Insecticide resistance and target-site mutations in field populations of Tuta absoluta in China

The tomato leafminer, Tuta absoluta, poses a severe threat to tomato production in China, yet regional resistance patterns remain poorly characterized. This study investigates the insecticide resistance status and underlying molecular mechanisms in field populations of T. absoluta across major tomato-producing regions in China. Ten populations were evaluated for susceptibility to seven commonly used insecticides using standardized bioassays, alongside screening for resistance-associated target-site mutations in key genes. The results indicate that most populations remain susceptible to spinetoram, abamectin, and indoxacarb, supporting their continued effectiveness in field control. However, moderate resistance to emamectin benzoate was detected in several populations, with resistance ratios reaching up to 75.09 fold. Additionally, low to moderate resistance to Bacillus thuringiensis (Bt) and broflanilide was observed in certain regions. Although resistance ratios to bifenthrin were relatively low, consistently high LC₅₀ values suggest a widespread reduction in baseline susceptibility. Molecular analyses revealed that the L1014F mutation in the voltage-gated sodium channel (VGSC) gene was fixed across all populations, while M918T and T929I mutations occurred at high frequencies. Notably, no significant correlation was found between these mutations and phenotypic resistance levels, and no resistance-associated mutations were detected in the nAChR gene. These findings highlight the complex and potentially multifactorial nature of resistance in Chinese T. absoluta populations and provide important guidance for optimizing insecticide rotation and resistance management strategies.