INTRANIDAL MATING, EMERGENCE, AND SEX-RATIO IN A COMMUNAL BEE ANDRENA-JACOBI PERKINS-1921 (HYMENOPTERA, ANDRENIDAE)

The extent of preemergence intranidal mating, schedules of emergence, and sex ratio at emergence were documented for Andrena jacobi, a commu nal, univoltine bee, by collecting and dissecting adults as they emerg ed from their fossorial nests in 1994. Over 70% of females had mated i ntranidally with nestmate males, thus potentially incestuously, before emerging. Preemergence intranidal mating did not vary during a day or between nests within a day, though it was less frequent at the start and end of the period of emergence. It was independent of a female's s ize. A. jacobi was protandrous, though some males emerged after all fe males. The sex ratio at emergence was remarkably female biased, possib ly a consequence of local mate competition. Intranidal mating may repr esent a characteristic trait of communal bees where a high density of receptive females are predictably aggregated within a nest.