EFFECTS OF ORGANIC FARMING OF RICE PLANTS ON POPULATION-DENSITY OF LEAFHOPPERS AND PLANTHOPPERS .1. POPULATION-DENSITY AND REPRODUCTIVE RATE

We studied the effects of organic farming of rice plants in a paddy an d in a chemically-fertilized plot, a poultry-manured plot and a non-fe rtilized plot on the population densities of the green leaf-hopper, Ne photettix cincticeps UHLER, the white-backed planthopper, Sogatella fu rcifera HORVATH, and the brown planthopper, Nilaparvata lugens STAL. T he density of the green leafhopper in the organically-farmed paddy was the lowest probably due to the low population density during the fall ow period. The density of the white-backed planthopper in the organica lly-farmed paddy was the lowest because the reproductive rate was extr emly low. The density of the brown planthopper in the organically-farm ed paddy was also the lowest. The density of natural enemies in the or ganically-farmed paddy was lower or similar to that in the other plots . Therefore, natural enemies did not contribute to the lower density o f leafhoppers and planthoppers in the organically-farmed paddy.