【摘要】 调查100株落叶松,结果表明,兴安落叶松鞘蛾(Coleophora dahurica Flkv.)越冬幼虫和早春第四龄幼虫在树冠上的垂直分布规律是:由下层向上层虫口密度逐渐变小;下层虫口密度通常为上层的2倍以上,最多可达3.2倍。在枝条上的水平分布规律是:当年生枝段上虫数最少,前一年枝段上虫数最多,前二年枝段上次之;前一年枝段上的虫数常为当年枝段上的3倍以上。据幼虫在树冠上的分布规律,讨论了以下问题:①冬季或早春调查虫口密度时,顾及树冠形状,应用“加权法”原理在树冠的上、中、下层调查不同数量样枝,所得结果会更接近于实际;②样枝长度如过短(如:10cm、15cm),所得结果不应用于测报。更多还原

【Abstract】 The vertical and horizontal distribution of larvae of C. dahurica on crown were measured on one hundred trees of dahurian larch (Larix gmelinii) in Harbin forest farm in 1987. The overwintering and fourthinstar larvae distributed from lower level to uper level of crown presented a decrease in number. The average density of larvae on lower crown was twice as much as on uper crown, with the maximum of 3.2 times. Concerned with the horizontal distribution, there were less larvae on the terminal of shoots but most on the section of one year shoots, with medium on section of two years shoots. The larvae density of one year old shoots was 3 times as much as the terminal parts. According to the distribution of larvae on crown, discuss the following problems; 1. When investigating the density of insect population in early spring or winter, the crown should be divided into three layers, each layer sampled different amount of shoots, then weighted, the result close to the real. 2. If the shoot is shorter than 10cm or 15cm, the result can not used for forceast.更多还原