SUMMARYThe toxicity of the carbamate insecticides Sevin(R), Zectran(R) and B 37344 (4-methylthio-3,5-xylylN-methylcarbamate) to worker honeybees (Apis mellifera) was investigated at 60°, 80°and 90°F. [16,27, 32°C.]. All compounds exhibited a negative temperature coefficient of toxicity. This was most pronounced in Sevin which was 3.81 times as toxic at 60°as at 80°F. Application of the synergist piperonyl butoxide enhanced the toxicity of the carbamates to levels roughly corresponding to their intrinsic toxicity and decreased the influence of the post-treatment temperature on toxicity. The results suggest that a carbamate-detoxification mechanism, sensitive to temperature and the action of piperonyl butoxide, is present in honeybees. The significance of this mechanism deserves further consideration as it might suggest optimum times for the application of the insecticides which would prevent high losses of honeybees.