EFFECT OF ORGANIC RICE FARMING ON LEAFHOPPERS AND PLANTHOPPERS .2. AMINO-ACID CONTENT IN THE RICE PHLOEM SAP AND SURVIVAL RATE OF PLANTHOPPERS

Nitrogen content of rice plants was compared among chemically fertilized, poultry-mamured, non-fertilized and organically farmed rice fields to clarify factors of a comparatively lower population density of planthoppers in the latter. The nitrogen content of rice plants was found to be the lowest in the organically farmed field. The content of amino acids in the phloem sap of potted rice plants was compared between the chemically and the organically fertilized cultivations. The amount of total amino acids tended to be smaller in the plants from the organic cultivation. The content of the asparagine was significantly lower in the organically cultivated plants. In pot experiments, the survival rate of the nymphs of Nilaparvata lugens and Sogatella furcifera was lower in the organic plant than in the chemically cultivated ones.