Decreased carboxylesterase expression associated with increased susceptibility to insecticide in Mythimna separata

Carboxylesterases are one of the three major types of detoxification enzyme in insects. In this study, we screened 12 full-length carboxylesterase cDNA sequences from the oriental armyworm Mythimna separata; they were named MsCarE1-MsCarE12 and registered in GenBank with accession numbers MK440541-MK440552. Treatment of fourth instar larvae of M. separata with the LD₅₀ of the insecticide chlorantraniliprole increased the expression levels of MsCarE3 and MsCarE4, while treatment with the LD₅₀ of lambda-cyhalothrin significantly increased the expression levels of MsCarE5 and MsCarE10. Spatiotemporal expression detection showed that MsCarE3, MsCarE4, MsCarE5, and MsCarE10 were expressed at different developmental stages and in different tissues of M. separata and their expression levels were different. Induction using a high dose of chlorantraniliprole resulted in lower expression of MsCarE3 and MsCarE4. LD₅₀ of lambda-cyhalothrin induced higher expression of MsCarE5 and MsCarE10, while LD₇₀ induced higher MsCarE10 expression at 3, 6, and 12 h after treatment. RNA interference successfully inhibited the expression of MsCarE3, MsCarE4, MsCarE5, and MsCarE10, to different degrees at different time points. Silencing of MsCarE5, or MsCarE5 and MsCarE10 simultaneously changed carboxylesterase activity and increased the susceptibility of M. separata larvae to lambda-cyhalothrin. This study provides a new method to increase the insect susceptibility to insecticide.