Host-age preference of Theocolax elegans (Westwood) (Hymenoptera: Pteromalidae), a larval parasitoid of the lesser grain borer, Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) and the cowpea weevil, Callosobruchus maculatus

Abstract

The pteromalids (Hymenoptera: Pteromalidae) Anisopteromalus calandrae (Howard), Dinarmus basalis (Rondani), Lariophagus distinguendus (Forster), Pteromalus cerealellae (Ashmead) and Theocolax elegans (Westwood) are solitary larval ectoparasitoids used to suppress several species of stored-product insects that infest storage grains. We investigated host-age preference of T. elegans using no-choice laboratory experiments. Lesser grain borer, Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) larvae (9, 11, 13, 15, 17, 19, 21 and 23 days-old) in wheat grain kernel and cowpea weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae) larvae (5–19 days-old) in cowpea beans were exposed to neonate T. elegans mated females to lay their eggs for two days. Our results showed that the highest number of parasitoids emerged from 23 days-old R. dominica larvae. The numbers of parasitoids emerged from 19, 21 and 23 days-old R. dominica larvae were statistically significantly different in experiments (F-test, 0.05). Progeny of T. elegans reared from R. dominica and C. maculatus larvae were either fully-winged (macropterous), short-winged (brachypterous) or wingless (apterous). Female T. elegans were rarely host-feeding on C. maculatus larvae. Theocolax elegans progeny were emerging from 14 days-old C. maculatus larvae only. We discussed insectary mass production of T. elegans for biological control.