Host Pre-Adaptation and Sublethal Indoxacarb Interactively Affect Growth and Development of Cnaphalocrocis medinalis, with Potential Involvement of P450 and Juvenile Hormone-Related Genes

Abstract

Host switching alters insecticide responses, but its interplay with sublethal stress remains unclear. We examined if host pre-adaptation modulates sublethal indoxacarb effects on Cnaphalocrocis medinalis and whether P450 and juvenile hormone-related genes are involved. Two long-term laboratory populations with different origins and rearing histories were used: a wheat-reared population (collected 2019 in Nanjing; >20 generations) and a rice-reared population (collected 2021 in Hangzhou; >10 generations). They were reciprocally transferred onto rice and wheat, establishing four host switching treatments (RR, RW, WR, WW). Second-instar larvae were exposed to LC25 indoxacarb, after which we recorded larval and pupal development, fecundity and egg hatchability, and quantified six P450 genes (CmedCYP49A1, CmedCYP6AE30, CmedCYP12A2, CmedCYP301A1, CmedCYP4V2, and CmedCYP4AE76) and four JH-related genes (CmedAT, CmedJHAMT, CmedJHE, and CmedJHBP1). Host switching was associated with altered susceptibility, with RR more susceptible than RW and WW less susceptible than WR. Developmental effects were instar-specific. Pupal traits were affected by insecticide treatment and population origin, whereas reproductive traits were mainly affected by population origin. P450 and JH-related genes showed gene-specific expression patterns and were associated with some phenotypic changes. Gene expression correlated with phenotypes, suggesting potential trade-offs among detoxification, development, and reproduction. These laboratory findings indicate that host pre-adaptation and sublethal indoxacarb affect life-history traits in trait- and instar-specific ways. P450 and JH genes are potentially involved and merit functional validation, but field validation is needed before management application.