Biological relationships between Fusarium fungi and insects (review)

Fusarium fungi are characterized by high metabolic activity and adaptability. They colonize plant substrates, participate in the destruction of organic materials and in soil formation, and can be harmful to insects and mammalians. Fusarium fungi and insects coexist in different biotopes. Using molecular methods to classify 140 fungi samples, isolated from insects, K. O’Donnell et al. (2012) identified at least 23 strains or strain complexes as the Fusarium species. A host range specificity of Fusarium fungi to insects is no still found. The co-evolution of these groups of organisms has resulted in the emergence of various forms of interactions between them. The antagonistic forms have unilateral action, which can lead to lethal and non-lethal effects to insects. In both cases, this interaction involves volatile (e.g., repellent) and nonvolatile (e.g., mycotoxins) secondary metabolites of fungi. Volatile organic compounds (VOCs) are the signal molecules (infochemicals, semiochemicals) which act as the insect pheromones, allomones, kairomones, etc. The research of Fusarium fungi VOC was initiated in the late 1990s, and there are few scientific publications on the subject for the time being. The Fusarium VOCs were shown to consist of a large number of components from the different groups of chemical compounds. The mechanisms, due to which the infestation of entomopathogenic Fusarium fungi into host insects occurs, differ fundamentally from those observed in other fungi: the Fusarium fungi enter the insect’s body through natural orifices, such as mouthparts, spiracles, ovipositor, or wounds, but not through the cuticle. Symbiotic interactions between Fusarium fungi and insects are very diverse and include both mutually beneficial co-existence (mutualism) and forms that could be described as commensalism. The role of insects in spreading of Fusarium spores on new substrates is well documented. An attractive effect of biologically active volatile metabolites of fungi has been shown. In a number of cases Fusarium fungi are a source of substances that are essential to maintain normal growth and development of some insects. Obviously, the various forms of relationships between Fusarium fungi and insects are an important evolutionary factor. Diverse forms of interactions between Fusarium fungi and insects allow forming their sustainable self-regulating ecosystems. Special attention is paid to possible interactions of Fusarium fungi and insect pests in case of their sharing cereal grains as an alimentary substrate.