Biochemical mechanism of emamectin benzoate resistance in citrus mealybug, Planococcus citri (Hemiptera: Pseudococcidae); cross-resistance and realized heritability

Chemical control is the most common method used to suppress pest populations in crops and orchards, but this practice often leads to the development of resistance and eventual control failure. The citrus mealybug, Planococcus citri (Homoptera: Pseudococcidae), is a major pest in citrus orchards worldwide. Resistance development in P. citri not only causes significant economic losses for citrus growers but also contributes to environmental pollution and food safety concerns. Effective pest management programs are essential to minimize environmental pollution and protect human health. A study was conducted to assess the current levels of resistance to emamectin benzoate in P. citri, explore the resistance mechanisms, estimate the realized heritability (h(2)), and evaluate cross-resistance to acetamiprid, spinosad, and fipronil. After four generations of selection, moderate resistance to emamectin benzoate was observed in P. citri (27.98-fold) compared to the unselected (UNSEL) population. However, this resistance did not affect susceptibility to spinosad, fipronil, or acetamiprid. The estimated realized heritability of resistance to emamectin benzoate was 0.65, indicating a substantial potential for resistance to increase under continued selection pressure. The study also found that resistance was synergized by PBO or DEF, suggesting a possible link to mono-oxygenases or esterases. The absence of cross-resistance to other insecticides, such as spinosad, fipronil, and acetamiprid, supports the rotational use of these chemicals. However, the high heritability value points to increased additive genetic variance, which could lead to a rapid increase in resistance. Therefore, while rotating emamectin benzoate with other insecticides could help manage P. citri in the field, further studies on resistance management strategies are essential.