Bioinsecticides based on Bacillus thuringiensis toxins can be a safe alternative to chemical pesticides currently used to control Spodoptera exigua (Hübner; Lepidoptera: Noctuidae)–a worldwide, polyphagous pest species. However, only a few B. thuringiensis proteins have been proven effective against S. exigua and currently used B. thuringiensis bioinsecticides are not efficient in control of this pest–therefore, new biocontrol approaches are needed. Some research suggest that synergistic interactions can occur between certain Bt toxins and increase their insecticidal activity. Multiple-toxin bioinsecticides are also recommended to prevent field-evolved resistance. In this study, the insecticidal efficacy of five selected B. thuringiensis proteins (Cry1Aa, Cry1Ca, Cry1Ia, Cry2Ab and Vip3Aa) has been assessed, together with eight mixtures containing two or three of these toxins. The composition containing Cry1Ca and Vip3Aa is the most active against S. exigua, followed by: Cry1Aa + Vip3Aa; Cry2Ab + Vip3Aa; Cry1Aa + Cry2Ab + Vip3Aa; Cry1Aa + Cry1Ca; Cry1Ca + Cry2Ab and Cry1Aa + Cry1Ca + Cry2Ab. The results gathered at 7 days after treatment (DAT) indicate synergistic interactions between most of these mixtures. Interestingly, the results obtained at 10 DAT suggest synergism only in three combinations (Cry1Ca + Vip3Aa, Cry1Aa + Vip3Aa, Cry1Aa + Cry1Ca). Moreover, the estimated synergism factors are 1.6-2.2-fold lower than at 7 DAT. The only exception is the Cry1Ca + Vip3Aa composition, for which high synergism factor (>4) was calculated at both scoring times. This work shows that the time of data record can substantially influence the interaction type estimation. The most potent compositions should be used to develop new bioinsecticides (transgenic crops or targeted recombinant strains) with high effectiveness against S. exigua.

中文翻译：

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苏云金芽孢杆菌控制中苏云金芽孢杆菌Cry1，Cry2和Vip3毒素组合的杀虫活性：协同作用和数据评分的重点

以苏云金芽孢杆菌毒素为基础的生物杀虫剂可以安全替代目前用于防治全球范围内多食性害虫种类的斜纹夜蛾（Hübner；鳞翅目：夜蛾科）的化学农药。然而，只有少量的苏云金芽孢杆菌蛋白被证明对艾门链球菌有效，而目前使用的苏云金芽孢杆菌生物杀虫剂不能有效控制这种害虫，因此，需要新的生物防治方法。一些研究表明，某些Bt毒素之间可能发生协同相互作用，并增加其杀虫活性。还建议使用多种毒素的生物杀虫剂，以防止田间发展的抗药性。在这项研究中，评估了5种选定的苏云金芽孢杆菌蛋白（Cry1Aa，Cry1Ca，Cry1Ia，Cry2Ab和Vip3Aa）的杀虫功效，以及含有两种或三种这些毒素的八种混合物。包含Cry1Ca和Vip3Aa的组合物对S. exigua具有最强的活性，其后为：Cry1Aa + Vip3Aa；Cry2Ab + Vip3Aa; Cry1Aa + Cry2Ab + Vip3Aa; Cry1Aa + Cry1Ca; Cry1Ca + Cry2Ab和Cry1Aa + Cry1Ca + Cry2Ab。处理后第7天（DAT）收集的结果表明，大多数混合物之间存在协同作用。有趣的是，在10 DAT时获得的结果表明仅在三种组合（Cry1Ca + Vip3Aa，Cry1Aa + Vip3Aa，Cry1Aa + Cry1Ca）中具有协同作用。此外，估计的协同因子比7天DAT低1.6-2.2倍。唯一的例外是Cry1Ca + Vip3Aa组合物，在两个计分时间均计算出高协同因子（> 4）。这项工作表明，数据记录的时间会大大影响交互类型的估计。最有效的组合物应被用于开发具有新的生物杀虫剂（转基因作物或针对性的重组菌株），并且具有高效的抗S. exigua的能力。