Abstract

Recent advances in research on parasitic fungi and their molecular and cellular interactions with the insect immune system have led to new insights into the complex relationships and mechanisms involved in fungal pathogenesis. This review focuses on molecules which mediate virulence of the producing fungi (fungal proteases and toxins) and on molecules contributing to the antifungal humoral immune responses of insects (antifungal proteins, protease inhibitors and detoxification proteins). Among the molecules produced by parasitic fungi during infection, at least proteolytic enzymes and toxins interfere with the host immune system in a sophisticated manner. Some of these compounds support fungal development within the infected host by suppression of its potent immune system. In particular, they impair circulating haemocytes, e.g. by damaging cytoskeletal structures and inducing apoptosis. Resistance of insects to microorganisms relies on cellular and humoral defence reactions. Although research on insect immunity attracted much attention in past decades, studies on the identification, characterization and mode of action of antifungal compounds, inducible protease inhibitors and proteins which detoxify fungal toxins in insects are more recent. Present data suggest a synergistic contribution of these proteins to antifungal defence. Successful development of parasitic fungi in infected host insects obviously requires combined activity of enzymes and immunosuppressive toxins. Current frontiers concerning the research on insect-fungal interactions at the cellular and molecular levels are outlined, with emphasis on applied aspects. Finally, a comparison of parasitic fungi with other groups of entomopathogens reveals parallels in strategies employed for evasion of host immune responses.