Tritrophic interactions among plants, herbivorous insects and their parasitoids have been well studied in the past four decades. Recently, a new angle has been uncovered: koinobiont parasitoids, that allow their host to keep feeding on the plant for a certain amount of time after parasitism, indirectly alter plant responses against herbivory via the many physiological changes induced in their herbivorous hosts. By affecting plant responses, parasitoids may indirectly affect the whole community of insects interacting with plants induced by parasitized herbivores and have extended effects on plant fitness. These important findings have renewed research interests on parasitoid manipulation of their host development. Parasitoids typically arrest their host development before the last instar, resulting in a lower final weight compared to unparasitized hosts. Yet, some parasitoids prolong their host development, leading to larger herbivores that consume more plant material than unparasitized ones. Furthermore, parasitoid host regulation is plastic and one parasitoid species may arrest or promote its host growth depending on the number of eggs laid, host developmental stage and species as well as environmental conditions. The consequences of plasticity in parasitoid host regulation for plant–insect interactions have received very little attention over the last two decades, particularly concerning parasitoids that promote their host growth. In this review, we first synthesize the mechanisms used by parasitoids to regulate host growth and food consumption. Then, we identify the evolutionary and environmental factors that influence the direction of parasitoid host regulation in terms of arrestment or promotion of host growth. In addition, we discuss the implication of different host regulation types for the parasitoid’s role as agent of plant indirect defence. Finally, we argue that the recent research interests about parasitoid plant-mediated interactions would strongly benefit from revival of research on the mechanisms, ecology and evolution of host regulation in parasitoids.

在过去的四年里，植物、食草昆虫及其寄生蜂之间的三养相互作用得到了很好的研究。最近，人们发现了一个新的角度：koinobiont 寄生蜂，它允许它们的宿主在寄生后继续以植物为食一段时间，通过在它们的食草宿主中诱导的许多生理变化间接改变植物对食草动物的反应。通过影响植物的反应，寄生蜂可能间接影响整个昆虫群落，这些昆虫与寄生食草动物诱导的植物相互作用，并对植物的适应性产生广泛的影响。这些重要发现重新激发了寄生蜂操纵宿主发育的研究兴趣。寄生蜂通常会在最后一龄之前阻止它们的宿主发育，与未寄生的宿主相比，最终重量较低。然而，一些寄生蜂延长了它们的宿主发育，导致更大的食草动物比未寄生的动物消耗更多的植物材料。此外，寄生蜂的宿主调节是可塑性的，一种寄生蜂物种可能会根据产卵数量、宿主发育阶段和物种以及环境条件来阻止或促进其宿主生长。在过去的二十年里，寄生蜂宿主调控植物-昆虫相互作用的可塑性后果很少受到关注，特别是关于促进宿主生长的寄生蜂。在这篇综述中，我们首先综合了寄生蜂用于调节宿主生长和食物消耗的机制。然后，我们确定了在阻止或促进宿主生长方面影响寄生蜂宿主调控方向的进化和环境因素。此外，我们讨论了不同宿主调节类型对寄生蜂作为植物间接防御剂的作用的影响。最后，我们认为，最近关于寄生蜂植物介导的相互作用的研究兴趣将极大地受益于寄生蜂宿主调控机制、生态学和进化研究的复兴。