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

传统化学杀虫剂对农业害虫的控制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。针对这些问题，许多农业部门越来越多地转向生物防治剂（如病原体和拟寄生虫），作为综合虫害管理方法的一部分。然而，与对化学杀虫剂抗性的大量研究相比，目标害虫可能进化出对这些生物防治剂的抗性的可能性得到的关注相对较少。昆虫种群具有大量的感染易感性遗传变异，这为抗性进化提供了强大的潜力。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成分的变化。然而，其他因素往往强烈影响昆虫宿主对感染的易感性，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：避免与寄生虫接触的昆虫可能具有显著的进化优势。此外，昆虫对寄生的抵抗力通常受到寄生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新共生体的传播而不是通过基因组进化来进化[10]。温室粉虱是世界范围内的主要农业害虫；在英国，它尤其影响温室园艺。它通过吸取汁液、在叶子上沉积蜜露从而促进真菌生长以及通过媒介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尤其成问题；种植者使用一系列防治粉虱的药剂，其中两种是拟寄生蜂台湾白蝇和由昆虫病原真菌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种植物物种/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.