Fusarium, an entomopathogen—a myth or reality?

Abstract

The Fusarium species has diverse ecological functions ranging from saprophytes, endophytes, and animal and plant pathogens. Occasionally, they are isolated from dead and alive insects. However, research on fusaria-insect associations is very limited as fusaria are generalized as opportunistic insect-pathogens. Additionally, their phytopathogenicity raises concerns in their use as commercial biopesticides. Insect biocontrol potential of Fusarium is favored by their excellent soil survivability as saprophytes, and sometimes, insect-pathogenic strains do not exhibit phytopathogenicity. In addition, a small group of fusaria, those belonging to the Fusarium solani species complex, act as insect mutualists assisting in host growth and fecundity. In this review, we summarize mutualism and pathogenicity among fusaria and insects. Furthermore, we assert on Fusarium entomopathogenicity by analyzing previous studies clearly demonstrating their natural insect-pathogenicity in fields, and their presence in soils. We also review the presence and/or production of a well-known insecticidal metabolite beauvericin by different Fusarium species. Lastly, some proof-of-concept studies are also summarized, which demonstrate the histological as well as immunological changes that a larva undergoes during Fusarium oxysporum pathogenesis. These reports highlight the insecticidal properties of some Fusarium spp., and emphasize the need of robust techniques, which can distinguish phytopathogenic, mutualistic and entomopathogenic fusaria.