Various pesticides directly impact insect pest populations through acute toxicity (lethal) effects, but they also cause a range of indirect (sublethal) effects on pest physiology or behavior. In this study, we describe both lethal and sublethal effects of endosulfan on the survival, development, and fecundity of Apolygus lucorum Meyer-Dür (Hemiptera: Miridae), an important pest of Bacillus thuringiensis (Bt) cotton, Gossypium hirsutum L., in China. We quantify pesticide effects on adult mirids as well as on subsequent (F1, F2) generations. Toxicity bioassays determined the median lethal concentration (LC₅₀) for adult A. lucorum as 0.58 ppm. To evaluate the sublethal effect of endosulfan, we used LC₂₀ and LC₄₀ concentrations at 0.30 ppm and 0.48 ppm, respectively. Sublethal concentrations of endosulfan significantly reduced longevity and fecundity of female adults, but slightly affected male longevity. We also found sublethal effects on the F1 generation, through a reduction of egg hatching rate, nymphal mortality, adult molting rate, and adult fecundity, and on the F2 generation, through a decrease of egg hatching rate. These results show that endosulfan has far greater effects on A. lucorum than estimated by acute toxicity tests, and the effects of this pesticide on surviving mirids can be comparatively long-lived. This pesticide likely causes severe disruptions of A. lucorum population dynamics, with single endosulfan application, invoking a great reduction of population growth of resident mirid populations. We discuss implications of this work for control programs for A. lucorum on Bt cotton.