NUTRITIONAL ECOLOGY OF THE INTERACTION BETWEEN LARVAE OF THE GREGARIOUS ECTOPARASITOID, MUSCIDIFURAX-RAPTORELLUS (HYMENOPTERA, PTEROMALIDAE), AND THEIR PUPAL HOST, MUSCA-DOMESTICA (DIPTERA, MUSCIDAE)

In this study we examined the relationship between clutch size and par asitoid development of Muscidifurax raptorellus (Hymenoptera: Pteromal idae), a gregarious idiobiont attacking pupae of the housefly, Musca d omestica (Diptera: Muscidae). Host quality was controlled in the exper iments by presenting female parasitoids with hosts of similar size and age. This is the first study to monitor the development of a gregario us idiobiont parasitoid throughout the course of parasitism. Most fema le wasps laid clutches of one to four eggs per host, although some hos ts contained eight or more parasitoid larvae. In both sexes, parasitoi ds completed development more rapidly, but emerging adult wasp size de creased as parasitoid load increased, Furthermore, the size variabilit y of eclosing parasitoid siblings of the same sex increased with clutc h size. Irrespective of clutch size, parasitoids began feeding and gro wing rapidly soon after eclosion from the egg and this continued until pupation. However, parasitoids in hosts containing five or more paras itoid larvae pupated one day earlier than hosts containing one to four larvae. The results are discussed in relation to adaptive patterns of host utilization by gregarious idiobiont and koinobiont parasitoids.