Macropterous and brachypterous females of the brown plant-hopper, Nilaparvata lugens STAL, which had been obtained from a standard mass culture were kept either in pairs or in crowds on fresh or withered rice seedrings, and their progeny was reared at three densities, 1,3,and 5 individuals per tube, throughout the larval period. In comparison of the progeny of the macropterous female (A) and those of the brachypterous female (B), A<B in the mortality of the larvae when they were reared at the lowest density (the reverse was true at the highest density), A<B in the percentage of brachypterous females at the highest density, and A<B in the larval period at every density. A more detailed investigation suggested that the relative length of the successive larval stages of the progeny larvae was different in both maternal lines. The effects of rearing in crowd appeared on the percentage of brachypterous females of the progeny of the brachypterous females and on the larval period of the progeny of the macropterous females. In either of the maternal lines, rearing of adult females under poor food conditions resulted in raising of the mortality, lowering of the percentage of brachypterous females, and prolongation of the larval period in their progeny.
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