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, th e acceptability and suitability of hosts of different ages and the res ultant allocation of sexes in these hosts were studied. Prepupae and 0 - to 11-d-old pupae of Galleria mellonella (L.) were used as hosts. Al though female wasps attacked all host age classes almost equally, they frequently rejected 8- to 11-d-old host pupae after drilling into the m. Host pupae 8-11 d old also were less suitable for larval developmen t than prepupae and pupae 0-7 d old. Thus, females preferentially ovip osit on hosts suitable for larval development. The sex ratio of the of fspring 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 rati o in pupae 8-11 d old was caused by sex allocation adjustment by femal es rather than by differential larval mortality between the sexes. Hos t selection and sex allocation by pupal parasitoids are discussed in t he context of simple optimal diet theories and sex ratio theories.