Pupae (pharate adults) of the housefly Musca domestica show a rapid cold-hardening response in which transfer from 27 to -7-degrees-C for 2 h is lethal whereas prior acclimation at 0-degrees-C for only 3 h is sufficient to confer a high level of cold tolerance against subsequent exposure to -7-degrees-C for 2 h. When pupae were acclimated at 0-degrees-C for 3 h (= acclimated) or acclimated at 0-degrees-C for 3 h and then transferred to -7-degrees-C for 2 h (= cold shocked), the mean longevity of emerging females in both groups was 5 days less than in a control population. The mean daily oviposition of the cold-shocked females was also reduced by five eggs per day compared to the acclimated and control groups. The combined effects of a shorter life span and lower daily oviposition produced a significant reduction in mean total fecundity from 623 +/- 73.6 (control) to 345 +/- 54.9 (cold shocked) eggs per female. Additionally, the mean daily emergence of flies from eggs laid by the cold-shocked group was 14.2% lower than in the control. In all treatment groups egg viability decreased during the reproductive life of the female parent. These results suggest that rapid cold hardening and cold-shock exposure can reduce adult longevity. However, the acclimation response ensures survival in brief exposures to moderately low temperatures in a high proportion of the population that would otherwise die, providing an adequate base for population increase on return to more favourable conditions.
