Aura Palonen

Biological invasions may induce adaptive shifts in traits that increase individual reproductive success, thereby accelerating population growth and amplifying ecological impacts. One such trait is polyandry, i.e. multiple mating by females, which may vary between endemic and invasive populations due to variation in demographic and environmental factors that alter the costs and benefits of multiple mating. Despite polyandry being widespread across taxa, comparative studies among multiple endemic and invasive populations of invasive species remain scarce. Here, we estimated the prevalence of polyandry in two endemic and five invasive populations of small hive beetle ( Aethina tumida ), a globally invasive parasite affecting bee health. Using DNA microsatellite genotyping of field-sampled females and their offspring to estimate mating frequencies, we show that polyandry varies in SHB populations and females mate with 1–13 males. However, the polyandry levels were not significantly different across the endemic and invasive populations compared. These results suggest that polyandry in SHB may be a stable reproductive trait rather than a plastic response to invasion-related factors. Our work supports further research on how multiple mating may improve both individual reproductive success and population viability in the context of biological invasions.

Eusocial insect colonies can choose different behaviours to combat the same parasites. While honeybee (HB), Apis mellifera , colonies remove eggs and larvae of parasitic small hive beetles (SHB), Aethina tumida , they encapsulate adults in propolis. It is currently unknown whether there is flexibility in this system. Here, we show encapsulation of eggs by colonies as an alternative to removal. Oviposition sites with or without SHB eggs were introduced into HB field colonies of mixed European origin. After 24 h, sites were removed to measure the propolised area and to quantify the remaining eggs. Further, SHB egg laying depth, and HB worker proboscis length and thickness, were measured. Even though the proboscises were long enough to reach most eggs, the number of eggs before and after introduction did not differ. Instead, HB used more propolis on sites with eggs compared to controls. This suggests decision making by colonies for either egg removal or encapsulation and demonstrates considerable flexibility in social immunity. Such flexibility probably contributes to eusocial insect resilience and calls for efforts to understand colony decision making.

High infestation levels of small hive beetle (SHB), Aethina tumida , can cause more damage to honeybee, Apis mellifera , host colonies. However, the spatiotemporal variation of SHB infestations is poorly understood. Here, we show that SHB infestations can be equally high in native and invasive ranges, suggesting that differences between host populations are the key criterion for damage. The data reveal that spatial variation within locations was not correlated with migratory beekeeping, SHB management strategies, nor the number of colonies at an apiary. Despite no annual changes in SHB infestations, the data confirm seasonal variation in infestations in two locations probably due to environmental factors affecting SHB. Infestations are lower in Italy than elsewhere, possibly due to strongly implemented management strategies. It is apparent that our understanding of varying SHB infestations is still limited. This suggests that further efforts are required to elucidate our knowledge of this important host-parasite system.