Plant-mediated interactions are an important force in insect ecology. Through such interactions, herbivores feeding on leaves can affect root feeders. However, the mechanisms regulating the effects of above-ground herbivory on below-ground herbivores are poorly understood. Here, we investigated the performance of cabbage root fly larvae (Delia radicum) on cabbage plants (Brassica oleracea) previously exposed to above ground herbivores belonging to two feeding guilds: leaf chewing diamondback moth caterpillars (Plutella xylostella) or phloem-feeding cabbage aphids (Brevicoryne brassicae). Our study focusses on root-herbivore performance and defence signalling in primary roots by quantifying phytohormones and gene expression. We show that leaf herbivory by caterpillars, but not by aphids, strongly attenuates root herbivore performance. Above-ground herbivory causes changes in primary roots in terms of gene transcripts and metabolites involved in plant defence. Feeding by below-ground herbivores strongly induces the jasmonate pathway in primary roots. Caterpillars feeding on leaves cause a slight induction of the primary root jasmonate pathway and interact with plant defence signalling in response to root herbivores. In conclusion, feeding by a leaf chewer and a phloem feeder differentially affects root-herbivore performance, root-herbivore-induced phytohormonal signalling, and secondary metabolites.

中文翻译：

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毛毛虫和蚜虫的叶食草对根部的植物激素信号传导和植物对根部食草动物的防御产生不同的影响。


植物介导的相互作用是昆虫生态学的重要力量。通过这种相互作用，以叶子为食的食草动物可以影响以根为食的动物。然而，人们对调节地上食草动物对地下食草动物影响的机制知之甚少。在这里，我们研究了甘蓝根蝇幼虫（Delia radicum）在甘蓝植物（Brassica oleracea）上的表现，这些甘蓝植物先前暴露于属于两个取食行会的地上食草动物：咀嚼小菜蛾毛虫（Plutella xylostella）或食韧皮部的甘蓝蚜虫（Plutella xylostella）。短甘蓝）。我们的研究重点是通过量化植物激素和基因表达来研究根食草动物的性能和初生根的防御信号。我们发现，毛毛虫（而非蚜虫）对叶的食草会强烈削弱根食草动物的性能。地上食草动物会导致初生根在涉及植物防御的基因转录本和代谢物方面发生变化。地下食草动物的取食强烈诱导初生根中的茉莉酸途径。以叶子为食的毛毛虫会轻微诱导初生根茉莉酸途径，并与响应根食草动物的植物防御信号相互作用。总之，咀嚼食者和韧皮部食者的取食对根食草动物的性能、根食草动物诱导的植物激素信号传导和次级代谢产物有不同的影响。