Impact of Helicoverpa armigera nucleopolyhedroviruses expressing a cathepsin L-like protease on target and nontarget insect species on cotton

Baculoviruses have been genetically engineered to improve their insecticidal properties and reduce crop damage. In this study, a recombinant Helicoverpa armigera nucleopolyhedrovirus (HearNPV-cathL) expressing a cathepsin L-like cysteine protease from the flesh fly, Sarcophaga peregrina, was constructed. Its insecticidal properties in the laboratory, occlusion body yield in diseased larvae, efficacy of protecting cotton from larval feeding damage and impact on predator densities in the fields were assessed. In the laboratory, the infectivity of this recombinant was not different from the wild-type parent (HearNPV-WT) and a recombinant virus (HearNPV-AaIT) which expresses an insect-selective neurotoxin from the scorpion Androctonus australis. The median survival times of 2nd or 3rd instar H. armigera larvae after infection with HearNPV-cathL were reduced about 26% in comparison to HearNPV-WT. Occlusion body yield in the diseased larvae inoculated with HearNPV-cathL, which were similar to that with HearNPV-AaIT, was reduced 63% in comparison to HearNPV-WT. In the field, when virus formulations were multiply applied to control natural infestations of H. armigera on cotton, both HearNPV-cathL and HearNPV-AaIT treatments protected cotton from larval feeding damage better than the wild-type virus treatment. Predator densities in the recombinant virus treatments were similar to those in wild-type virus treatments and untreated control. These results suggest that the recombinant HearNPVs have potential for practical use.