Abstract
It was observed by UTIDA (1954) and CASWELL (1960) that the percentage of emergence of the flight form decreased gradually from generation to generation in the breeding population of southern cow pea weevil, Callosobruchus maculatus. In the present study, this secular trend of decrease in the percentage of the flight form was demonstrated experimentally in both cases where the population started from the non-flight form or the flight form. The percentage took rather higher values at the initial five generations and after that it decreased and kept to a low level. After continuing the breeding in the experimental condition for over two years, the percentage droped to 0 to 2. A genetical factor ought to be considered for the explanation of the results obtained, though the flight form is induced phenotypically by the influence of the some environmental factors such as high temperature, low content of water in the larval food, larval crowding, and so on. Waddington's theory of genetical assimilation (1953) and the natural selection seem to be pertinent to elucidate the present finding. It can be assumed that the results obtained in the present experiment is an example of the evolving process of the young species which have adapted to environments of stored beans or cereals that have recently been turned out by man.
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