Comparison of fertility and effect of population density on fertility between the northern and southwestern Japanese populations of the green rice leafhopper, Nephotettix cincticeps (Uhler) (Hemiptera: Cicadellidae)

Nephotettix cincticeps populations collected at various localities in northern and southwestern Japan were examined to elucidate whether the differences in the fertility and the density dependence of fertility between the two regions were sufficiently large to explain the difference in peak population densities observed in rice fields in the two regions. The experiments consisted of comparison of the fertility among several populations in test tubes or outdoor cages and that of density effects on the fertility between Sado (northern) and Chikugo (southwestern) populations. The result shows that both the population groups were almost similar in fertility as a whole. In the experiments for determining the effect of density on fertility, the numbers of eggs laid per female in the Sado and Chikugo populations were compared at three and four density levels. The linear regression coefficients between the densities and the numbers of eggs laid per female in terms of log-transformed values were similar in both the populations at three density levels, and no significant differences were found between the populations or densities at the four density levels. Therefore, it cannot be concluded that the southwestern populations are less fertile or more susceptible to changes in population density than the northern populations.