Park Yong-Lak, Tollefson Jon J
Department of Entomology, University of California, Riverside, CA 92521, USA.
J Econ Entomol. 2005 Apr;98(2):378-83. doi: 10.1093/jee/98.2.378.
The dispersion of root injury to Zea mays L. by corn rootworm, Diabrotica spp., larvae was characterized using geostatistics to determine the appropriate sampling distance to obtain independent estimates of root injury. We also investigated the effect of the root injury levels on the spatial dependence of root injury at three different spatial scales: large-scale study with 25-m sampling distance in three, 8-ha fields; moderate-scale study with 0.2-m sampling distance in six, 2-ha fields; and small-scale study with exhaustive sampling in eight, 12-m(2) plots within cornfields. In the large-scale study, a nugget model best fit the semivariograms, indicating the dispersion of root injury exhibited a random pattern. In the moderate-scale study, all the semivariograms were best fit with an exponential model, and 68 to 96% of the variability was explained by spatial dependence, suggesting a high degree of spatial aggregation of corn root larval injury. The ranges of semivariograms fell within < 4 m, except one field that had the range of 14.7 m. In the small-scale study, the Gaussian, exponential, or spherical models fit the semivariograms best and 50 to 89% of the variability was explained by spatial dependence, suggesting spatial aggregation of root injury. The ranges of semivariograms were from 0.35 to 1.04 m. In the small-scale study, the degree of spatial dependence increased significantly (P < 0.05) as the average root injury increased within the range of root injury observed in the study. These results suggest that the minimum distance between root samples in small-plot insecticide trials should be > 1 m within a row to obtain unbiased estimates of root injury.
利用地统计学方法对玉米根萤叶甲（Diabrotica spp.）幼虫对玉米（Zea mays L.）根系造成的损伤扩散情况进行了表征，以确定合适的采样距离，从而获得根系损伤的独立估计值。我们还在三个不同空间尺度上研究了根系损伤水平对根系损伤空间依赖性的影响：大规模研究中，在三块8公顷的田地中以25米的采样距离进行；中等规模研究中，在六块2公顷的田地中以0.2米的采样距离进行；小规模研究中，在玉米田内的八块12平方米的地块中进行详尽采样。在大规模研究中，块金模型最适合半变异函数图，表明根系损伤的扩散呈现随机模式。在中等规模研究中，所有半变异函数图均最适合指数模型，且68%至96%的变异性可由空间依赖性解释，这表明玉米根幼虫损伤具有高度的空间聚集性。除了一块范围为14.7米的田地外，半变异函数图的范围均小于4米。在小规模研究中，高斯、指数或球形模型最适合半变异函数图，且50%至89%的变异性可由空间依赖性解释，表明根系损伤存在空间聚集性。半变异函数图的范围为0.35至1.04米。在小规模研究中，在所研究的根系损伤范围内，随着平均根系损伤的增加，空间依赖性程度显著增加（P < 0.05）。这些结果表明，在小区杀虫剂试验中，行内根系样本之间的最小距离应大于1米，以获得无偏的根系损伤估计值。
