Raman A, Wheatley W, Popay A
Charles Sturt University & E H Graham Centre for Agricultural Innovation, Orange, New South Wales 2800, Australia.
Environ Entomol. 2012 Jun;41(3):433-47. doi: 10.1603/EN11317.
Insect association with fungi has a long history. Theories dealing with the evolution of insect herbivory indicate that insects used microbes including fungi as their principal food materials before flowering plants evolved. Subtlety and the level of intricacy in the interactions between insects and fungi indicate symbiosis as the predominant ecological pattern. The nature of the symbiotic interaction that occurs between two organisms (the insect and the fungus), may be either mutualistic or parasitic, or between these two extremes. However, the triangular relationship involving three organisms, viz., an insect, a fungus, and a vascular plant is a relationship that is more complicated than what can be described as either mutualism or parasitism, and may represent facets of both. Recent research has revealed such a complex relationship in the vertically transmitted type-I endophytes living within agriculturally important grasses and the pestiferous insects that attack them. The intricacy of the association depends on the endophytic fungus-grass association and the insect present. Secondary compounds produced in the endophytic fungus-grass association can provide grasses with resistance to herbivores resulting in mutualistic relationship between the fungus and the plant that has negative consequences for herbivorous insects. The horizontally transmitted nongrass type-II endophytes are far less well studied and as such their ecological roles are not fully understood. This forum article explores the intricacy of dependence in such complex triangular relationships drawing from well-established examples from the fungi that live as endophytes in vascular plants and how they impact on the biology and evolution of free-living as well as concealed (e.g., gall-inducing, gall-inhabiting) insects. Recent developments with the inoculation of strains of type-I fungal endophytes into grasses and their commercialization are discussed, along with the possible roles the endophytic fungi play in the galls induced by the Cecidomyiidae (Diptera).
昆虫与真菌的关联有着悠久的历史。关于昆虫食草行为进化的理论表明，在开花植物进化之前，昆虫将包括真菌在内的微生物作为主要食物来源。昆虫与真菌之间相互作用的微妙性和复杂性表明共生是主要的生态模式。两种生物（昆虫和真菌）之间发生的共生相互作用的性质可能是互利共生、寄生，或者介于这两种极端情况之间。然而，涉及昆虫、真菌和维管植物这三种生物的三角关系比互利共生或寄生关系更为复杂，可能兼具两者的特点。最近的研究揭示了在重要农作物禾本科植物体内垂直传播的I型内生真菌与攻击它们的害虫之间存在这样一种复杂关系。这种关联的复杂性取决于内生真菌与禾本科植物的关联以及存在的昆虫。内生真菌与禾本科植物关联中产生的次生化合物可为禾本科植物提供对食草动物的抗性，从而在真菌与植物之间形成互利共生关系，这对食草昆虫产生负面影响。水平传播的非禾本科II型内生真菌的研究要少得多，因此它们的生态作用尚未完全了解。这篇论坛文章从维管植物内生真菌的成熟例子出发，探讨了这种复杂三角关系中依赖关系的复杂性，以及它们如何影响自由生活和隐蔽生活（如形成虫瘿、栖息在虫瘿中）昆虫的生物学和进化。文章还讨论了将I型真菌内生菌菌株接种到禾本科植物中及其商业化的最新进展，以及内生真菌在瘿蚊科（双翅目）诱导的虫瘿中可能发挥的作用。
