Abstract
The effects of infestation by the white-backed planthopper on the vegetative growth and yield of the paddy rice were studied by field-cage experiments in Chikugo, Fukuoka Prefecture, Kyushu. Rice seedlings were transplanted in late June. Infestation levels were manipulated by changing the planthopper densities to 0, 5 and 10 females per hill. Adult planthoppers were released on caged plants in early July (13 days after transplanting) and late July (31 days after transplanting). To quantify the separate effects of oviposition damage by female immigrants and sucking damage by subsequent progeny, insecticide spray plots were used at each treatment. The plant height and number of tillers of infested rice plants were significantly reduced until the maximum tillering stage, when the planthoppers were released in early July. Growth differences between infested and uninfested plants disappeared gradually towards the heading stage. The yield, number of panicles, number of spikelets per panicle, percentage of filled spikelets and weight of 1, 000 grains, were measured at harvest. No correlation was observed between the initial released planthopper density and yield. The infestation by the second generation (early to mid-August) decreased the yield and number of spikelets per panicle.
