译 名：
THE PARASITES OF THE RICE GALL MIDGE (ORSEOLIA ORYZAE (WOOD-MASON) ) IN KWANGTUNG PROVINCE AND THEIR SUSCEPTIBILITIES TO INSECTICIDE APPLICATIONS
作 者：
LIU SIU-KING, HUANG DUAN-PING, CHIU SHIN-FOON (Department of Plant Protection, South-China Agricultural College)GU SIU-WEI (Institute of Entomology, Kwangtung Province)
摘 要：
During the last four years the authors have conducted a series of investigations on the collection, rearing and identification of the parasites of the rice gall midge in Kwangtung Province. Preliminary observations on the bionomics of the parasites and experiments on the effect of insecticides on them were also carried out. The results of studies obtained are summarized as follows:1. Altogether 5 species of hymenopterous parasites on the rice gall midge have been found in Kwangtung Province. They are:Platygaster sp. (gregarious endoparasite)Platygaster sp. (solitary endoparasite)Neanastatus grallarius MasiNeanastatus oryzae PerriereObtusiclava oryzae Sabba RaoThe morphology of the various stages of these parasites are described and a brief account of their bionomics is also given. Usually the gregarious Platygaster parasite is the predominant species, but during the seedling and tillering stage of the late crop (both in the seed-beds and in the field) the population of Neanastatus may increase to as high as 70-80% of the 5 species in total. These parasites possess different characteristics in biology and play different roles in suppressing the outbreaks of the rice gall midge. Further investigations will help us to know how to utilize these parasites in the program of integrated pest management in rice fields.2. The percentage of parasitism of the rice gall midge in the seed-beds and fields of the late crop was found to be very high, in some cases as high as, 90% or more. This contributes an important factor in controlling populations of the gall midge. The outbreak of the gall midge is closely correlated to the cropping system; the late crop and the triple rice crop afford a "bridge" for the favorable reproduction of the gall midge. The irrational application of insecticides kills the natural enemies and is also one of the factors leading to the resurgence of the insect pest.3. According to the investigations made in 1976 in San-Hua brigade, Hua county, the percentage of parasitism on the rice gall midge in the overwintering generation in the wild rice (Oryzae rufipogon) reached as high as 65%, and in the first aad second generations of the early crop the parasitism was found to vary from 32.5% to 33.3%. But in the seed-beds of the late crop, due to the frequent applications of insecticides, usually with a spraying of Methyl parathion-BHC and Dimethoate at an interval of 4-5 days, the percentage of parasitism dropped to 1.53-4.5%, whereas in the field with no insecticide treatment it was about 44%. This indicates that the conventional method of the application of insecticide produces adverse effects to the parasites.4. Laboratory experiments were carried out to determine the toxicity of several insecticides to the parasites of the rice gall midge. As a contact poison the organophosphorus compound Pyrimioxythion (N-23) was the most toxie, and chlorodi-meform was the least toxic. The order of toxicity to Platygaster sp. was: Pyrimioxy-thion > Trichlorofon > Dimethoate > (2,5-Dimethylphenyl-N-methylcarbamate) > Chlorodimeform. The LC50 of the five compounds was estimated to be 1.1, 3.5, 5.5, 15.0 and 24.0 ppm, respectively. As a foliar spray, Pyrimidoxythion is also more toxic than Methyl parathion-BHC to Obtusiclava oryzae and Neanastatus spp. The formulations and methods of applications of the insecticides is very important to the protection of the parasites. As a rule, broadcasting of impregnated-dusts is less hazardous to the natural enemies and the root-zone method of application givea good protection to the parasites and the spiders in the rice field. Thus there is a possibility that the rational use of insecticides will help to increasing the stability of the paddy agro-ecosystem and it may be of great utility in developing an efficient integrated control program for the rice gall midge as well as other insect pests.
