Selective toxicity of twelve insecticides to Spodoptera frugiperda and Tetrastichus howardi (Olliff).
Objective: To provide the scientific evidence for the coordination of the chemical and biological control of Spodoptera frugiperda, this paper evaluated the toxicity and selectivity of twelve insecticides to S. frugiperda and its natural enemy Tetrastichus howardi. Method: The corn leaf dipping method and residual film method were used to evaluate the selective toxicity of the 12 insecticides including 40% bisultap, 94% cyantraniliprole, 98% thiamethoxam, 94% indoxacarb, and Metarhizium anisopliae to the second instar larvae of S. Frugiperda and the adults T. howardi, to clarify the sensitivity of S. frugiperda and T. howarditothe commonly used insecticides. Result: Among the 11 chemical insecticides, 95% emamectin benzoate had the highest toxicity to the second larvae of S. frugiperda and the median lethal concentration(LC50)50 for 24 hours was 0.42 mg/L. While 98% thiamethoxam had the lowest toxicity(24 h-LC50 was 13.56 mg/L). 95% emamectin benzoate also had the highest toxicity to the adult T. howardi(24 h-LC50 was 0.09 mg/L). 94% indoxa carb had the lowest toxicity(24 h-LC50 was 4.45 mg/L). The order of the selective toxicity ratio(STR)of the 11 chemical insecticides was as follow: 94% indoxacarb>96% flubendiamide>95% chlorfenapyr>95.3% chlorantraniliprole>95% emamectin benzoate>98% lufenuron≈98% thiamethoxam>94% cyantraniliprole>81.2% spinetoram≈40% bisultap>95% tetrachlorantraniliprole. This order suggested 94% indoxacarb had the strongest protective effect on T. howardi on the premise of controlling S. frugiperda. The LC50 and STR of metarhizium anisopliae against S. frugiperda and T. howardi presented the tendency of decrease with time passing by, reaching the maximum on the 4th day, and the minimum on the 6th day, which suggested that there was a lag process before the biological insecticides displayed their efficacy. Conclusion: 95% emamectin benzoate has the highest toxicity, and thus it can be the first choice to emergently control S. frugiperda;M. anisopliae and 94% indoxacarb have the highest selectivity, and thus can be recommended as the drug which can comprehensively control S. frugiperda;94% cyantraniliprole and 98% thiamethoxam have the lowest toxicity, and therefore they are not fit for the chemical control of S. frugiperda.