Movement of Nuclear Polyhedrosis Virus into Velvetbean Caterpillar (Lepidoptera: Noctuidae) Larval Populations on Soybean by Nabis roseipennis (Heteroptera: Nabidae) Nymphs

Abstract

Nabis roseipennis Reuter nymphs that preyed on larvae of the nuclear polyhedrosis virus (NPV) infected velvetbean caterpillar, Anticarsia gemmatalis (Hübner), excreted the virus (AgNPV) for several days thereafter. Based on bioassays, fifth instar and second instar nymphs excreted 84.7 × 105 and 9.7 × 105 polyhedral inclusion bodies (PIB) per nymph, respectively. The AgNPV-contaminated nymphs effectively disseminated the virus via the feces over soybean plants where it served as inoculum to initiate disease in larval populations of A. gemmatalis caged in the field. Larval mortality from AgNPV ranged from 11.4 to 48.5% over treatments in two tests. Larval mortality in treatments where the source of virus inoculum was AgNPV-contaminated fifth instar nymphs was similar to that in treatments where the source of viral inoculum was diseased larvae. Larval mortality resulting from AgNPV dissemination by the nymphs was usually higher in treatments containing fifth instar nymphs than in those with second instar nymphs. Dissemination of NPV by fifth instar nymphs was higher in mixed-age than in uniformed-age A. gemmatalis larval populations. This was not the case with the smaller second instar nymphs.