Effects of Chilling of Pupae on Subsequent Emergence of Resistant and Susceptible House Flies

Pupae of the house fly (Musca domestica L.) were refrigerated for periods of from 1 to 8 days. Pupae from both DDT-susceptible and DDT-resistant strains were used. The effects of exposure to chilling of pupae were evaluated with reference to exposure interval and (1) numbers of subsequent emerged adults, (2) shifts in adult sex ratios, (3) delay in subsequent emergence. Results obtained from this study indicate that a linear relationship exists between time intervals in which house fly pupae are exposed to chilling and numbers of subsequent emerged adults. An approximate 9% reduction in emergence occurred for each day of exposure to chilling in the susceptible strain tested. A linear relationship also exists between time intervals in which house fly pupae are exposed to chilling and delay in subsequent emergence. Although no significant differences could be demonstrated, as a result of chilling, between susceptible and resistant house flies either in (1) emergence response, (2) deviation in sex ratio, or (3) retardation in emergence, the partial failure of resistant flies to successfully utilize the larval diet is noteworthy. Apparently, limiting factors in the larval diet were more selective against resistant females than against males of either strain.