Resistance risk assessment and fitness cost of cyproflanilide in the common cutworm, Spodoptera litura (Lepidoptera: Noctuidae)

As a major crop pest, common cutworm (CCW) Spodoptera litura (Fabricius) has evolved resistance to several insecticides. Cyproflanilide is a novel meta-diamide insecticide targeting the γ-aminobutyric acid receptor (GABAR), and displays excellent insecticidal activity against lepidopteran pests, including CCW. Therefore, the resistance risk of CCW against cyproflanilide was assessed and the fitness cost was evaluated as well. After exposure with cyproflanilide for 10 generations (F10), the LC50 values of CCW against cyproflanilide increased 1.26 - fold. When the realized heritability (h2) to cyproflanilide in the field was assumed to be the laboratory-estimated value (h2 = 0.09) and the mortality of CCW was 50–90 %, 126–57 generations were required to obtain a 10-fold resistance against cyproflanilide. After selected with cyproflanilide for 10 generations, the egg duration, larval duration, pre-pupal duration and female pupal weight were significantly increased, but the pupal duration, pupation rate and life-cycle rate were significantly decreased. The mean generation time (T) of F10 was significantly prolonged by 4.39 days. The value of relative fitness (Rf) in F10 was 0.99. Although resistance developed slowly, the prolonged egg and larval durations have implications for managing CCW in the field. This information will contribute to identifying practices to delay the resistance development of CCW to cyproflanilide.