Mating in a communal bee, Andrena agilissima (Hymenoptera Andrenidae)

Males of the fossorial, communal bee Andrena agilissima (Scopoli 1770) typi cally search for mates at flowers from which females collect pollen (WESTRI CH 1989). To investigate whether communal nesting also affords mating oppor tunities for adults freshly eclosed from brood cells, we collected and diss ected females that were emerging for the first time in spring from their na tal nests and examined the contents of their spermathecae. Circa 97% of fem ales contained spermatozoa in their spermathecae, indicating a high Frequen cy of preemergence intranidal mating. Bees also copulated above ground, bot h near nest entrances and at flowers. In the latter situation, pollen-colle cting females were seen to copulate, suggesting that A. agilissima females mate repeatedly (polyandry) and are sexually receptive across adulthood. Th e schedules of emergence of males and females from natal nest entrances in spring overlapped to a large extent; the species was neither markedly prota ndrous nor protogynous on the island of Elba, Italy, in 1998. These emergen ce patterns are consistent with both pre-emergence intranidal mating and po lyandry linked to female receptivity extended across adulthood. The sex rat io at emergence was female biased (numerical proportion of males, MIM + F = 0.38), consistent with the view that pre-emergence intranidal mating gener ates local mate competition amongst males, and that it is an important comp onent of the mating biology of A. agilissima. The mating opportunities of s ons within the nest may potentially provide a selective benefit to communal nesting by females.