Hamilton A J, Waters E K, Kim H J, Pak W S, Furlong M J
Department of Resource Management and Geography, Melbourne School of Land and Food Resources, The University of Melbourne, 500 Yarra Blvd., Richmond, Victoria 3121, Australia.
J Econ Entomol. 2009 Jun;102(3):1336-43. doi: 10.1603/029.102.0361.
The combined action of two lepidoteran pests, Plutella xylostella L. (Plutellidae) and Pieris rapae L. (Pieridae),causes significant yield losses in cabbage (Brassica oleracea variety capitata) crops in the Democratic People's Republic of Korea. Integrated pest management (IPM) strategies for these cropping systems are in their infancy, and sampling plans have not yet been developed. We used statistical resampling to assess the performance of fixed sample size plans (ranging from 10 to 50 plants). First, the precision (D = SE/mean) of the plans in estimating the population mean was assessed. There was substantial variation in achieved D for all sample sizes, and sample sizes of at least 20 and 45 plants were required to achieve the acceptable precision level of D < or = 0.3 at least 50 and 75% of the time, respectively. Second, the performance of the plans in classifying the population density relative to an economic threshold (ET) was assessed. To account for the different damage potentials of the two species the ETs were defined in terms of standard insects (SIs), where 1 SI = 1 P. rapae = 5 P. xylostella larvae. The plans were implemented using different economic thresholds (ETs) for the three growth stages of the crop: precupping (1 SI/plant), cupping (0.5 SI/plant), and heading (4 SI/plant). Improvement in the classification certainty with increasing sample sizes could be seen through the increasing steepness of operating characteristic curves. Rather than prescribe a particular plan, we suggest that the results of these analyses be used to inform practitioners of the relative merits of the different sample sizes.
小菜蛾（菜蛾科）和菜粉蝶（粉蝶科）这两种鳞翅目害虫的共同作用，给朝鲜的甘蓝（甘蓝变种结球甘蓝）作物造成了严重的产量损失。针对这些种植系统的综合虫害管理（IPM）策略尚处于起步阶段，抽样计划尚未制定。我们使用统计重抽样来评估固定样本量计划（样本量从10株到50株不等）的性能。首先，评估了这些计划在估计总体均值时的精度（D = 标准误/均值）。对于所有样本量，实际得到的D值存在很大差异，分别需要至少20株和45株的样本量，才能至少在50%和75%的时间内达到可接受的精度水平D≤0.3。其次，评估了这些计划在将种群密度相对于经济阈值（ET）进行分类时的性能。为了考虑这两种害虫不同的潜在危害，经济阈值是根据标准昆虫（SI）来定义的，其中1 SI = 1只菜粉蝶 = 5只小菜蛾幼虫。针对作物的三个生长阶段（前期结球、结球期、包心期），使用不同的经济阈值（ET）来实施这些计划：前期结球（1 SI/株）、结球期（0.5 SI/株）和包心期（4 SI/株）。通过操作特征曲线斜率的增加，可以看出随着样本量的增加，分类确定性得到了提高。我们建议不要规定某个特定的计划，而是将这些分析结果用于告知从业者不同样本量的相对优点。
