幼虫寄生对稻纵卷叶螟田间种群控制作用的评价

稻纵卷叶螟是水稻常见害虫之一,在菲律宾包括3个种,即Cnaphalocrocis medinalis、Maras-mia patnalis和M.exigua。根据1989年雨季在吕宋岛两个不同地区的调查,共记载了15个初寄生和2个重寄生性天敌,其优势种主要寄生2或3龄幼虫,杀死寄主在5龄之前。用值k和Bellows(1981)的密度制约模型分析表明,幼虫寄生作用是稻纵卷叶螟田间种群的一个直接密度制约死亡因子,这种作用属补偿不足(b<1),并具有时滞效果。讨论指出,在调查时应避免使用某一时刻寄生率,来评价寄生性天敌的作用,而需要综合考虑寄主密度及随时间而变化的条件。

AN EVALUATION ON THE SUPPRESSIVE EFFECT OF LARVAL PARASITIZATION ON THE POPULATION OF RICE LEAFFOLDERS

In the field studies in Victoria, Luguna and Zaragosa, Nueva Ecija of the Philippines during the wet season (July-November) of 1989, a total of 15 primary larval parasitoids were recorded on the rice leaf folder complex (Cmaphalocrocis medfnclis ,Marasmia patualis and M. exigua). The predominant species (e.g. Cardiochiles pailippinensis, Macrocentrus sp. and Temelucha philippinensis) mainly attacked the 2nd and 3rd instar larvae and killed the host before 5th instar. The Bellow's model (1981) was used to analyze the density relationship between the host and its parasitoids. The mortality caused by larval parasitization, expressed as a k-value, was found to be directly density-dependent, time delayed as well as under-compensative. It is suggested that evaluation on the effectiveness of a natural enemy should consider not only the percent parasitism, but the host density, host behavior and the susceptibility changes due to parasitization as well.