Data from: Parasitoid wasps indirectly suppress seed production by stimulating consumption rates of their seed-feeding hosts

1. In parasitoid–herbivore–plant food chains, parasitoids may be simultaneously linked with both herbivore hosts and plants, as occurs when herbivores attacked by parasitoids continue to consume plants although they are destined to die. This peculiar property may cause parasitoids to confer a differential trophic cascading effect on plants than that known for typical predators. 2. We hypothesized that larval koinobiont parasitoids would confer an immediate negative effect on plant seed production by stimulating consumption of their seed-predator hosts. We tested this hypothesis in an alpine parasitic food chain of plant seeds, pre-dispersal seed predators (tephritid fly larvae) and koinobiont parasitoids using field observations, a field experiment and a microcosm study. 3. We first compared observed seed production in (i) non-infected capitula, (ii) capitula infected only by seed predators (tephritid flies) and (iii) capitula infected by both seed predators and their parasitoids in five Asteraceae species. Consistent with our hypothesis, seed loss in the capitula with both seed predators and parasitoids was significantly greater than in the capitula infested only by seed predators. 4. This effect was replicated in a controlled field experiment focusing on the most common parasitoid–seed predator–plant interaction chain in our system, in which confounding factors (e.g. density and phenology) were excluded. Here, we show that parasitoids indirectly decreased plant seed production by changing the behaviour of seed predators. 5. In a microcosm study, we show that larval parasitoids significantly extended the growth period and increased the terminal size of their host tephritid maggots. Thus, parasitoids suppressed plant seed production by stimulating the growth and consumption of the fly maggots. 6. In contrast to the typical predator-induced trophic cascade, we highlight the significance of parasitoids indirectly decreasing plant fitness by stimulating consumption by seed predators. Future studies on trophic interactions should consider the net effect of both increased consumption by seed predators and their death after development of parasitoids.

1. 在寄生蜂（parasitoid）-植食者-植物食物链中，寄生蜂可能同时与植食性寄主和植物产生关联——例如被寄生蜂攻击的植食者即便最终死亡，仍会继续取食植物。这一特殊特性可能使寄生蜂对植物产生与典型捕食者截然不同的营养级联效应。
2. 我们提出假说：幼虫期抑育型寄生蜂（koinobiont parasitoid）可通过刺激其种子捕食者寄主的取食行为，对植物种子产量产生直接负面影响。我们依托由植物种子、扩散前种子捕食者（实蝇幼虫，tephritid fly larvae）和抑育型寄生蜂构成的高山寄生食物链，结合野外观测、野外实验与微宇宙实验对该假说进行了验证。
3. 我们首先在5种菊科（Asteraceae）植物中，对比了三类头状花序的种子产量：（i）未被侵染的头状花序，（ii）仅被种子捕食者（实蝇）侵染的头状花序，以及（iii）同时被种子捕食者及其寄生蜂侵染的头状花序。结果与假说一致：同时存在种子捕食者与寄生蜂的头状花序的种子损失量，显著高于仅被种子捕食者侵染的头状花序。
4. 我们针对研究体系中最常见的寄生蜂-种子捕食者-植物互作食物链开展了控制变量野外实验，排除了密度、物候等混杂因素，成功重复了上述效应。本研究证实，寄生蜂可通过改变种子捕食者的行为，间接降低植物的种子产量。
5. 在微宇宙实验中，我们发现寄生蜂幼虫可显著延长其寄主实蝇幼虫的生长周期，并增大其最终体型。由此可见，寄生蜂通过促进实蝇幼虫的生长与取食，抑制了植物的种子产量。
6. 与典型的捕食者诱导型营养级联效应不同，本研究强调了寄生蜂通过刺激种子捕食者的取食行为，间接降低植物适合度的重要意义。未来针对营养互作的研究，应同时考虑种子捕食者取食增加与寄生蜂发育完成后寄主死亡这两方面的净效应。