Impact of plant-beneficial soil microbes on aboveground parasitism of insect herbivores

蚜虫是一种重要的食汁性昆虫，通过直接取食和传播植物病毒来影响植物生态和作物产量。这些软体小昆虫是众所周知的农作物害虫，也是玫瑰、郁金香等观赏植物。(1)寄主植物抗性和(2)蚜虫天敌(包括瓢虫、草莓、食蚜虫和寄生蜂)自然控制着蚜虫的种群数量。随着对植物如何应对自然种群中食草动物的深入了解，我们可以利用这些有益的相互作用，并实施可持续的虫害控制方法。在目前的气候预测下，虫害暴发可能会增加，导致作物减产，并通过增加退耕还林或增加使用杀虫剂来影响未来的自然环境。我们已经证明，通过向大麦植物的根部接种自然产生的有益细菌，可以诱导寄主植物的抗蚜虫防御，从而减少蚜虫的繁殖和寿命，从而减少种群规模。我们最近发现，在接种微生物的植物上，蜜蜂被寄生蜂寄生的时间更早、更多。寄生蜂在蚜虫寄主体内产卵，卵孵化后，幼虫以蚜虫为食，成虫羽化后只留下蚜虫身体的一层干壳(“蚜虫木乃伊”)。我们假设，接种防御诱导细菌的植物增加了植物对寄生蜂的吸引力(通过植物挥发性化学物质)，而以接种的植物为食的蚜虫更容易受到寄生(免疫反应降低)。蚜虫还寄生着各种细菌内共生体，帮助蚜虫以营养不良的植物汁液为食，但它们也可以对寄生蜂产生抵抗力。我们将使用一套行为研究结合对植物和蚜虫的化学分析来了解植物接种有益细菌如何导致蚜虫寄生增加。这项工作将有助于我们理解植物根部微生物如何对地上相互作用产生强烈影响，并跨越多个营养水平(从土壤细菌到草食昆虫的寄生蜂)。我们的结果将提高对(I)自然生态系统和(Ii)农业生态系统中的蚜虫寄生和食草动物调控的理解，使可持续虫害管理战略的发展成为可能。

Aphids are important plant sap-feeding insects, affecting plant ecology and crop yields by direct feeding and transmission of plant viruses. These small soft-bodied insects are well-known pests of agricultural crops, as well as ornamental plants such as roses and tulips. Populations of aphids are naturally controlled by (i) host plant resistance and (ii) aphid natural enemies (including ladybirds, lacewings, syrphids, and parasitoid wasps). With a deeper understanding of how plants deal with herbivores in natural populations, we can exploit these beneficial interactions and implement sustainable pest control methods. Under current climate predictions, insect pest outbreaks are likely to increase with consequences for reduced crop yields and future impacts on the natural environment through increased conversion of land for agriculture or increased application of pesticides.We have shown that host plant 'anti-aphid' defences can be induced by inoculating barley plant roots with naturally occurring beneficial bacteria, which reduces aphid reproduction and lifespan, and thus population sizes. We recently discovered that aphids on microbe-inoculated plants are parasitized more and earlier by parasitoid wasps. Parasitoid wasps lay an egg inside the aphid host and, after egg-hatching, the larva feeds on the aphid before emerging as an adult leaving only a dry husk of the aphid body behind (an 'aphid mummy'). We hypothesise that plant inoculation with defence-inducing bacteria increases the attractiveness of plants to parasitoid wasps (via plant volatile chemicals), and that aphids feeding on inoculated plants are more susceptible to parasitism (reduced immune responses). Aphids also host a variety of bacterial endosymbionts that help aphids to feed on nutritionally poor plant sap, but they can also confer resistance to parasitoid wasps. We will use a set of behavioural studies combined with chemical analysis of the plant and aphid to understand how plant inoculation with beneficial bacteria can lead to increased parasitism of aphids.This work will contribute to our understanding of how plant root microbiomes can have strong impacts on aboveground interactions, and across multiple trophic levels (from soil bacteria to parasitoid wasps of herbivorous insects). Our results will improve understanding of aphid parasitism and herbivore regulation in both (i) natural ecosystems, and (ii) agroecosystems, enabling the development of sustainable insect pest management strategies.