Pokharel Prayan, Sippel Marlon, Vilcinskas Andreas, Petschenka Georg
Institute of Phytomedicine, University of Hohenheim, 70599 Stuttgart, Germany.
Institute for Insect Biotechnology, Justus Liebig University Giessen, 35392 Giessen, Germany.
Insects. 2020 Jul 31;11(8):485. doi: 10.3390/insects11080485.
Predators and parasitoids regulate insect populations and select defense mechanisms such as the sequestration of plant toxins. Sequestration is common among herbivorous insects, yet how the structural variation of plant toxins affects defenses against predators remains largely unknown. The palearctic milkweed bug (Heteroptera: Lygaeinae) was recently shown to sequester cardenolides from (Ranunculaceae), while its relative also obtains cardenolides but from (Plantaginaceae). Remarkably, toxin sequestration protects both species against insectivorous birds, but only gains protection against predatory lacewing larvae. Here, we used a full factorial design to test whether this difference was mediated by the differences in plant chemistry or by the insect species. We raised both species of milkweed bugs on seeds from both species of host plants and carried out predation assays using the larvae of the lacewing . In addition, we analyzed the toxins sequestered by the bugs via liquid chromatography (HPLC). We found that both insect species gained protection by sequestering cardenolides from but not from . Since the total amount of toxins stored was not different between the plant species in and even lower in from compared to , the effect is most likely mediated by structural differences of the sequestered toxins. Our findings indicate that predator-prey interactions are highly context-specific and that the host plant choice can affect the levels of protection to various predator types based on structural differences within the same class of chemical compounds.
捕食者和寄生蜂会调节昆虫种群数量，并促使昆虫形成诸如储存植物毒素等防御机制。储存毒素在食草昆虫中很常见，但植物毒素的结构变化如何影响对捕食者的防御作用，在很大程度上仍不清楚。最近有研究表明，古北区的乳草蝽（半翅目：长蝽亚科）会从毛茛科植物中储存强心苷，而与之亲缘关系较近的另一种乳草蝽也能获取强心苷，但来源是车前科植物。值得注意的是，毒素储存能保护这两个物种免受食虫鸟类的侵害，但只有一种乳草蝽能抵御捕食性草蛉幼虫。在此，我们采用全因子设计来测试这种差异是由植物化学组成的差异还是昆虫种类的差异所介导的。我们用两种寄主植物的种子饲养这两种乳草蝽，并使用草蛉幼虫进行捕食试验。此外，我们通过液相色谱法（HPLC）分析了乳草蝽储存的毒素。我们发现，这两种昆虫通过从一种植物中储存强心苷而获得保护，但从另一种植物中储存则不能。由于在一种植物中储存的毒素总量在两种植物间并无差异，而在另一种植物中储存的毒素总量甚至比前一种植物更低，所以这种效应很可能是由所储存毒素的结构差异介导的。我们的研究结果表明，捕食者与猎物之间的相互作用具有高度的情境特异性，寄主植物的选择会基于同一类化合物内部的结构差异，影响对不同类型捕食者的保护水平。
