Host size and sex allocation of parasitoids in a gall forming community.

The sex ratios of three Mesopolobus species were found to vary in different hosts in a gall-forming community in Berkshire. These relationships were consistent with Charnov's host size-sex ratio hypothesis (Charnov 1979). Due to the segregation of host species on different species of Quercus, it was possible to conduct a geographical variation experiment proposed by Charnov et al. (1981). The results of this experiment suggest that the parasitoids have a fixed 'rule of thumb' and are not flexible in their sex allocation in response to changes in host size distribution. The data, therefore, do not support the prediction of Charnov's hypothesis. Problems associated with this kind of field experiment are discussed.