Plant domestication has commonly reduced levels of secondary metabolites known to confer resistance against insects. Chili pepper is a special case because the fruits of different varieties have been selected for lower and higher levels of capsaicin, the main compound associated with defence. This may have important consequences for insect herbivores and their natural enemies. Despite the widespread consumption of chili peppers worldwide, the effects of capsaicin on insects are poorly understood. Here, we investigated the effect of capsaicin on a generalist herbivore, Spodoptera latifascia (Lepidoptera: Noctuidae) and its ectoparasitoid, Euplectrus platyhypenae (Hymenoptera: Eulophidae). Using chili varieties with three pungency levels: non-pungent (Padron), mild (Cayenne) and highly pungent (Habanero), as well as artificial diets spiked with three different levels of synthetic capsaicin, we determined whether higher capsaicin levels negatively affect the performance of these insects. Overall, capsaicin had a negative effect on both herbivore and parasitoid performance, particularly at high concentrations. Caterpillars reared on highly pungent fruits and high-capsaicin diet had longer development time, reduced pupation success, lower adult emergence, but also lower parasitism rates than caterpillars reared on mild or non-capsaicin treatments. In addition, we found that the caterpillars were capable of sequestering capsaicinoids in their haemolymph when fed on the high pungent variety with consequences for parasitoids’ performance and oviposition decisions. These results increase our understanding of the role of capsaicin as a chemical defence against insects and its potential implications for pest management.

植物驯化通常会降低已知赋予昆虫抗性的次级代谢物水平。辣椒是一个特例，因为不同品种的果实中辣椒素的含量越来越低，辣椒素是与防御相关的主要化合物。这可能对昆虫食草动物及其天敌产生重要影响。尽管世界范围内广泛食用辣椒，但人们对辣椒素对昆虫的影响却知之甚少。在这里，我们研究了辣椒素对多面食草动物Spodoptera latifascia（鳞翅目：夜蛾科）及其外寄生蜂 Euplectrus platyhypenae 的影响（膜翅目：Eulophidae）。使用具有三种辛辣度的辣椒品种：无辛辣味 (Padron)、轻度辛辣味 (Cayenne) 和高度辛辣味 (Habanero)，以及添加三种不同水平的合成辣椒素的人工饮食，我们确定较高的辣椒素水平是否会对性能产生负面影响这些昆虫。总的来说，辣椒素对食草动物和寄生蜂的表现都有负面影响，特别是在高浓度下。以辛辣水果和高辣椒素饮食饲养的毛虫发育时间较长，化蛹成功率较低，成虫出苗率较低，但寄生率也低于以温和或非辣椒素处理饲养的毛虫。此外，我们发现当以高刺激性品种为食时，毛虫能够在其血淋巴中隔离辣椒素，从而影响寄生蜂的表现和产卵决定。这些结果增加了我们对辣椒素作为化学防御昆虫的作用及其对害虫管理的潜在影响的理解。