Feeding damage of green rice leafhopper, Nephotettix cincticeps Uhler (Hemiptera: Deltocephalidae) on the rice [Oryza sativa] plant in Hokuriku district [Japan], 1: Effects of sap-feeding on the growth and yield of rice plant in the paddy fields

The effects of sap-feeding of green rice leafhopper (GRL) on growth and yield of rice plant in the paddy fields of early variety 'Koshijiwase' or 'Toyamanishiki' were evaluated from 1982 to 1986 without in 1984. The density of blocks established in the paddy fields were induced three levels (high, middle and low) by application of insecticides and releasing of adults or nymphs. In high density blocks, the number of GRL rapidly rosed from mid-August and increased to about 10,000 individuals per 20 times sweeping on late-August in 1982, 1985 and 1986. In 1983, on the other hand, the growth of density proceeded earlier from mid-July and increased to about 4,000 individuals, on beginning of August. After that nearly density was kept during August. The adults and nymphs of GRL in middle or low density blocks occurred similarly, but the number of individuals were controlled less than established levels. The ear length and culm length just before the harvest time were measured also. No significant differences were recognized among the values of high, middle and low density blocks. It was concluded that the growth of rice plant was little affected by sap-feeding of GRL. For estimating the yield of each block, rice plants were reaped in 3.3 m2. In high density blocks, percentage of ripened grain and weight of hulled rice were lower and weight of rice screenings was higher than that in low density blocks. The reduction of yield and yield component in the high density blocks must be regarded as the repression of ripening by sap-feeding of GRL. Nearly 5 % yield losses in high density blocks were estimated in 1982, 1985 and 1986. On the other hand, the decrease rate of yield were about 23 % in 1983. Severe damage suffered in 1983 was due to high density of GRL earlier from beginning of August. The tendency that GRL attacks rice plant earlier, severer damage suffered was confirmed by releasing adult females into a hill covered by net bag in the first or latter half of filling period. The experiment was carried out in a medium variety 'Koshihikari' field in 1983. The density of GRL was lower than that of early varieties. However, the decrease rate of yield was relatively high i. e. attained about 10 %