|Budget Amount *help
¥4,800,000 (Direct Cost : ¥4,800,000)
Fiscal Year 1993 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1992 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1991 : ¥3,800,000 (Direct Cost : ¥3,800,000)
The brown plathopper, Nilaparvata lugens exhibits two wing-form, i.e., macropterous and brachypterous wing-form. We have elucidated that wing-form expression is largely regulated by nymphal density, but fundermentally under genetic control, and that there is a great geographical variation in wing-form response to nymphal density. It is well known that the males of this planthopper communicate with females by vibrating their abdomens, and there is also a great geographical variation in pulse repetition frequency (PRF) of the vibration signal. So, in this project, investigations were carried out to eluciate the occurrence mechanism of geographical variation in PRF in relation to wing-form response to density in N.lugens.
The nymphs of N.lugens were reared at different densities in cages with rice seedlings at 25ﾟC under 16L-8D.The males adults obtaind were enclosed in a soundproof chamber, and their vibration signals were recorded by an audio-system which analyzed PRF values. It was found that N.lugens collected in south Asian countries tended to have lower PRF of ca 60 per sec, with higher brachypterous characteristics, while those collected in Japan as immigrants from overseas released vibration signal with higher PRF of ca 80 and became predominantly macropters.
Further, experiments were carried out to generate strains with different PRF as follows : macropterous males with higher PRF and those with lower PRF were selected from high density plot, mated with macropterous females from same density plot. After three generations of selection, these strains became to release vibration signals with significantly different PRF : the strains selected for higher PRF tended to show lower macropterous ratio, while those for lower PRF became to exhibit higher bracyptery, supporting genetic correlation between vibration signal and wing-form expression.