沙棘木蠹蛾卵和幼虫空间分布的地统计学分析

沙棘木蠹蛾(H olcocerushippophaecolus Hua,Chou ,Fang et Chen)是近几年在内蒙古、辽宁、山西、宁夏和陕西等地大面积爆发的一种钻蛀性害虫,其危害发生在幼虫期,主要危害沙棘(H ippophae rhamnoidea)的根干部。为了有效地控制其危害,深入了解种群的空间结构,利用地统计学方法分析了两种受害程度不同的林分内沙棘木蠹蛾幼虫种群和重度受害林分内卵块的空间分布特性。结果表明:两种受害程度不同的林分内,沙棘木蠹蛾的危害具有显著差异,轻度受害林分内无虫样本所占的比例较大,达70 % ,而重度受害林分内不到2 0 % ;虫口密度在轻度受害林分内超过6头/株的只有6 .9% ,而重度受害林分内高达31.9%。根据全方向的变异函数曲线图分析得知:重度受害林分和轻度受害林分内幼虫种群的空间依赖范围分别为7.3m和87.4 18m,而局部空间连续性强度分别为0 .914和0 .178。重度受害林分内幼虫表现较强的空间聚集性,而轻度受害林分则表现为随机分布。在重度受害林分中,单株沙棘树上沙棘木蠹蛾卵块数量最多的为11个,最少的为1个,有卵株率达72 %。分别采用四种不同的理论模型来拟合卵块的实际变异曲线图,得知其全方向的变异函数曲线为指数型,空间依赖范围大小为3.6 m,局部空间连续性强度为0 .876 ,卵块在重度受害林分中呈现较强

Geostatistical analysis on spatial distribution of Holcocerus hippophaecolus eggs and larvae

The seabuckthorn carpenterworm, Holcocerus hippophaecolus Hua, Zhou, Fang et Chen has been a severe boring pest of seabuckthorn in Inner Mongolia Autonomous region, Liaoning, Shanxi, Ningxia and Shaanxi provinces in China in recent years. Larvae cause damage primarily to stems and roots of seabuckthorn. Spatial characteristics were analyzed using geo-statistical methods for population of carpenterworm larvae in two woodlands with different damage levels and egg masses in heavily-infested woodland in order to effectively control the insect and to further study the spatial distribution of its population. The result showed that the damage level caused by the carpenterworm differed significantly in the two woodlands. Only 20% of trees in lightly-infested woodland were infested compared with 70% in heavily-infested woodland. The percentage of trees with 6 or more larvae was 6.9% for the lightly-infested woodland and 31.9% for the heavily-infested one. Analysis of the isotropic variogram indicated that the distance of spatial dependence of the carpenterworm larvae was 7.3 m in the heavily-infested woodland and 87.418m in the lightly-infested one, while the intensity of local spatial continuity was 0.914 and 0.178, respectively. Intense spatial aggregation of larvae was observed in the heavily-infested woodland, while random distribution was observed in the lightly-infested one. In the heavily-infested woodland, 72% of trees were found to have egg masses, ranging from 1 to 11 per tree. We used 4 different types of theoretical models (spherical, exponential, Gaussian, and linear will sill) to represent the observed spatial correlation of egg masses and found that the exponential isotropic model fit best with 3.6 m spatial dependence and 0.876 intensity of local spatial continuity. Intensive spatial aggregation of egg masses was found in the heavily-infested woodland. The aggregation was primarily centered at the center of the woodland and spread from there to the entire woodland.