Pyrrolizidine alkaloids (PAs) are the major defense compounds of plants in the Senecio genus. Here I will review the effects of PAs in Senecio on the preference and performance of specialist and generalist insect herbivores. Specialist herbivores have evolved adaptation to PAs in their host plant. They can use the alkaloids as cue to find their host plant and often they sequester PAs for their own defense against predators. Generalists, on the other hand, can be deterred by PAs. PAs can also affect survival of generalist herbivores. Usually generalist insects avoid feeding on young Senecio leaves, which contain a high concentration of alkaloids. Structurally related PAs can differ in their effects on insect herbivores, some are more toxic than others. The differences in effects of PAs on specialist and generalists could lead to opposing selection on PAs, which may maintain the genetic diversity in PA concentration and composition in Senecio species.

中文翻译：

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吸引和威慑：吡咯里西啶生物碱在植物-昆虫相互作用中的双重作用。

吡咯里西啶生物碱（PAs）是千里光属植物的主要防御化合物。在这里，我将回顾千里光中 PA 对专业和通才昆虫食草动物的偏好和表现的影响。专业食草动物已经进化出对寄主植物中 PA 的适应性。他们可以使用生物碱作为寻找寄主植物的线索，而且他们通常会隔离 PA 以抵御捕食者。另一方面，通才可能会被 PA 吓倒。PA 还可以影响多面食草动物的生存。通常通才昆虫会避免以含有高浓度生物碱的千里光幼叶为食。结构相关的 PA 对昆虫食草动物的影响可能不同，有些比其他的毒性更大。