably use pheromones to achieve this. Regulation of worker foraging is achieved by the workers themselves in a decentralized, self-organized manner. If there are other species in the genus Ropalidia that do not show such relatively 'advanced' features, this genus can provide an attractive model system to investigate the evolutionary transition from the primitively eusocial to the highly eusocial state. Here, we therefore investigate the congeneric Ropalidia cyathiformis and demonstrate that in contrast to R. marginata, it appears to be a typical primitively eusocial species. As expected therefore, and in striking contrast with R. marginata, R. cyathiformis queens are the most, or among the most, dominant, active and interactive individuals and their behavior is consistent with the possibility that they suppress worker reproduction and regulate worker foraging in a relatively centralized manner. Upon removal of the queen, a potential queen with levels of aggression even higher than that of the queen, becomes apparent immediately. Such a potential queen appears to take over inhibition of worker reproduction and regulation of worker foraging by mechanisms similar to that used by the queen so that, there is no disruption in foraging and brood care. We suggest that comparative studies of

Caste determination in primitively eusocial sweat bees is thought to be due to an interacting suite of factors, including size of the larval provision mass, time of year, and social context of the nest into which a young female emerges. Newly emerged gynes are significantly fatter than newly emerged workers, suggesting the existence of larval caste determination cues. Since photoperiod, temperature, and interactions with nestmates were unlikely to affect larval caste determination, we compared the sizes and contents of larval provision masses destined to produce either workers or gynes. Gyne-destined larvae consumed pollen masses that were larger and contained slightly more sugar than those of worker-destined larvae. We suggest that sugar content is one cue which prompts the development of fat reserves in gyne-destined females but not in worker-destined females. The amount of fat possessed by a newly emerged female influences her chances of successfully entering diapause shortly after emergence. Therefore, small, lean females may be more susceptible to behavioural control by queens and more likely to become workers, while large, fat females would be more likely to become gynes.