Down‐regulation of the <scp> <i>PxJHE2</i> </scp> gene elevates juvenile hormone titers and compensates for fitness costs of Bt <scp>Cry1Ac</scp> resistance in <scp> <i>Plutella xylostella</i> </scp> (L.)

BACKGROUND: Unraveling the compensatory mechanisms that mitigate fitness costs associated with resistance to Bacillus thuringiensis (Bt) pesticidal proteins is essential for delaying the evolution of Bt resistance. The diamondback moth Plutella xylostella, the first insect reported to evolve field resistance to Bt biopesticides, serves as an ideal model for elucidating the compensatory mechanisms underlying Bt resistance, as its evolution of Bt Cry1Ac resistance is not always accompanied by significant fitness costs. In this study, we identified a novel juvenile hormone esterase (JHE) gene (PxJHE2) and explored its role in compensating for the fitness costs associated with Bt Cry1Ac resistance in P. xylostella. RESULTS: We found a noncanonical JHE gene through sequence alignment and phylogenetic analysis. Metabolic analysis based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) demonstrated that PxJHE2 possesses the ability to degrade juvenile hormone (JH) into JH acid. We cloned PxJHE2 gene, and found its expression was significantly reduced in the midgut of both Bt Cry1Ac-treated and Bt-resistant strains. Furthermore, small interfering RNA (siRNA)-mediated silencing of PxJHE2 gene significantly increased JH titers, accompanied by significant fitness costs such as reduced fecundity, decreased pupation rate, and lowered eclosion rate. CONCLUSION: Our findings identify PxJHE2 as a key regulator of JH homeostasis that mediates compensation of fitness costs in Bt Cry1Ac-resistant P. xylostella. Targeting PxJHE2 or its hormonal regulatory pathway may provide a promising strategy to disrupt resistance-associated compensatory mechanisms, thereby enhancing the sustainability of Bt-based pest management programs. These results further provide valuable molecular insights for the development of innovative bioinsecticide strategies. © 2026 Society of Chemical Industry.