Vertical Distribution and Position of Rice Planthoppers on the Host Rice Plant (Homoptera: Delphacidae)

Abstract

Factors which control the vertical distribution and position of rice planthoppers, Nilaparvata lugens, Sogatella furcifera and Laodelphax striatellus, on rice plants have been studied to determine why N. lugens tend to gather in the lower part of the stem (leaf sheath) of rice plants and why the rice planthoppers settle on rice plants with their head upward. Release of planthoppers on rice plants revealed that N. lugens preferred the lower part of the stem, and that few of them climbed the stem whereas many of them came down from the leaves to the stem. The reasons why N. lugens attack the lower part of the stem can be explained in terms of preference to or sedentariness on it and of downward movement of the planthopper. As for the position of the planthoppers on the rice plant, three factors appear to be associated with the upward position. First, the insects settled on the rice stem with their head oriented to the same direction as the vertical axis of the rice plant. Second, the upward position appeared to be safer than the downward position for planthoppers to support the body weight with their legs. Third, the planthoppers oriented themselves to the light, which comes from above in the field.