Department of Zoology and Entomology, University of Fort Hare, Alice 5700, South Africa.
Department of Biological and Environmental Sciences, Walter Sisulu University, Mthatha 5117, South Africa.
J Econ Entomol. 2023 Oct 10;116(5):1551-1559. doi: 10.1093/jee/toad156.
The diamondback moth (Plutella xylostella L.) is the most destructive insect pest on cabbage (Brassica oleracea var. capitata L.). Infestation by this pest usually results in the indiscriminate use of insecticides by farmers due to a lack of sampling plans for this pest. Sampling plans for P. xylostella management decisions on winter-spring cabbage in the Eastern Cape Province of South Africa were developed, through population monitoring that comprised weekly counts of immature stages of P. xylostella on 60 plants for 11 wk each during the winter and spring seasons. The mean density-variance relationship was used to describe the distribution of the pest, and number of infested plants was used to develop a fixed-precision sampling plan. All plant growth stages preceding maturation were vulnerable to P. xylostella damage resulting in yield losses. A high aggregation of P. xylostella on cabbage was observed in spring than in winter. The average sample number to estimate P. xylostella density within a 15% standard error of the mean was 35 plants. Furthermore, the estimated plant proportion action threshold (AT) was 51% with density action thresholds of 0.50 and 0.80 for spring and winter, respectively. Fitting P. xylostella cumulative counts in the winter and spring sampling plans resulted in 100% and 45% reduction in insecticide treatments. The similarity of sample size and ATs between both seasons provides evidence that a single sampling plan is practical for all cabbage growing seasons. The similarity of the estimated ATs to those acceptable in established integrated pest management programs indicates reliability.
小菜蛾（Plutella xylostella L.）是十字花科白菜（Brassica oleracea var. capitata L.）上最具破坏性的害虫。由于缺乏这种害虫的抽样计划，农民通常会因这种害虫的侵袭而不加选择地使用杀虫剂。本研究通过对冬季和春季每 11 周每周对 60 株植物上未成熟的小菜蛾进行计数，制定了南非东开普省冬季-春季白菜小菜蛾管理决策的抽样计划。使用平均密度-方差关系来描述害虫的分布，并使用受虫害植物的数量来制定固定精度抽样计划。在成熟之前的所有植物生长阶段都容易受到小菜蛾的伤害，导致产量损失。在春季观察到小菜蛾在白菜上的聚集程度高于冬季。估计小菜蛾密度的平均样本数为 35 株，可以将平均值的 15%标准误差内的密度估计值。此外，估计的植物比例行动阈值（AT）为 51%，春季和冬季的密度行动阈值分别为 0.50 和 0.80。在冬季和春季抽样计划中拟合小菜蛾的累积计数，可使杀虫剂处理减少 100%和 45%。两个季节的样本量和 ATs 的相似性为所有白菜种植季节使用单一抽样计划提供了证据。估计的 ATs 与既定综合虫害管理计划中可接受的 ATs 相似，表明其可靠性。
