Field inactivation of wild-type and genetically modified Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus in cotton

Cotton bollworm (Helicoverpa armigera) is a serious pest on cotton in China. A specific baculovirus, H. armigera nucleopolyhedroviruses (HaSNPV) is used as a commercial biopesticide to control this pest. To improve the pesticidal properties, HaSNPV has been genetically engineered by both deleting the ecdysteroid UDP-glucosyltransferase (egt) gene from its genome (recombinant HaSNPV-EGTD) and incorporating an insect-selective toxin gene from the scorpion Androctonus australis (AaIT) (recombinant HaSNPV-AaIT). In the field, there was no significant difference among the inactivation rates of the two recombinant HaSNPVs and their parent wild-type, HaSNPV-WT. The inactivation rate of these viruses was significantly different in different years. The average half-life of HaSNPV was 0.57, 0.90 and 0.39 days in 2000, 2001 and 2002, respectively. Inactivation rates correlated well with solar radiation over these years.