Parasitism of Helicoverpa assulta Guenée (Lepidoptera: Noctuidae) eggs by Trichogramma spp. (Hymenoptera: Trichogrammatidae): Implications for inundative release on tobacco plants

Abstract

To screen effective Trichogramma species or strains and to characterize their parasitism against Helicoverpa assulta eggs, parasitism by T. dendrolimi and T. chilonis was compared in glass tube and cage tests, and the effects of host egg age and location, and plant species were investigated. In the glass tube test, HJS and YYS strains of T. dendrolimi, and JDM and GGM strains of T. chilonis parasitized 72.2-97.6% of host eggs. In the mesh cage test, the JDM strain parasitized the highest (60.1±24.9%) and the GGM strain, the lowest (39.4±28.6%) level of host eggs. Host egg age showed significant influence on parasitism, and HJS, YYS and JDM strains all preferred 0-12 h to 12-36 h host eggs. The wasps parasitized significantly more host eggs on lower than on upper and bottom leaves, and a higher proportion of host eggs on the leaf upper side than on the lower side regardless of plant height, which contrasted to egg deposition by H. assulta. On pepper plants, parasitism by T. dendrolimi and T. chilonis was 31.1±13.9% and 32.8±10.2%, respectively, while on tobacco plants, it was 10.6±4.6% and 1.1±0.8%, respectively. The implications of these results are discussed with reference to inundative release.