OBSERVATIONS ON INTRASPECIFIC LARVAL COMPETITION IN THREE HYMENOPTEROUS PARASITES OF FLY PUPARIA

Abstract

Though they may hatch on any part of a housefly (Musca domesticaL.) pupa, most larvae ofNasonia vitripennis(Walk.) andMuscidifurax raptorG. & S. (Hymenoptera: Pteromalidae) move to the host’s ventral abdominal area, and those ofSpalangia cameroniPerk. (Hymenoptera: Pteromalidae) to the dorsal side of the abdomen, before feeding extensively. As many as 25 larvae ofN.vitripenniscan mature on a medium-sized housefly pupa; if more are present initially, those that hatch last usually die from starvation after the host has been consumed. In contrast, usually only one larva ofM.raptororS.cameronimatures on a host; this is often the larva that hatches first, because it attacks all parasite eggs that it encounters while moving over the fly pupa soon after hatching. Larval crowding inM.raptororS.cameroni, unlike that inN.vitripennis, does not affect the sex ratio of the survivors.