Discrete and Interactive Effects of Plant Resistance and Nuclear Polyhedrosis Viruses for Suppression of Soybean Looper and Velvetbean Caterpillar (Lepidoptera: Noctuidae) on Soybean

Abstract

Laboratory and fieid tests with two nuclear polyhedrosis viruses (NPV) infective to the soybean looper (SBL), Pseudoplusia includens (Walker), and velvetbean caterpillar (VBC), Anticarsia gemmatalis Hübner, were conducted to investigate the effects of their integration with resistant host plants for suppression of SBL and VBC on soybean, Glycine max (L.) Merrill. The soybean genotypes were an insect resistant soybean breeding line GatIR 81-296 and a susceptible cultivar (‘GaSoy 17’). In the laboratory study, foliage consumption of late-ins tar SBL reared on the resistant genotype was severely inhibited, but VBC foliage consumption was not different on the two genotypes. NPV-infected larvae of both species consumed significantly less foliage when reared on the resistant genotype than on the susceptible genotype. Although total numbers of SBL and VBC larvae generally were not significantly lower in field plots of the resistant genotype, numbers of medium-sized VBC and large SBL larvae were significantly reduced on the resistant genotype during times of peak population density. An application of VBC NPV reduced total numbers of VBC larvae by 76% (‘GaSoy 17’ plots) and 72% (81-296 plots) at 7 d after application. SBL NPV appeared to work more slowly against host larvae; however, total numbers of SBL larvae were suppressed by 78% (‘GaSoy 17’ plots) and 76% (81-296 plots) by 14 d after application. Both pathogens were effective in reducing numbers of host larvae and percentage of defoliation in plots of resistant or susceptible soybean.