Nest protection and foraging behaviour in solitary and social nests of the socially polymorphic orchid bee Euglossa viridissima

Natural enemies impose a selective pressure on solitary insects that may favour the evolution of sociality. In the socially polymorphic orchid bee Euglossa viridissima, females found nests solitarily and provision a first batch of brood. After brood maturity, a nest can remain solitary (all offspring disperse) or become social, when one or more subordinate daughters forage for nesting material and brood provisions for the dominant mother. Solitary females leave their nest unguarded when foraging whilst a female in a social nest can guard the nest while nestmates are foraging. By observing solitary and social nests, we found that subordinate foragers in social nests undertook longer provisioning trips than solitary females. The presence of a guarding female in a social nest protected the nest against intrusion, possibly favouring longer provisioning trips. Moreover, the frequency of successful attempts by intruders to enter nests was significantly lower in social nests. Our results provide strong support for the parasite defence hypothesis for the evolution of social behaviour.