Sex‐allocation behaviour of a solitary ectoparasitoid: effects of host‐patch characteristics and female density

Abstract

AbstractThe sex‐allocation behaviour of the solitary ectoparasitoid Dinarmus basalis (Hymenoptera: Pteromalidae) was investigated by examining the female's response to two proximal factors: the host‐patch characteristics 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) whatever the host density tested. The sex‐ratio in the presence of hosts parasitised by a conspecific 48 h beforehand was male biased. The proportion of male offspring also increased when the number of conspecific females 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 observed. The offspring sex‐ratios observed in response to the host‐patch characteristics were the result of manipulation of the egg fertilisation by the females during the oviposition phase. Thus, the variability of the sex‐ratio in response to an increase in the number of conspecific females in the same patch represented a reduction in egg fertilisation. These results are analysed with regard to the predictions of Local Mate Competition theory and the females' host discrimination ability.