Twospotted spider mite (Tetranychus urticae Koch) is a cosmopolitan pest of numerous plants, including hop (Humulus lupulus L.). The most costly damage from the pest on hop results from infestation of cones, which are the harvested product, which can render crops unsalable if cones become discolored. We analyzed 14 yr of historical data from 312 individual experimental plots in western Oregon to identify risk factors associated with visual damage to hop cones from T. urticae. Logistic regression models were fit to estimate the probability of cone damage. The most predictive model was based on T. urticae-days during mid-July to harvest, which correctly predicted occurrence and nonoccurrence of cone damage in 91 and 93% of data sets, respectively, based on Youden’s index. A second model based on the ratio of T. urticae to predatory arthropods late in the season correctly predicted cone damage in 92% of data sets and nonoccurrence of damage in 77% of data sets. The model based on T. urticae abundance performed similarly when validated in 23 commercial hop yards, whereas the model based on the predator:prey ratio was relatively conservative and yielded false-positive predictions in 11 of the 23 yards. Antecedents of these risk factors were explored and quantified by structural equation modeling. A simple path diagram was constructed that conceptualizes T. urticae invasion of hop cones as dependent on prior density of the pest on leaves in early spring and summer, which in turn influences the development of predatory arthropods that mediate late-season density of the pest. In summary, the biological insights and models developed here provide guidance to pest managers on the likelihood of visual cone damage from T. urticae that can inform late-season management based on both abundance of the pest and its important predators. This is critically important because a formal economic threshold for T. urticae on hop does not exist and current management efforts may be mistimed to influence the pest when crop damage is most probable. More broadly, this research suggests that current management practices that target T. urticae early in the season may in fact predispose yards to later outbreaks of the pest.

中文翻译：

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预测叶螨对啤酒花球果的损害（螨：叶螨科）

双斑叶螨 (Tetranychus urticae Koch) 是包括啤酒花 (Humulus lupulus L.) 在内的多种植物的世界性害虫。啤酒花上害虫造成的最昂贵的损失是由于锥体的侵染，锥体是收获的产品，如果锥体变色，这会使作物无法销售。我们分析了俄勒冈州西部 312 个独立试验区 14 年的历史数据，以确定与荨麻疹球果视觉损伤相关的风险因素。逻辑回归模型适合估计锥体损坏的概率。最具预测性的模型是基于 7 月中旬收获的荨麻疹天数，根据约登指数，该模型分别正确预测了 91% 和 93% 的数据集中锥体损伤的发生和未发生。基于 T 比率的第二个模型。本赛季后期捕食性节肢动物的荨麻疹在 92% 的数据集中正确预测了锥体损伤，在 77% 的数据集中未发生损伤。基于 T. urticae 丰度的模型在 23 个商业啤酒花码中验证时表现相似，而基于捕食者：猎物比率的模型相对保守，并在 23 个码中的 11 个产生假阳性预测。通过结构方程模型探索和量化了这些风险因素的前因。构建了一个简单的路径图，将 T. urticae 对啤酒花球果的入侵概念化为依赖于早春和夏季叶片上害虫的先前密度，这反过来又影响了调节晚季害虫密度的捕食性节肢动物的发育。总之，这里开发的生物学见解和模型为害虫管理人员提供了关于 T. urticae 视锥损伤可能性的指导，可以根据害虫及其重要捕食者的丰度为后期管理提供信息。这一点非常重要，因为不存在啤酒花上荨麻疹的正式经济阈值，并且当前的管理工作可能不合时宜，无法在作物最有可能受到损害时影响害虫。更广泛地说，这项研究表明，当前针对 T. urticae 在季节早期的管理实践实际上可能使院子容易在以后爆发害虫。这一点非常重要，因为不存在啤酒花上荨麻疹的正式经济阈值，并且当前的管理工作可能不合时宜，无法在作物最有可能受到损害时影响害虫。更广泛地说，这项研究表明，当前针对 T. urticae 在季节早期的管理实践实际上可能使院子容易在以后爆发害虫。这一点非常重要，因为不存在啤酒花上荨麻疹的正式经济阈值，并且当前的管理工作可能不合时宜，无法在作物最有可能受到损害时影响害虫。更广泛地说，这项研究表明，当前针对 T. urticae 在季节早期的管理实践实际上可能使院子容易在以后爆发害虫。