Parasitic Activities of Egg Parasitoids on the Rice Planthoppers, Nilaparvata lugens(STAL)and Sogatella furcifera(HORVATH)(Homoptera:Delphacidae), in the Muda Area, Peninsular Malaysia

抄録

Natural enemies of the eggs of the rice planthoppers Nilaparvata lugens and Sogatella furcifera were investigated in two direct-sowing paddy fields of the Muda area during the main cropping season in 1989. Egg mortality was estimated with a "trap method" in which "trap plants" with planthopper eggs were exposed in the fields, and field sampling of eggs. Mortality in egg stage varied from 23% to 92% in N. lugens, and from 11% to 90% in S. furcifera. Parasitism by wasps was the major mortality factor in the egg stage. The parasitoids Anagrus and Oligosita emerged from both planthopper eggs. In N. lugens eggs, Anagrus spp. were predominant when the rice plants were young. The parasitism by Oligosita spp. increased with growth of the rice plants. In S. furcifera eggs, Anagrus spp. were predominant throughout the crop season. The maximum parasitism rates were 68% in N. lugens eggs and 69% in S. furcifera eggs. Significant differences between the two methods were detected in only two cases. Parasitism indicated by the trap method reflected the actual state of parasitism in the field fairly well.