A comparison of mortality, developmental time, and pupal weight was made for Mexican bean beetle larvae reared on three stages of soybeans and reproductive stage lima beans in 12 constant temperature and relative humidity (RH) conditions. At high humidities and favorable temperatures (17, 22, and 27° C) there were no significant differences in survival to the pupal stage on the various host plants. On lima bean foliage, larval survival was not significantly influenced by moisture stress. However, survival decreased on all soybean hosts as temperature increased, or as RH decreased, and was inversely proportional to vapor pressure deficit. These stresses are also reflected in larger development times and lower pupal weights. Survival at 32° C in all cases was low. Female larvae appear to be more capable of enduring conditions of moisture stress than males. Stress due to adaptation to change in RH was also observed.