The rate of development ofCorythucha morrilliOsborn and Drake was measured at seven temperatures on guayule,Parthenium argentatumGray. At 60% RH and 16-h light cycle the time required for development from egg to adult ranged from 34.7 days at 20°C to 17.3 days at 30°C. Little nymphal development occurred at 17.8°C, and no eggs or nymphs developed at temperatures exceeding 34.4°C. Egg and nymphal survival were greatest at the median temperatures.