Seasonal Occurrence of the Rice Bug, Leptocorisa spp. On Recommended Rice Varieties

Abstract

population density of the rice bug, Leptocorisa spp. was compared on 5 recommended rice varieties; RD7, RD23, SPR60, SPR90 and CNT1, grown in different seasons. The experiment was conducted with 8 crops during the year 1994-1196 at Lam Luk Ka district, PathumThani province. Each rice variety was grown by wet seeded broadcasting method with plot size, 20x20 meters, and no pesticides application. during the milk stag eof grain formation, the insects were collected by using a sweeping net. Adults and mymphs of the rice bug obtained were counted. The experimental rice varieties were harvested and yields were measured.
Results revealed the occurrences of 2 s[ecies of rice bug, 82.5% of rice bugs collected was L. oratorius while the rest, 17.5% was L. acuta. The insect populations found on the wet-season crop was 2-43 times more than that found on the dry-season crop. If the rice were grown continuously 3 times a year, the insect population was observed to increase during the 2nd and 3rd crops. The rice bug did not express an obvious preference to any rice varieties. However, there was a tendency that more insect population could be found on SPR90 variety. Statistical analysis indicated that population density of the rice bug is highly signifficant negative correlated with the rice yield (60%). That is the outbreak of these insects results the rice yield reduction.