Nesting biology, phenology and sociality in a small carpenter bee Ceratina teunisseni a species endemic to Crete

Abstract Facultatively social insects are crucial for understanding the origin of sociality and the costs and benefits of social behaviour in early stages of social evolution. Ceratina bees are an excellent model taxon as this genus has a high species richness with a significant proportion of facultatively social species. In this study, we investigated the social and nesting biology of the species Ceratina teunisseni Terzo 1997. We found that C. teunisseni is a facultatively social species—both solitary and social nests occur in sympatry. The long nesting season in the Mediterranean climate allows several generations in one season. Some females of the summer generation seem to disperse and nest solitarily; however, other females remain in their natal nests as workers. The proportion of multi-female nests is the highest in September, probably because starting the nest rearing at the end of the season is more risky, while remaining in the natal nest is a safer strategy. On the other hand, social nests at the beginning of the season were never detected, therefore social nesting is associated with nest reuse during the season. The number of brood cells provisioned is generally small (4 brood cells on average). However, in social nests, the number of brood cells provisioned is usually larger than in solitary nests. Limitation by nest substrate can influence the nesting biology of this species as many nests are established by usurpation of nests of other bee or wasp species. Males are present throughout the nesting season and can sometimes be present in brood-rearing nests.