The effect of temperature on activity of insecticides for controlling grasshoppers in leafy green vegetables was evaluated. Insecticides evaluated had differing modes of action and included diflubenzuron, azadirachtin, Beauveria bassiana, spinosad, endosulfan, esfenvalerate, and naled. We evaluated these insecticides for efficacy to third instars of differential grasshopper, Melanoplus differentialis (Thomas), at temperatures ranging from 10 to 35°C. In the laboratory, treatment with esfenvalerate resulted in 100% mortality at temperatures of 10 to 35°C, and efficacy was not temperature dependent. Treatment with spinosad resulted in similar mortality as with esfenvalerate at all temperatures except 10°C. The activity of B. bassiana was greatest at 25°C and was adversely affected by high and low temperatures. Treatment with diflubenzuron resulted in increased mortality at high temperatures, and at 35°C its activity was similar to that of esfenvalerate and spinosad. The activity of azadirachtin ranged from 19 to 31% and was not influenced by temperature. In field studies, spinosad, diflubenzuron, and esfenvalerate provided differing levels of mortality both at application and when nymphs were exposed to 1-h-old residues. However, only spinosad and diflubenzuron provided similar levels of mortality when nymphs were exposed to 24-h-old residues. The residual activity of endosulfan, naled, esfenvalerate, and spinosad decreased with increasing time (0–24 h) after exposure to sunlight and high summer temperatures. Compared with other insecticides, naled had a short residual activity period and activity was dependent upon immediate contact with the nymphs or their substrate. B. bassiana was inactive under high temperatures and intense sunlight as occurs in summer.