The toxicity of dimethoate and acephate to tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), collected from 5 locations with high levels of insecticide use in the mid-Delta of Mississippi, and 2 locations of low insecticide use outside the Delta, was determined in the laboratory. Tarnished plant bugs collected in the Delta in late-May or early-June were as much as 4.8 times more tolerant to dimethoate as compared to those from the non-Delta locations. Tolerance to dimethoate in plant bugs collected in the Delta during mid-October declined at most locations but was still 2 to 3 times higher than in the non-Delta locations. Little tolerance to acephate was found at any location for plant bugs collected in the spring or in the fall.