Insect Pests and Natural Enemies on Japonica Rice at Chai Nat Rice Experiment Station

Abstract

The information of insect ecology is necessary and the most important in the IPM. The eclogy of rice insect pests in 4 varieties of japonica rice fields, DOA1, DOA2, Todorokiwse and Shiyonishiki, wee studied at Chai Nat Rice Experiment Station in dry seson of the year 1996 and 1997. Rice were transplanted without insecticide application. Insect funa were collected by D-vac machine starting at 3 weeks after transplanting. Then specimen wee identified and counted in the laboratory. Damages of insect pests and the occurrence of rice bugs in the heading stage of rice were also investigated. They yields of each rice variety were measured after harvesting.
The results revealed low damages of insect pests and no economic loss. The yields obtained are higher than the average. I nthese jponic rice field conditions, the structure of insect components consisted of case of insect pest, 54% were leafhoppers and planthoppers of which the green leafhoppers, Nephotettix spp. were the most abundant (45%). In 1996, 35% of the insect pests collected were the rice bugs, Leptocorisa spp. Their populations on DOA1 and DOA2 vrieties were two times more than those found on Todorokiwse and Shiyonishiki. In 1997, the population of thrips ws found bout 30% of the total insect pests.
Most of prasitioids belonged to the order Hymenoptera. In the case of predators, spiders were the most qabundant at 70%, but their role showed no significant correlation with leafhoppers and planthoppers. However, there was a significant positive correlation (60%) between spiders and other natural enemies. It means ll kinds of natural enemies activated the strengh of biological control of insect pests, and under this condition there is no need to pply insecticides.