Selective and persistent toxicity of seven insecticides to five egg parasitoids of Spodoptera frugiperda

Abstract

Abstract Background Spodoptera frugiperda, a major migratory and invasive pest, inflicts significant yield loss on rice and maize in China. As part of an integrated pest management system, biological control agents can be used against S. frugiperda, especially egg parasitoids. However, limited evidence exists regarding the combined and persistent effects of various pest control products on those parasitoids. Results This study examined the selective and persistent toxicity of seven approved pesticides [chlorantraniliprole, lufenuron, emamectin benzoate, spinetoram (synthetic pesticides), Mamestra brassicae Nuclear Polyhedrosis Virus (MabrNPV), Bacillus thuringiensis (Bt) (biopesticides) and a chlorantraniliprole-lufenuron mixture (3:1) treatment] to five species of egg parasitoids, namely Trichogramma dendrolimi, Trichogramma chilonis, Trichogramma mwanzai, Trichogrammatoidea lutea, and Telenomus remus. The residual toxicity tests revealed that spinetoram showed high toxicity to T. mwanzai, T. dendrolimi, and T. chilonis in adults stage with mortality of over 92.6%, but caused low mortality in T. lutea (64.9%) and T. remus (49.2%) when used at the recommended rate. However, after treated by chlorantraniliprole, lunefuron, chl. + luf. (3:1), MabrNPV, and Bt, the mortality rates of all tested parasitoid adults were below 25% (lunefuron lower than 10%). A 3-day emamectin benzoate treatment caused 90% mortality in T. mwanzai, T. lutea, T. dendrolimi, and T. chilonis adults. The 3:1 mixture of chlorantraniliprole and lufenuron did not affect the lifespan of T. mwanzai and T. lutea. Chlorantraniliprole exhibited exceptional safety for all developmental stages (adult, egg, and pupa) of the five egg parasitoid species. A risk analysis indicated that chlorantraniliprole, MabrNPV, Bt, and the 3:1 mixture had the least toxicity to the five tested parasitoid adults, followed by lufenuron. Conversely, spinetoram and emamectin benzoate displayed moderate toxicity to adults of all tested parasitoid species. Conclusion Our findings indicate that chlorantraniliprole is safe for the five egg parasitoids species studied even after prolonged use and can be used in conjunction with lufenuron. However, spinetoram and emamectin benzoate had the potential to be harmful to these parasitoids.