Host age preference and sex allocation in the pupal parasitoid Itoplectis naranyae (Hymenoptera: Ichneumonidae)

To understand the reproductive biology of Itoplectis naranyae Ashmead, a major pupal parasitoid of lepidopteran pests in the paddy field, the acceptability and suitability of hosts of different ages and the resultant allocation of sexes in these hosts were studied. Prepupae and 0- to 11-d-old pupae of Galleria mellonella (L.) were used as hosts. Although female wasps attacked all host age classes almost equally, they frequently rejected 8- to 11 -d-old host pupae after drilling into them. Host pupae 8-11 d old also were less suitable for larval development than prepupae and pupae 0-7 d old. Thus, females preferentially oviposit on hosts suitable for larval development The sex ratio of the offspring that emerged from host pupae 8-11 d old were more male-biased than those from prepupae and pupae 0-7 d old The male-biased sex ratio in pupae S-11 d old was caused by sex allocation adjustment by females rather than by differential larval mortality between the sexes. Host selection and sex allocation by pupal parasitoids are discussed in the context of simple optimal diet theories and sex ratio theories.