To assess the toxicity of bifenthrin and four mixtures of insecticides to tarnished plant bug, we used an insecticide dip method of green bean to treat adults of a laboratory colony; mortality was assessed after 48 h. LC₅₀s for imidacloprid, bifenthrin, acephate, thiamethoxam, and dicrotophos were 0.12, 0.39, 0.62, 0.67, and 3.96 ppm, respectively. LC₇₅s for imidacloprid, bifenthrin, acephate, thiamethoxam, and dicrotophos were 0.61, 4.22, 5.10, 2.65, and 7.86 ppm, respectively. Based on the LC₅₀s and LC₇₅s, dicrotophos was much less toxic than the other chemicals tested. PoloMix software was used to determine syngerism, antagonism, or addition effects of the mixtures.Three out of four analyses of the joint action of bifenthrin plus imidacloprid or acephate or dicrotophos showed that toxicity was not independent and not correlated. For bifenthrin plus dicrotophos, observed mortality was greater than expected mortality at most concentrations suggesting synergism. Mixtures of bifenthrin plus imidacloprid and bifenthrin plus acephate showed observed mortality significantly less than expected, suggesting antagonism. LC₅₀s for bifenthrin plus dicrotophos, acephate, imidacloprid, and thiamethoxam were 0.38, 1.06, 0.17, and 0.26 ppm, respectively. LC₇₅s for bifenthrin plus dicrotophos, acephate, imidacloprid, and thiamethoxam were 13.61, 13.18, 0.67, and 0.80 ppm, respectively. Based on the LC₅₀s and LC₇₅s, bifenthrin plus acephate was 3- to 10-fold less toxic than the other chemicals tested. Bifenthrin plus acephate is frequently used in tank mixes to control tarnished plant bug and other cotton pests, and the effectiveness of each individual chemical appears to be reduced in one to one ratio mixtures.