Abstract
In order to clarify their ability to over winter, the eggs, full grown larvae and 1-day-old pupae of Musca domestica, Phormia regina and Aldrichina grahami, were exposed to low temperatures from 8 down to 4℃. 1. The mortality of immature stages of flies was increased by lowering the temperature of exposure and by increasing the duration of the exposure period. 2. In general, the larva was the most tolerant stage to cold temperatures. Eggs, in comparison to larvae and pupae, were less tolerant. Exposure days required for 50% mortality in immature M. domestica exposed to 4℃ were 1.6-3.7,2.5-3.3 and 2.7-3.8 days for eggs, larvae and pupae, respectively. Those of P. regina were 2.1-2.6,10-13 and 3.6-5.5 days respectively, and those of A. grahami were 4.1,13 and 6.2 days. 3. A. grahami was the most tolerant to cold temperatures among three species of flies, followed by P. regina and M. domestica. 4. The tolerance to cold temperatures of M. domestica and P. regina which were collected from different districts were compared. The strains used in the experiment are as follows : M. domestica from Takatsuki, Nara, Tongduchon (Korea) and Bangkok (Thailand), and P. regina from Akita, Tokyo and Samegai. In the four M. domestica strains, the mortality of larvae exposed to cold temperatures was found to be significantly lower in the Bangkok strain than in other strains. In the three P. regina strains, the mortality of pupae was found to be significantly higher in the Akita strain than in the Tokyo and Samegai strains. 5. It is suggested that only an extremely small number of immature stages of flies overwinter in temperate climatic regions.
