Semi-quantitative biochemical analyses by paper chromatography–densitometry and pH determinations of honeydew excreted by Nephotettix virescens (Distant) feeding on rice plants revealed higher free amino compound and sugar concentrations in honeydew excreted on the susceptible variety TN1 than on resistant ASD7 or P203. Furthermore, sap exudates from these three varieties, presumed to be mainly from xylem, as well as honeydew excreted on the resistant varieties were acidic, whereas honeydew from TN1 was predominantly basic. Since phloem sap in herbaceous plants usually gives an alkaline reaction whereas xylem sap is acidic, and because the former contains much higher concentrations of sugars and free amino acids than the latter, the biochemical evidence strongly suggests that Nephotettix virescens is primarily a xylem feeder on the resistant plants tested, but feeds predominantly on phloem sap in susceptible TNI.
