SEX-ALLOCATION BEHAVIOR OF A SOLITARY ECTOPARASITOID - EFFECTS OF HOST-PATCH CHARACTERISTICS AND FEMALE DENSITY

The sex-allocation behaviour of the solitary ectoparasitoid Dinarmus b asalis (Hymenoptera: Pteromalidae) was investigated by examining the f emale's response to two proximal factors: the host-patch characteristi cs and the conspecific female density in the patch. The offspring sex- ratio of single females presented with unparasitised hosts was female biased (approximately three daughters to one son in the progeny) whate ver the host density tested. The sex-ratio in the presence of hosts pa rasitised by a conspecific 48 h beforehand was male biased. The propor tion of male offspring also increased when the number of conspecific f emales exploiting the patch changed from a single female to a group of females, whatever the group size. No sexual differences in mortality as a result of larval competition on superparasitised hosts were obser ved. The offspring sex-ratios observed in response to the host-patch c haracteristics were the result of manipulation of the egg fertilisatio n by the females during the oviposition phase. Thus, the variability o f the sex-ratio in response to an increase in the number of conspecifi c females in the same patch represented a reduction in egg fertilisati on. These results are analysed with regard to the predictions of Local Mate Competition theory and the females' host discrimination ability.