Abstract
The brown planthopper, Nilaparvata lugens STÅL has two distinct wing-forms, macropterous and brachypterous form, which was proved to be induced by the influence of population density during larval development. Here, the author intended to analyze the mechanism of this density effect upon the wing-form determination.
The stimulus inducing the density effect upon the wing-form determination is not only to be the interaction among larval individuals but that of adult individuals of the same species and even adults of the small brown planthopper, Delphacodes striatella.
The mutual stimulation among individual larvae took some parts in determining the wing-form, but it was not the total. The underfeeding during the larval period took another part also. The influence of visual stimulus has no important part in the determination of the wing-form, because percentage of the macropterous female was almost equal with both cases of the rearing under dark or light conditions.
Finally, the difference of the determining factor of the wing-form in both sexes was studied. In female, the brachypterous form was induced largely by the low density. In male, however, it was determined mainly by the climatic factors, such as temperature and day-length. The percentage of the brachpterous male increased under the condition of short day-length and high temperature and under the low temperature irrespective of day-length.
