ANTIFEEDANT EFFECTS OF PLANT-LECTINS AND AN ENZYME ON THE ADULT STAGE OF THE RICE BROWN PLANTHOPPER, NILAPARVATA-LUGENS

The feeding activity of adult rice brown planthopper, Nilaparvata lugens (Stal) on selected proteins incorporated into artificial diets was examined, based on quantitative analysis of honeydew excretion, in order to determine the mechanism of action of antimetabolic proteins towards homopteran pests. The lectins Galanthus nivalis agglutinin (GNA), wheat germ agglutinin (WGA) and the enzyme soybean lipoxygenase (LPO), previously demonstrated to be toxic to this insect, reduced honeydew excretion levels of adult Nilaparvata lugens over a 24 h period when incorporated into artificial diet at 0.1% {w:v}, indicating that these proteins acted as antifeedants. Of the proteins tested GNA was the most effective antifeedant, reducing honeydew droplet production by 96%, although after 24 h there was some recovery in the honeydew excretion levels and thus the insects appeared to tolerate the presence of the antifeedant with time. The lectin Pisum sativum agglutinin (PSA), previously demonstrated to be non-toxic, showed no antifeedant properties.