臺灣小稻蝗 (Oxya intricata Stål) 卵寄生蜂之調查

Abstract

小稻蝗（Oxya intricate stål，Acrididae,Orthoptera）主以禾木科植物為食，加害稻、麥、玉米、高粱、甘蔗、甘藷等多種經濟作物。夏秋之間在臺灣稻田時可見到。每年發生2代，以卵期越冬。其成蝗之出現期適與兩期稻作之生長期相遇，因此每期稻作之孕穗至成熟期均蒙受其害，第2期作受害較烈。本調查於民國59至60年間進行，在臺北近郊六張犁、三張犁、景美、萬隆、公葫、中和、松山等地稻田採得小稻蝗卵塊，經過室內飼育與鑑定結果，發現3種卵寄生蜂，即煌卵寄生蜂（Centrodora locustarum Giraud）、稻煌細卵蜂（Scelio oxyao Timber-lake）、廣肩小蜂（Euryrtoma sp.）及1種重複寄生金小蜂（Eupteromalus parnarae Gahan)。本文記述其形態、寄生現象、寄生車及性比率等。 A small rice grasshopper, Oxya intricata Stål (Acrididae, Orthoptera) attacking paddy in Taiwan commonly occurs in paddy fields during summer through winter. It has 2 goner-ations a year and passes the winter in the egg stage. It lays eggs in masses and covers them with a red-brown glummy substance. Egg masses are deposited on rice leaves, among tillers, rice stubble or in the ground of paddy fields, few of them were found on the grasses growing on the paths of paddy fields. The investigations on the egg parasites of Oxya intricata were done during June of 1970 until July of 1971 around Taipei area at Liuchangli, Sanchangli, Chiengmei, Kung- kwan, Wanlung, Hsintien, Chungho and Sunshan. Three primary parasites of O. intricata eggs were obtained and identified as Centrodora locustarum Giraud (Aphelinidae), Scelio oxyae Timberlake (Scelionidae) and Eurytoma sp. (Eurytomidae). A hyperparasite, Eupteromalus parnarae Gahan (Pteromalidae), was found in eggs parasitized by Scelio oxyae and by Eurytoma sp. The observed parasitism in 16,280 field collected eggs averaged 30.72% and 2.28% respectively in the first and second rice crops of 1970. The highest percentage (62.94%) was recorded during late July while the lowest (2.28%) was recorded in December. C. locustarurn was recognized as superparasitism and the dominant parasite in the first crop of 1970. Its egg parasitism was 27.96% in average while parasitism by S. oxyae and Eurytorna sp. were 2.64% and 0.12% in average, respectively. The 3 parasites all showed a ratherlow rate of parasitism in the second rice crop of 1970. The percents of egg parasitism in this second crop were found to be 1.74%, 0.52% and 0.01% in S. oxyae, Eurytoma sp. and C. locustarum, respectively. The number of parasites emerging from one egg of C. locustarum ranged from 4.5 to 41.8 individuals. Observations on sex ratio of these parasites recorded ratios of 3.9:1, 9.3:1 and 3.1:1 in C. locustarurn, S. oxyae and Eurytoma sp. respectively, the figure for females preceeding that for males. The temperature in the laboratory during the studies was maintained at 27 ± 1°C with a relative humidity of 69% in the months of June through August, and 18 ± 1°C with a relative humidity of 71% in the month of December.