Temporal variations in the reproductive condition of Drosophila obscura Fallén and D. subobscura collin.

The reproductive condition, insemination status and fat content of Drosophila obscura and D. subobscura were investigated in samples from natural populations, and in near-natural and artificial experimental situations. In Northern England D. obscura populations pass through either three of four generations per year, one of which includes a period of adult diapause which involves both reproductive condition and fat content. Appropriate day lengths lead to both the initiation and the breaking of this diapause. D. subobscura populations develop continuously and pass through from four to six generations per year. Females from both species were only rarely fertilised when immature. The dependence on both season and food-regime of development, rates in the various stages of both species have been examined and discussed.