Temperate Tree Fruit and Vegetable Research Unit, USDA-ARS, Wapato, WA.
US Vegetable Lab, USDA-ARS, Charleston, SC.
J Econ Entomol. 2021 Apr 13;114(2):818-827. doi: 10.1093/jee/toaa320.
Twospotted spider mite, Tetranychus urticae Koch (Trombidiformes: Tetranychidae), is an important, worldwide pest of watermelon, Citrullus lanatus L. (Thunb.) Matsum. & Nakai (Cucurbitales: Cucurbitaceae). Feeding results in chlorotic spots and leaf necrosis, which can substantially reduce yields. In watermelon, T. urticae is managed solely with acaricides. Issues with acaricide resistance and pesticide label restrictions on number of applications per season require research-based recommendations on products with effective, long-lasting residues. To improve recommendations for T. urticae management in watermelon and to measure possible effects on non-target beneficial mites, we conducted acaricide efficacy trials in two locations in South Carolina, United States. The adulticidal products abamectin, bifenazate, fenpyroximate, and tolfenpyrad and the ovicidal products spiromesifen and etoxazole were tested. We also conducted two bioassays to better determine duration of acaricide residues. In the field trials, all acaricides except tolfenpyrad reduced T. urticae abundance, but all acaricides also reduced abundance of the most common predatory mite, Neoseiulus fallacis (Garman) (Mesostigmata: Phytoseiidae). In the bioassays, abamectin and bifenazate residues caused high adult T. urticae mortality at up to 21 d after treatment, performing better than fenpyroximate and tolfenpyrad. Etoxazole and spiromesifen were longer lasting, with <1 offspring per treated female in the etoxazole treatment at 28 d after treatment. Based on efficacy, abamectin or bifenazate should be rotated with etoxazole for fast knockdown of active stages while reducing reproduction, respectively. However, development and registration of more selective acaricides in watermelon is needed to preserve biological control of T. urticae by predatory mites.
二斑叶螨，Tetranychus urticae Koch（蜱螨目：叶螨科），是一种重要的、全球性的西瓜害虫，Citrullus lanatus L.（葫芦目：葫芦科）。其取食会导致叶片出现褪绿斑点和坏死，从而大幅降低产量。在西瓜上，二斑叶螨完全依靠杀螨剂来防治。杀螨剂抗性问题以及每个季节应用次数的标签限制，都要求我们基于研究，推荐具有有效且持久残留的产品。为了改进西瓜中二斑叶螨防治的建议，并衡量其对非靶标有益螨的可能影响，我们在美国南卡罗来纳州的两个地点进行了杀螨剂药效试验。测试了杀成虫药剂阿维菌素、丁氟螨酯、唑螨酯和唑吡萘菌胺，以及杀卵药剂螺螨酯和乙唑螨腈。我们还进行了两项生物测定，以更好地确定杀螨剂残留的持续时间。在田间试验中，除了唑吡萘菌胺外，所有杀螨剂都降低了二斑叶螨的种群密度，但所有杀螨剂也降低了最常见捕食性螨类，Neoseiulus fallacis（Garman）（中气门目：植绥螨科）的种群密度。在生物测定中，阿维菌素和丁氟螨酯处理后 21 天内，仍能导致成螨二斑叶螨的高死亡率，表现优于唑螨酯和唑吡萘菌胺。乙唑螨腈和螺螨酯的持效期更长，处理后 28 天，乙唑螨腈处理中每只处理雌螨的后代数<1。基于药效，阿维菌素或丁氟螨酯应与乙唑螨腈轮用，以快速击倒活动态螨，同时降低其繁殖能力。然而，需要开发和登记更多在西瓜中具有选择性的杀螨剂，以保护捕食性螨类对二斑叶螨的生物防治作用。
