Overwintering strategy and longevity of European small carpenter bees (Ceratina)

Abstract

Aculeate Hymenoptera have two modes of overwintering. In solitary species, adults usually do not emerge before winter and overwinter in their natal nests. In the majority of social species, adults activate before winter and only inseminated females perform overwintering. We examined the winter survival strategy in four species of small carpenter bees (Ceratina) in which both sexes activate before winter and overwinter as adults. All of the species studied are able to use their old nests, nests of other Ceratina species, or newly excavated burrows for overwintering. However, the species differ in their strategy. Ceratina cucurbitina usually overwintered in social hibernacula with a large number of individuals, but social hibernation was less often present in C. nigrolabiata. On the other hand, individuals of C. chalybea and C. cyanea overwintered predominantly solitary. Interestingly, we detected female individuals that attempted to overwinter for a second time in all species. Surprisingly, males of C. nigrolabiata and C. chalybea are also able to overwinter for a second time in rare cases. These males lived for more than 1.5 years; therefore, they are the longest living bee-males known to date.