Oviposition strategy of the parasitic waspDinarmus basalis (Hymenoptera,Pteromalidae)

Summary Host type choice and sex allocation were examined using the solitary parasitic waspDinarmus basalis (Pteromalidae, Hymenoptera) parasitizing larvae or pupae of the bean weevilCallosobruchus chinensis (Bruchidae, Coleoptera) within azuki beans (Vigna angularis). The wasps were offered two types of host; one was hard for the mother to lay eggs in, but was more beneficial for the offspring; the other was easy for the mother to lay eggs in, but was less beneficial for the offspring. The two types of host were one large host (17-day old host) in one bean and 6 small hosts (12-, or 13-day old hosts) in one bean. The same number of each host was presented at the same time to female wasps. The wasps accepted more 17-day old hosts than 12-day old hosts, and more 13-day old hosts than 17-day old hosts in each pair-wise choice experiment. The proportions of accepted host types were different from the proportions predicted by optimization models of random prey encounter with known or unknown prey densities. The wasps showed partial preference of host types. Incomplete information about prey densities, and about the costs and benefits of the two types of host may have generated the partial preference. Two predictions of host sizemodels, that (1) there should be a negative relationship between host size and offspring sex ratio (proportion of male offsprings), and (2) the sex ratio in each size host changes with the relative frequency of each size host utilized, were qualitatively supported.