Thiamethoxam resistance evolution, fitness cost, and transcriptome-based functional insights in the whitefly Bemisia...

The evolution of insecticide resistance in Bemisia tabaci poses a serious threat to the sustainable control of this globally important pest. In this study, a thiamethoxam-resistant strain (TMX-G15) was established through 15 consecutive generations of laboratory selection, resulting in a 32.46-fold increase in LC₅₀ compared with the susceptible strain (TMX-G0). Realized heritability analysis indicated that thiamethoxam resistance can evolve rapidly under continuous selection pressure, particularly at higher mortality levels. Comparative life-history and age-stage, two-sex life table analyses revealed pronounced fitness costs associated with resistance, including prolonged preadult development, reduced adult longevity, shortened oviposition period, and decreased fecundity, leading to significantly lower intrinsic and net reproductive rates in TMX-G15. Cross-resistance assays showed that the resistant strain exhibited moderate to high resistance to several neonicotinoids, especially clothianidin, but remained largely susceptible to non‑neonicotinoid insecticides. Transcriptome profiling identified 2450 differentially expressed genes between TMX-G15 and TMX-G0, with enrichment in detoxification- and metabolism-related pathways. qRT-PCR validation confirmed the significant overexpression of multiple detoxification genes, including cytochrome P450s, glutathione S-transferase, and UDP-glycosyltransferases. RNA interference further demonstrated that knockdown of CYP4G15, the most strongly induced detoxification gene, significantly increased susceptibility of TMX-G15 adults to thiamethoxam and clothianidin, while no resistance-associated mutations were detected in nicotinic acetylcholine receptor subunits. Collectively, these results indicate that thiamethoxam resistance in B. tabaci is primarily mediated by enhanced metabolic detoxification and is accompanied by substantial fitness costs, providing important implications for resistance monitoring and the design of insecticide rotation strategies to delay resistance evolution.