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

蚜虫是重要的取食植物汁液的昆虫，通过直接取食和传播植物病毒影响植物生态和作物产量。这些小型软体昆虫是众所周知的农作物害虫，也是玫瑰和郁金香等观赏植物的害虫。蚜虫种群自然受到(i)寄主植物抗性和（ii）蚜虫天敌（包括瓢虫、草蛉、蚜虫和寄生蜂）的控制。随着对自然种群中植物如何应对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害虫控制方法。根据目前的气候预测，虫害爆发可能会增加，导致作物产量下降，并通过增加土地改作农业用途或增加农药的使用，对自然环境产生未来的影响。我们已经证明，寄主植物的“抗蚜”防御可以通过接种大麦植物根来诱导，这可以减少蚜虫的繁殖和寿命，从而减少种群规模。我们最近发现，在微生物接种的植物上，蚜虫被寄生蜂寄生的时间更早、更多。拟寄生蜂在蚜虫宿主体内产卵，卵孵化后，幼虫以蚜虫为食，成年后只留下蚜虫身体的干燥外壳（“蚜虫木乃伊”）。我们假设用防御诱导细菌接种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），而蚜虫以接种的植物为食更容易被寄生（免疫反应减少）。蚜虫还拥有多种细菌内共生体，这些细菌内共生体帮助蚜虫以营养贫乏的植物汁液为食，但它们也能赋予蚜虫对寄生蜂的抵抗力。我们将使用一系列行为学研究结合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了解植物根系微生物群如何对地上相互作用产生强烈影响，并跨越多个营养水平（从土壤细菌到草食性昆虫的寄生蜂）。我们的研究结果将提高对自然生态系统和农业生态系统中蚜虫寄生和食草动物调控的理解，从而制定可持续的害虫管理策略。

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.