The influence of host quality on progeny and sex allocation in the pupal ectoparasitoid,Muscidifurax raptorellus(Hymenoptera: Pteromalidae)

Abstract

AbstractMuscidifurax raptorellusKogan & Legner is a gregarious pteromalid ectoparasitoid that attacks pupae and pharate adults from several families of the higher Diptera. Egg-to-adult development time, adult parasitoid size and emerging offspring ( = secondary) sex ratio ofM. raptorelluswere compared with clutch size in two hosts that differed greatly in mass, the smallMusca domesticaLinnaeus and the largerCalliphora vomitoriaLinnaeus. The mean number of emerging parasitoids did not vary significantly with host species, although slightly higher clutch sizes were recorded inC. vomitoria. Irrespective of offspring sex, parasitoids completed development more rapidly inM. domesticathan inC. vomitoria. In the small host, the development time and adult size ofM. raptorelluswere negatively correlated with clutch size. By contrast, female parasitoid size was unaffected by clutch size in the larger host,C. vomitoria. In both hosts, female parasitoids were significantly larger than male parasitoids. The secondary sex ratio (percentage males) of emerging parasitoids was significantly lower inC. vomitoria, and varied with clutch size in both hosts. InC. vomitoria, the greatest proportion of females emerged from hosts with the highest clutch sizes, whereas inM. domesticahosts with the highest clutch sizes produced the lowest proportion of female progeny. The results described here show that the development ofM. raptorellusis profoundly affected by interspecific differences in host quality. Our results suggest that mating structure and host quality have potentially different effects on sex ratio decisions inM. raptorellus, and perhaps other gregarious parasitoids.