Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), is the target for multiple insecticide applications in cotton in the mid-southern U.S. Resistance to several insecticide classes has been documented, so monitoring of resistance levels to insecticides currently used is needed before field control failures occur. Several populations were tested to estimate resistance levels for commonly used insecticides during 2017 to 2019. On average, 25 to 40% of populations were determined to be resistant to thiamethoxam, imidacloprid, and/or sulfoxaflor. There were no differences among years in mean imidacloprid and thiamethoxam LC50 values; however, the mean LC50 increased from 2017 to 2019 for sulfoxaflor. No differences in resistance were detected between the two primary agricultural regions of the Mid-South (Hills and Mississippi River Delta) for any of the insecticides. For each insecticide, the range between the most and least susceptible populations was greatest in the Hills region during 2018. Susceptibility to thiamethoxam was the most variable followed by imidacloprid and sulfoxaflor. It is important to continue monitoring for resistance because continued selection pressure is likely to lead to widespread reduced efficacy in the future.
