水稻瘤野螟族群發生動態與預測

Abstract

瘤野螟為亞洲水稻區重要害蟲之一，該蟲可在台灣越冬而成為翌年之蟲源，但因受低溫及寄主植物等不良環境之限制，越冬蟲量甚低•在誘蟲燈下成蟲一年可出現8個世代，族群高峰分別出現於6月上、中旬及10月中、下旬至11月上旬，兩期作瘤野螟之族群高峰密度相關相常密切（r2=0.7616，p<0.01）。瘤野螟在一、二期稻均可緊衍三個世代，在成蟲侵入稻田繁殖之第一至第二世代幼蟲族群的成長率平均分別為9.75及10.87倍，顯示其族群均呈大幅增長；在第二至第三世代之成長率，於一期稻由0.20至0.26，顯示其密度均較第二世代之密度為低；在二期稻之成長率由2.04至0.005，其中凡水稻移植日期在7月下句者其族群均呈現下降，而8月上旬種植者則呈上升。各世代幼蟲均以危害上位三葉片為主，被害葉高烽一般出現於幼蟲高峰後14天左右。幼蟲的主要危害期在一、二期稻均出現於抽穗至乳熟期，但其危害程度在一期稻據過去12年調查均低於經濟危害基準，而在二期稻則常可超越該危害基準。第二期稻瘤野螟之第一及第二世代成蟲在誘蟲燈之捕獲蟲數與二期稻之被害程度呈密切關係（r2值分別為0.729及0.883)，但直播田、晚植稻以及隔離避風稻田，通常較早植稻為重。二期稻生育初期之成蟲豐度為影響該期稻被害程度之關鍵因素，以該時期或該時期和主要危害期前一世代誘蟲燈之捕獲成蟲數為變數，利用逐步迴歸分析建立預測方程式，其決定係數r2值分別達0.75(p=0.003)及0.98(p<0.0001)，似鵡於中期及短期預測之應用。 The rice leaffolder (Cnaphalocrocis medinalis Guenee) is one of important insect pests of rice in Asia. It can overwinter in Taiwan at very low population due to low temperature and poor host plant conditions. The number of adults catched in light trap appeared 8 population peaks annually. Two distinct maximal peaks appeared during milky to maturing stage of the first and the second rice cropping season, and the latter peak was closely correlated to the farmer one (r2=0.7616, p < 0.01). During each cropping season, the Ieaffolder could complete 3 generations. The larval population growth rate from the first to the second generation was 9.75 and 10.87 in the first and the second crop, respectively, while from the second to the third generation, it ranged from 0.20 to 0.26 in the first crop and 2.04 to 0.005 in the second crop. The earlier transplanting rice usually had lower growth rate as compared with those later transplanting ones. The larvae always injuries on top 3 leaves regardless to the stage of rice, and the peak of injuried leaves usually appeared about 14 days later than of the larval population peaks. However, the main infestation peried occurred during the heading to milky stages of rice, and the severity of infestation during this period in the second cropping season each year was observed to be closely correlated with the number of adult catched in the first and second generation of the cropping season even though the direct seeding rice, and those later planting rice and rice growing in the places sheltering from wind received much severer infestation, Based on the infestation recorded in past 12 years, the damage of this insect in the first cropping season was successively lower than the levels of economic threshold, while that of in the second cropping season was often higher. The population abundance of adult in the initial stage of the crop season was the most important factor to affect the levels of damage in main infestation period. Several equations had been developed for predicting the population abundance as well as the levels of damage of the insect in this study.