Biochemical analysis of 4 rice varieties and a weed showed that the total free amino acid content was greater in the susceptible variety TN 1 than in Ptb 2, Ptb 7 and Ptb 18 which are resistant to both the species of green leafhoppers. However, the weed Leersia hexandra the most suitable host ofNephotettix nigropictus, had the lowest amount of free amino acids. No apparent differences were observed in relation to sucrose, glucose and fructose content in the test varieties. Total phenol content was the highest inLeersia hexandra followed by resistant varieties, while it was the lowest in the susceptible rice variety.
Bioassay of plant extracts in various organic solvents showed that the chloroform and acetone extracts of the resistant variety Ptb 18 were phagodeterrents to either species of green leafhoppers, while the extract of the susceptible variety with the same solvent was phagostimulant. Of the various chemicals bioassayed, sucrose (5%) among the sugars tested, was found to be highly stimulatory for feeding. Among amino acids, serine, alanine and glutamine were feeding stimulatory in nature. On the other hand, most of the amino acid derivatives, all organic acids and phenolic compounds tested exhibited phagodeterrency.