Herbivore-induced plant volatiles (HIPVs) provide direct benefits to plants as antimicrobials and herbivore repellents, but their potential as direct toxins to herbivores is unclear. Here, we assayed the larvicidal activity of six common HIPVs from three different biochemical pathways and tested the hypothesis that the larvicidal activity of HIPVs is related to the host specialization of the insect pest. We first assessed β-caryophyllene, linalool, z-3-hexenyl acetate, z-3-hexenol, e-2-hexenal, and indole against the beet armyworm (Spodoptera exigua) and found that indole was sevenfold more toxic compared to the other volatiles when incorporated into the diet. Then, we tested the larvicidal activity of indole against six common, destructive pest caterpillars with varying host ranges. Consistent with our hypothesis, indole toxicity varied with caterpillar host range: indole toxicity was sevenfold higher in more specialized insect species relative to generalist insect species. That said, the LC₅₀ of indole was comparable to other reported anti-herbivore agents even against the generalist caterpillars. Yet, indole in headspace had neither larvicidal nor ovicidal activity on any caterpillar species tested. These results support a key ecological precept of a trade-off between host specialization and chemical detoxification and also indicate that indole in particular is directly toxic to herbivores and therefore potentially useful in integrated pest management strategies.

中文翻译：

---

植物挥发性吲哚的急性毒性取决于草食动物的专业性

草食动物诱导的植物挥发物（HIPV）作为抗微生物剂和草食动物驱避剂为植物提供了直接的好处，但是它们作为草食动物的直接毒素的潜力尚不清楚。在这里，我们分析了来自三种不同生化途径的六个常见HIPV的杀幼虫活性，并检验了HIPV的杀幼虫活性与害虫宿主特化有关的假说。我们首先评估了β-石竹烯，芳樟醇，z -3-己烯基乙酸酯，z -3-己烯醇，e -2-己烯醛和吲哚对甜菜夜蛾（Spodoptera exigua）），并发现与饮食中的其他挥发物相比，吲哚的毒性要高7倍。然后，我们测试了吲哚对六种具有不同寄主范围的常见，破坏性虫害毛虫的杀幼虫活性。与我们的假设一致，吲哚的毒性随毛虫寄主范围的不同而变化：相对于普通昆虫，较专门的昆虫种类的吲哚毒性高7倍。也就是说，LC ₅₀吲哚的抗性甚至可以对抗多毛虫，也可以与其他报道的抗草食动物药媲美。然而，顶空的吲哚对所测试的任何毛虫物种均没有杀幼虫或杀卵活性。这些结果支持了宿主专门化和化学解毒之间折衷的关键生态学原理，并且还表明，尤其是吲哚对草食动物有直接毒性，因此可能在有害生物综合治理策略中有用。