Abstract
The effects of amino acids, sugars, and purine-pyrimidine bases on sucking response were examined for the brown planthopper, Nilaparvata lugens (STÅL). For this purpose, the number of honeydew droplets excreted and stylet sheaths produced by the female adults feeding on the aqueous solution of different compounds during the test period were counted, and the ratio of the honeydew droplets to stylet sheaths was used as an index to evaluate their phagostimulative effect. Of the amino acids tested in 1% concentration, L-aspartic acid, L-glutamic acid, D-aspartic acid, L-alanine, L-asparagine, and L-valine evoked a significantly stimulated sucking response. Generally they caused a reduction in the stylet sheath formation, but enhanced the honeydew excretion. Several kinds of mono- and oligosaccharides including sucrose also stimulated sucking, although to a lesser degree, at a concentration of 5%. Furthermore, sucrose was found to synergize the phagostimulative activity of L-aspartic acid, L-glutamic acid, L-alanine, and L-asparagine. Four kinds of prine-pyrimidine bases showed no effect at 0.05% concentration. Basing on these results it seems likely that the free amino acids occurring in the rice plant such as L-aspartic acid, L-glutamic acid, L-alanine, L-asparagine, and L-valine play a major role in the sucking behavior of the brown planthopper.
