Baseline establishment, susceptibility monitoring and risk assessment of cyproflanilide, a novel meta-diamide insecticide, against Chilo suppressalis (Lepidoptera: Crambidae) in China

The rice stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is one of the most serious pests in rice-growing areas, and it has developed resistance to most insecticides currently used in the field. Cyproflanilide is a novel meta-diamide insecticide that has shown high activities to multiple pests. Evaluating the risk of resistance to cyproflanilide in C. suppressalis is necessary for its preventive resistance management. Here we established the baseline susceptibility of C. suppressalis to cyproflanilide by the rice-seedling dipping method and topical application, and the LC₅₀ and LD₅₀ values were 0.026 mg L^–1 and 0.122 ng/larva, respectively. The LC₅₀ values of cyproflanilide in 37 field populations ranged from 0.012 to 0.061 mg L^–1, and 25 field populations exhibited resistance to chlorantraniliprole with the highest LC₅₀ value of 3,770.059 mg L^–1. In addition, a logistic distribution model analysis indicated that only 0.048 mg L^–1 of cyproflanilide was required to kill 90% field chlorantraniliprole-resistant populations of C. suppressalis, compared to 2,087.764 mg L^–1 of chlorantraniliprole for a similar level of control. Resistance screening over 19 generations did not result in resistance to cyproflanilide (RR=3.1-fold). The realized heritability (h²) of resistance was estimated as 0.067 by using threshold trait analysis, suggesting a low risk of cyproflanilide resistance development in susceptible strains. The Cypro-SEL population (F₁₀) had no obvious fitness cost (relative fitness=0.96), and no significant changes in sensitivity to seven tested insecticides. These findings suggested that cyproflanilide is a promising insecticide for the management of chlorantraniliprole-resistant C. suppressalis. Moreover, this integrated risk assessment provides scientific application guidelines for the sustainable resistance management of cyproflanilide for controlling C. suppressalis.