CHALCID PARASITOID ATTACK ON A GALL WASP POPULATION (ACRASPIS HIRTA (HYMENOPTERA: CYNIPIDAE)) ON QUERCUS PRINUS (FAGACEAE)

Abstract

The developmental sequence of the asexual generation of the gall wasp Acraspis hirta Bassett (Hymenoptera: Cynipidae) on its host plant Quercus prinus (Fagaceae) is described from a site in New Jersey. Chalcid attack was the key mortality factor in the gall population. Parasitoids concentrated their attack on host galls before galls matured and hardened. Hardening of gall walls appears to be the most important deterrent to later attack by inhibiting oviposition. Parasitoids which emerged from A. hirta galls did not reinfest the surviving hosts but probably shifted to other gall species. The parasitoids of Cynips divisa, a similar Old World gall species, became progressively more generalized in their feeding preferences as the season progressed. No such temporal sequencing wau observed in A. hirta.Spacing out of A. hirta galls among leaves is an important strategy for increasing individual fitness in response to parasitoid attack. Most trees were sparsely infested, and few leaves supported more than one gall. Parasitoid mortality was significantly higher on multiply infected leaves than on leaves with one gall. Galls which were parasitized had a significantly smaller average distance to the nearest neighboring gall than those that escaped parasitism suggesting a slight resource concentration effect.