Parasitism of the Light Brown Apple Moth, Epiphyas Postvittana (Walker), by Its Larval Ectoparasite, Goniozus Jacintae Farrugia (Hymenoptera: Bethylidae), in Natural Populations in Victoria.

Abstract

Host-parasitoid relationships of Epiphyas postvittana (Tortricidae) and its larval ectoparasite, Goniozus jacintae were studied for 16 generations in an apple orchard and for 10 generations in a pear orchard between 1971 and 1977. G. jacintae is arrhenotokous and parthenogenetic, with unmated females producing males. It is a multiple parasitoid laying from one to seven eggs per host larva in the field, with a mean of 1.8. Parasitism is restricted to caterpillar instars III-VI, instar IV being predominantly parasitized. The life cycles of the host and the parasitoid are well synchronized, the former having three generations a year. Parasitized host larvae are found during most months of the year; numbers are maximum from October to March, when the host larvae are also in peak numbers. E. postvittana is polyphagous, occurring both on fruit trees and on dicotyledenous weed hosts in the undergrowth. G. jacintae was found in both these situations and its occurrence was related to the presence of the host larvae rather than to any association with flora or microclimate. In general, the degree of parasitism of host generations ranged from 0 to 8.3%. The impact of G. jacintae as a mortality factor of E. postvittana was insignificant. The host-parasitoid relationship was of the delayed density-dependent type.