Duration of the Egg Stage of the Sexes in Pseudeucoila Bochei Weld (Cynipidae), a Parasite of Drosophila Larvae

Abstract

In an earlier study it has been demonstrated that Pseudeucoila females are able to discriminate between host larvae which have been par- asitized and hosts which have not been parasitized (BAKKER et al., 1967). However, this ability does not always prevent superparasitiza- tion. Especially in cases where the ratio of wasps to hosts is high, a large number of hosts is found with two or more eggs. JENNI (1951) claimed that from superparasitized hosts a higher proportion of female wasps emerged. He attributed this to a better chance of survival for the female parasite larvae in those host larvae in which a female and a male parasite larva were present. Differences in development between the sexes in the early stages would favour the females. JENNI did not, however, present evidence for developmental differences between the sexes. In our experiments on this subject it appeared that the relation between superparasitization and sex ratio found by JENNI is by no means always clear. This may be due to various factors, the major one being the enormous variability in the sex ratios of the offspring of different females. However that may be, the problem of possible differences in the rate of egg development between the sexes of the parasite was tackled and a method was devised to study it.