The evolution of pathogen defence in insect hosts: whitefly resistance to biocontrol agents in horticulture

使用常规化学杀虫剂控制农业害虫导致了广泛的抗药性进化，并引发了广泛的生物多样性丧失。为应对这些问题，许多农业部门越来越多地转用生物防治制剂(如病原体和寄生蜂)，作为虫害综合管理办法的一部分。然而，与大量关于化学杀虫剂抗性的研究相比，靶标害虫可能对这些生防剂产生抗药性的可能性受到的关注相对较少。对寄生虫的进化反应通常被认为是由于核基因组编码的免疫系统组件的变化。然而，其他因素往往强烈影响昆虫寄主对感染的敏感性，并可能为抗性进化提供新的途径。例如，行为可能对感染易感性产生重大影响[2]：避免接触寄生虫的昆虫可能处于显著的进化优势。此外，昆虫对寄生的抵抗力往往受到生活在昆虫组织内的母系遗传共生微生物的强烈影响：在许多系统中，这些“有影响力的乘客”可能是感染易感性的主要决定因素，这意味着抵抗力可以通过一种新的共生体的传播而不是通过基因组进化来进化[3]。温室烟粉虱是世界各地的一种主要农业害虫；在英国，它尤其影响温室园艺。它通过吸取汁液、在树叶上沉积蜜露从而促进真菌生长以及通过传播一系列病毒感染来破坏植物。这种昆虫对英国的商业温室番茄种植者来说问题尤其严重；种植者部署了一系列防治烟粉虱的药剂，其中两种是寄生蜂Encarsia Formosa和由昆虫病原真菌球孢白僵菌配制的生物杀虫剂。虽然农业单一栽培可以快速选择害虫的抗性表型，但我们特别感兴趣的是如何通过种植多个植物物种/品种来增强园艺中的生态异质性，以及这是否会阻碍抗性进化。

The control of insect pests in agriculture using conventional chemical insecticides has led to widespread insecticide resistance evolution and triggered extensive biodiversity loss. In response to these problems many agricultural sectors are increasingly switching to biological control agents (such as pathogens and parasitoids) as part of an integrated pest management approach. However, in contrast to the volume of research into chemical insecticide resistance, the possibility that target pests may evolve resistance to these biological control agents has received relatively little attention.Insect populations harbour substantial genetic variation for infection susceptibility, providing strong potential for resistance evolution [1]. Evolutionary responses to parasites are often assumed to be due to changes in components of the immune system coded for by the nuclear genome. However, other factors often strongly influence the susceptibility of insect hosts to infection and may provide novel routes to resistance evolution. For example, behaviour can have major impacts on infection susceptibility [2]: insects that avoid contact with parasites may be at a significant evolutionary advantage. Also, insect resistance to parasitism is often strongly influenced by the presence of maternally inherited symbiotic microbes that live inside the insect's tissues: these "influential passengers" can be the principal determinant of infection susceptibility in many systems, meaning that resistance can evolve through the spread of a novel symbiont rather than via genomic evolution [3].The glasshouse whitefly Trialeurodes vaporariorum is a major pest of agriculture worldwide; in the UK it especially affects greenhouse horticulture. It damages plants by removing resources through sap-sucking, depositing honeydew on foliage thereby promoting fungal growth and by vectoring a range of viral infections. This insect is particularly problematic for commercial greenhouse tomato growers in the UK; growers deploy a range of control agents against whitefly, two of which are the parasitoid wasp Encarsia formosa and biopesticides formulated from the entomopathogenic fungus Beauveria bassiana. Whilst agricultural monocultures can rapidly select for resistance phenotypes in pests, we are especially interested in how ecological heterogeneity can be enhanced in horticulture by planting multiple plant species/varieties and whether this can impede resistance evolution.