Honeydew excretion measurement techniques for determining differential feeding activity of biotypes of Nilaparvata lugens on rice varieties.

Techniques to quantify the feeding activity of Nilaparvata lugens (Stal) on rice varieties as based on honeydew excretion are described and their potential as a bioassays for biotype identification are discussed. Honeydew, excreted on filter paper, was stained with ninhydrin and quantified by measuring the area (mm2) or by weighing. Results were satisfactory but the methods were extremely tedious. Volumetric measurement of honeydew with micropipettes was less sensitive. The color intensity of one μliter honeydew streaked on filter paper and treated with 0.001% ninhydrin was determined with a FujioxTM Densitometer. The method was relatively simple and rapid and was sufficiently precise for biotype identification as based on differential feeding activity.