Combination of diflubenzuron and RNAi technology to improve the control effect of Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera, stands as a major agricultural pest, displaying resistance to a diverse range of insecticides. Diflubenzuron, a member of the benzoylurea class of insecticides, serve by suppressing the synthesis of chitin in insects. This disruption hampers their typical metamorphic processes like molting and pupation, ultimately culminating in death. In this study, the toxicity of diflubenzuron against H. armigera was investigated. The results showed that the LC50 of diflubenzuron on 3rd instar bollworm was 109 mg/kg after 7-day exposure. Most importantly, diflubenzuron treatment led to a change in the chitin synthesis pathway, accompanied by a significant surge in chitinase (HaChi) expression. The feasibility of combining with RNA interference (RNAi) technology to control cotton bollworm was further explored. We demonstrated that three chitin synthesis pathway genes Chitin synthase 1 (HaCHS1), chitin synthase 2 (HaCHS2) and HaChi were significantly inhibited following exposure to dsRNAs, leading to the death of cotton bollworm. Among these, the dsHaCHi treatment group manifested the most significant effect. Subsequent combined treatment of 3rd instar larvae with dsHaChi and diflubenzuron reduced survival rates of cotton bollworm by 24% and 15.33%, respectively. Simultaneously, there were recognized effects on larval weight, pupal weight, and pupation rate to varying degrees. This study underscores the potential of combining RNAi technology with conventional chemical pesticides, this combination can improve pest control efficiency, and offers a novel strategy to compensate for the low RNAi efficiency in lepidopteran insects, consequently reducing the dependency on chemical pesticides.