Some Effects of Host Age on Parasitism byNasonia vitripennis(Walk.) (Hymenoptera: Pteromalidae)

Abstract

AbstractMortality of immatureNasonia vitripennis(Walk.) was least on young house fly pupae (less than 48 hours old, at 24.5 ± 0.5 °C.) and increased with increasing host age. Increased mortality on old hosts was manifested principally as a decrease in female adult progeny, numbers of adult males and of mature diapause larvae remaining approximately constant. Reduction in the percentage of females in the adult progeny reared on old hosts probably resulted from superparasitism. This kills more female than male larvae and occurred more commonly on old hosts, each of which provides a smaller quantity of suitable food for the immature parasites. Adults reared on old hosts were smaller and relatively fewer of them were able to emerge. The proportion of the total mature parasite progeny that remained in diapause was greater on old hosts, probably because of qualitative differences in the food provided by hosts of different ages.