Lethal and sublethal effects of Chrysodeixis includens nucleopolyhedrovirus (ChinNPV)-based biopesticide infecting different larval ages of soybean looper

Abstract

ABSTRACT Laboratory studies that evaluated lethal and sublethal effects of a commercial biopesticide containing Chrysodeixis includens nucleopolyhedrovirus (ChinNPV: Baculoviridae: Alphabaculovirus) infecting different larval ages of soybean looper (SBL), Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) are presented. Larvae were infected with different concentrations of ChinNPV by droplet feeding (neonates) and diet surface spray bioassays (neonates and third instar). The following biological parameters were evaluated: larval survival at 7- and 14-d post-infection and at moth eclosion; duration of larval, pupal and larval-to-adult periods; larval and pupal weights; sex ratio; moth deformities; fecundity and fertility. A fertility life table was also developed. Results indicated that neonates of SBL did not develop into adults at the highest concentrations of ChinNPV in both bioassays methods. In contrast, a proportion of the exposed larvae survived to adulthood when exposed to the lowest concentrations (neonates) and in all concentrations tested (third instar). SBL neonates surviving exposure to estimated LC50 and LC75 concentrations (droplet feeding bioassays) had low larval weight, reduced fecundity and fertility, altered sex ratio, and produced fewer females per female. Surviving third instar SBL exposed to the highest concentrations showed low weight and sex ratio alterations. Our findings indicated that, beyond lethal effects, the commercially available baculovirus-based insecticide containing ChinNPV also had substantial sublethal effects on neonates and third instar SBL. In field conditions, these sublethal effects can potentially cause a significant impact in the local population dynamics, including reduction in numbers and infestation levels.