Toxicity Assessment of Diafenthiuron Against Adults of <i>Sitotroga cerealella</i> (Lepidoptera: Gelechiidae)

The Angoumois grain moth, Sitotroga cerealella, is a major pest of stored cereals, causing concealed damage that reduces both yield and grain quality. This study evaluated the toxicity of Diafenthiuron (Polo® 500 SC) against adult S. cerealella under controlled laboratory conditions using a residual contact bioassay. Eight concentrations of the insecticide were tested, and mortality data were analyzed using probit analysis. The median lethal concentration (LC₅₀) was estimated at 2133.25 ppm with 95% confidence limits of 1639.71 to 2754.11 ppm. The regression slope of 1.126 ± 0.101 indicated a moderately steep dose–response relationship, while the chi-square value of 5.432 with six degrees of freedom and a heterogeneity factor of 0.905 confirmed that the probit model provided a good fit to the observed mortality data. No mortality was observed in the untreated control group, validating the reliability of the experimental procedure. Mortality increased progressively with rising concentrations, demonstrating a clear dose-dependent response. These findings provide important baseline susceptibility data that can support resistance monitoring in laboratory colonies with repeated exposure to Diafenthiuron and offer a reference for future toxicological studies on stored grain pests under laboratory and semi-field conditions.