Dissecting the manipulation of lufenuron on chitin metabolism, and the sublethal effects on Helicoverpa armigera development

Abstract

Abstract Lufenuron, acting as a chitin synthesis inhibitor of benzoylureas class, is effective against many insect pests, particularly detrimental to their immature stages. However, the insecticidal activity of lufenuron has not been completely elucidated, nor do its disturbing effect on chitin metabolism genes. In this study, our bioassay demonstrated an outstanding toxicity of lufenuron against Helicoverpa armigera larvae. The treated larvae died from abortive molting and metamorphosis defects, and severe separation of epidermis and subcutaneous tissues was observed. Treatment of 3rd- and 4th-instar larvae with LC25 lufenuron significantly extended the duration of larval and pupal stage, reduced the rates of pupation and emergence, and adversely affected pupal weight. Besides, lufenuron can severely reduce chitin content in larval integument in a concentration-dependent manner, and the lufenuron-treated larvae showed reduced trehalose content in their hemolymph. Further analysis using RNA sequencing revealed that 7 of 10 chitin synthesis genes were down-regulated, whereas the expressions of two chitin degradation genes were significantly enhanced. Knockdown of chitin synthase 1 (HaCHS1), uridine diphosphate-N-acetylglucosamine-pyrophosphorylase (HaUAP), phosphoacetyl glucosamine mutase (HaPGM), and glucosamine 6-phosphate N-acetyl-transferase (HaGNPAT) in H. armigera led to significant increases in larval susceptibilities to LC25 lufenuron by 75.48%, 65.0%, 68.42% and 28.0%, respectively. Our findings therefore revealed the adverse effects of sublethal doses of lufenuron on the development of H. armigera larvae, elucidated the perturbations on chitin metabolism, and highlighted the combined administration of insect growth regulators (IRGs) and the RNAi of specific genes would be developed as a promising strategy to efficiently manage insect pests.