Insecticidal control of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is targeted at the adult and nymphal stages, but there is little information on relative susceptibilities of these insects to insecticides. Tarnished plant bug adults were collected from various locations in Mississippi during 2008–2009, and different life stages of their progeny were tested for susceptibilities to three classes of insecticides. A glass vial bioassay was used to evaluate four populations of tarnished plant bugs for susceptibility to the pyrethroid insecticide, permethrin, and two populations to the organophosphate insecticide, methamidophos. Additionally, a diet-incorporated bioassay was used to evaluate the susceptibility of the various life stages of a single population of tarnished plant bugs to a neonicotinoid insecticide, thiamethoxam. For all but one population and insecticide combination, the estimated LC₅₀ values ranked from least to greatest were: 1^st instars, 2^nd instars, 3^rd instars, adults, 4^th instars, and 5^th instars. The tolerances of 5^th versus 1^st instars were greater for populations of tarnished plant bugs exposed to permethrin compared to methamidophos or thiamethoxam. The results of this study indicated that the effectiveness of an insecticide application for the control of tarnished plant bugs depends on the age-structure of the population being treated.