Nesting biology and social organisation of a silk wasp (Microstigmus rosae) from the North–West Ecuadorian Choco

Abstract

Microstigmus Ducke (Hymenoptera, Apoidea, Crabronidae, Pemphredoninae) is an intriguing genus of wasp, particularly interesting for the study of social evolution as it contains the only species of apoid wasps known to exhibit eusocial behaviours. Thus far, data concerning the genetics and biology of sociality in Microstigmus are restricted to just two species. Through behavioural observations and genetic analyses, we here present a detailed report on the nesting biology and social organisation of a third species, Microstigmus rosae. Our results indicate that M. rosae nests are founded by a single female and social groups appear when emerging female offspring remain on the natal nests as helpers. Adult females mass provision their offspring and developmental data are consistent with sequential brood production, an average egg laying interval of 10 days and a brood developmental period of more than 35 days. Social group formation is atypical, with 20% of nests containing up to a maximum of four adult females and two males. Adult group size is positively correlated with the number of brood in a nest, but negatively correlated with per capita brood. The sex investment ratio was female biased. Our findings support several theories concerning the behavioural characteristics thought to be important for transitions towards sociality, namely: high genetic relatedness generated by monogamous matrifilial associations, hygienic behaviour and the potential for direct reproduction. In contrast, one hypothesised trait, progressive provisioning, is notably absent, highlighting the need for investigations into the significance of post-provisioning parental care for offspring survival in this genus.