Efficacy and Residual Toxicity of Insecticides on Plutella xylostella and Their Selectivity to the Predator Solenopsis saevissima

SIMPLE SUMMARY: Insecticides that cause high mortality on pest insects while having a low impact on natural enemies are necessary for crop protection. Our study aimed to test commercial insecticide toxicity and residual activities against Plutella xylostella and the predator ant Solenopsis saevissima. Seven of the nine evaluated insecticides (bifenthrin, chlorfenapyr, chlorantraniliprole, cyantraniliprole, indoxacarb, spinetoram, and spinosad) caused mortality ≥80% of P. xylostella. In addition, four insecticides had a long-lasting effect in the field: chlorantraniliprole, cyantraniliprole, spinetoram, and spinosad. Chlorantraniliprole and cyantraniliprole always caused mortality <30% to S. saevissima. Furthermore, four days after application, spinetoram and spinosad caused lower mortality in the predator ant than the pest. Therefore, chlorantraniliprole and cyantraniliprole are highly recommended for controlling P. xylostella since they effectively control the pest with a low toxic effect on predator S. saevissima. ABSTRACT: We evaluated the efficacy and residual toxicity of nine commercial insecticides on Plutella xylostella and their selectivity to the predator ant Solenopsis saevissima under laboratory and field conditions. First, to test the insecticides’ effectiveness and selectivity, we conducted concentration-response bioassays on both species and the mortalities were recorded 48 h after exposure. Next, rapeseed plants were sprayed following label rate recommendations in the field. Finally, insecticide-treated leaves were removed from the field up to 20 days after application and both organisms were exposed to them as in the first experiment. Our concentration-response bioassay indicated that seven insecticides caused mortality ≥80% of P. xylostella: bifenthrin, chlorfenapyr, chlorantraniliprole, cyantraniliprole, indoxacarb, spinetoram, and spinosad. However, only chlorantraniliprole and cyantraniliprole caused mortality ≤30% of S. saevissima. The residual bioassay indicated that four insecticides had a long-lasting effect, causing mortality of 100% to P. xylostella 20 days after application: chlorantraniliprole, cyantraniliprole, spinetoram, and spinosad. For S. saevissima, bifenthrin caused mortality of 100% during the evaluated period. Additionally, mortality rates below 30% occurred four days after the application of spinetoram and spinosad. Thus, chlorantraniliprole and cyantraniliprole are safe options for P. xylostella management since their efficacy favor S. saevissima.