陕西省栎黄枯叶蛾蛹的空间分布

栎黄枯叶蛾(Trabala vishnou gigantina Yang)是近年来在陕西吴起沙棘林中大面积暴发的一种食叶害虫,为了解其种群空间结构,有效控制危害,利用地统计学等方法,对不同坡向和疏密度沙棘纯林中的栎黄枯叶蛾蛹的空间分布进行了研究。结果表明:栎黄枯叶蛾化蛹的高峰期为8月中旬,雄性幼虫较雌性幼虫平均早3.7 d化蛹;蛹在阴坡的东南向和阳坡的西、北两方向分布比例最大;在距沙棘树基部30.00—75.00 cm范围处分布密集。由全方向的变异函数曲线分析得知:阴坡密林、阴坡疏林、阳坡密林、阳坡疏林中,栎黄枯叶蛾蛹的空间依赖范围分别为95.609、47.379、79.238、42.415 m,空间变异值分别为0.760、0.561、0.649、0.407;且在阴阳两坡向的密林中均呈聚集分布,疏林中均呈随机分布。用Kriging插值方法生成的空间分布图显示蛹在空间分布上存在一定的边缘效应,且方向性较明显。

Spatial distribution of Trabala vishnou gigantina Yang pupae in Shaanxi Province, China

Trabala vishnou gigantina Yang (Lepidoptera: Lasiocampidae) is one of the most important defoliators in China. Larvae of T. vishnou gigantina feed on tender leaves primarily causing damage to the crown layer. In the last few years, the use of single species plantations combined with poor management and a lack of adequate monitoring and early warning has allowed populations of this pest to erupt and cause serious damage in Hippophae rhamnoides L. forest stands in Wuqi County, Shaanxi Province, China. Spatial distribution is one of the most important properties of insect populations. It provides dynamic information about insect populations, describes individual associations, and allows the prediction of variations in spatial distribution patterns. Geostatistical methods provide very powerful tools for explaining the spatial distribution of many species. These methods allow both the direct measurement of spatial distribution of organisms and tracking of changes in distribution over time because the exact location of the species has been documented at a specific point in time. To further investigate spatial distribution and effectively control this pest species, spatial distribution patterns of T. vishnou gigantina pupae were analyzed using geostatistical methods in pure H. rhamnoides forests with different slopes and densities. Results show high levels of pupating occurred mainly in mid-August. Also, males pupated 3.7 days earlier than females. Pupae were also widely distributed on southeastern facing shady slopes, and on west and north facing sunny slopes. Pupae gathered mainly at heights of 30-75 cm on trees. Analysis of isotropic variograms indicated T. vishnou gigantina pupae spaced themselves 95.609, 47.379, 79.238, and 42.415 m apart in densely forested shady slopes, open forests on shady slopes, densely forested sunny slopes, and open forests on sunny slopes, respectively, while the intensity of local spatial continuity was 0.760, 0.561, 0.649, and 0.407, respectively, in the above stands. Also, semivariogram analysis revealed the Gaussian model had the best fit to T. vishnou gigantina pupae distributional patterns in dense forests, implying an intense spatial aggregation pattern, while the linear model fitted best with the open forest, implying a random distribution. As the maps with Kriging interpolation described, T. vishnou gigantina pupae exhibited an edge effect and an obvious directional distribution; the pupae had a clustered distribution at the edge of the plantation and occurred in point locations scattered inside the plantation. Numbers of clustered plaque gradually declined toward the center of the forested area. This was reflected in the tendency of the pupae to cluster together on a spatial scale, and in the direction of their proliferation. Currently, T. vishnou gigantina infestations are most commonly controlled using chemical pesticides. However, H. rhamnoides is an economically and ecologically important plant, so residues need to be considered when spraying pesticides. Based on the spatial distribution characters, we suggest picking the pupa manually on the sunny slopes and especially on the edges of seabuckthorn plantations at a height of 30-75 cm to limit reproduction of this pest species. Research results demonstrate the spatial distribution patterns of T. vishnou gigantina pupae in pure H. rhamnoides forests, providing a theoretical basis and practical guidance for controlling populations of this insect pest. This research will provide a meaningful foundation for integrated pest management.