Intraspecific Parasitism and Nesting Success in the Solitary Wasp Ammophila Sabulosa

Abstract

The nesting behaviour of marked female solitary wasps, Ammophila sabulosa (L.) (Sphecidae), was studied over two seasons at a Norfolk heathland site. Females mass provisioned unicellular nests with 1-5 paralysed caterpillars. Intraspecific parasitism was the major mortality factor before the egg hatched - approximately 28% of eggs were destroyed by parasites. Parasites stole caterpillars to provision their own nests, replaced host eggs with their own eggs (brood parasitism), or simply discarded prey from host nests. Hosts were ineffective at preventing parasitism. Individual females both provisioned their own nests and parasitized those of other females. Parasitism usually occurred soon after the previous activity at the host nest. Parasitism events were clumped at certain nests, which were parasitized up to five times each. Once a nest had been brood parasitized, the prey were significantly more likely to be stolen or discarded than were prey in unparasitized nests, and only 17 % of eggs laid by brood parasites survived. Circumstantial evidence suggests that chemical stimuli are important in detection of host nests by parasites. High levels of intraspecific parasitism have rarely been reported in solitary wasps and bees, and parasitic behaviour is rare and unspecialized in some other Ammophila species. Parasitism by miltogrammine flies was of relatively minor importance in A. sabulosa as in other Ammophila species, probably because provisioning events, during which flies larviposit, are few and well separated in time.