CarE1 and GST1 Are Involved in Beta-Cypermethrin Resistance in Field Populations of the Mirid Bug, Apolygus lucorum

The widespread cultivation of transgenic Bt cotton has elevated <i>Apolygus lucorum</i> (Meyer-Dür) to a major pest in cotton agroecosystems. Its rapidly developing resistance to insecticides poses a serious challenge to sustainable agriculture. In this study, we assessed the susceptibility of a field-collected population from Anyang, Henan Province, in relation to a laboratory-susceptible strain, to elucidate the present status and molecular basis of resistance to beta-cypermethrin. First, the toxicity of beta-cypermethrin to <i>A. lucorum</i> was assessed through a diet-incorporation method. Subsequently, the enzymatic activities of carboxylesterase (CarE) and glutathione S-transferase (GST) were measured, and the expression levels of <i>CarE1</i> and <i>GST1</i> were quantified by quantitative real-time PCR (qRT-PCR). Finally, the function of candidate genes was confirmed using RNA interference (RNAi) technology. The bioassays results indicated that the median lethal concentration (LC₅₀) for the laboratory and Anyang field strain were 343.34 mg/L and 700.45 mg/L, respectively. Following 48 h of exposure to the LC₃₀ of the susceptible strain, the mortality rate of the field population (20.00%) was significantly lower than that of the laboratory population (33.33%), suggesting an increase in resistance. The field population of <i>A. lucorum</i> exhibited significantly higher activities of CarE (1.61-fold) and GST (1.71-fold) compared to the laboratory strain, accompanied by 3.63- and 4.23-fold overexpression of the corresponding genes <i>CarE1</i> and <i>GST1</i>. Spatiotemporal expression profiling revealed that <i>CarE1</i> expression was highest in 4th-5th instar nymphs and adults, with predominant localization in the midgut, while <i>GST1</i> expression peaked in 4th-5th instar nymphs and was abundant in the midgut and fat body. RNAi-mediated knockdown of <i>CarE1</i> and <i>GST1</i> significantly enhanced susceptibility to beta-cypermethrin in field populations, resulting in elevated mortality 48 h post-treatment compared to controls. In conclusion, the field population of <i>A. lucorum</i> has developed considerable resistance to beta-cypermethrin, strongly correlated with overexpression of <i>CarE1</i> and <i>GST1</i>. These results deepen our understanding of metabolic resistance mechanisms and offer valuable insights for developing targeted pest control strategies.