|This article does not cite any references or sources. (June 2011)|
Typical life cycle
These fungi usually attach to the external body surface of insects in the form of microscopic spores (usually asexual, mitosporic spores also called conidia). Under permissive conditions of temperature and (usually high) moisture, these spores germinate, grow as hyphae and colonize the insect's cuticle; eventually they bore through it and reach the insects' body cavity (hemocoel). Then, the fungal cells proliferate in the host body cavity, usually as walled hyphae or in the form of wall-less protoplasts (depending on the fungus involved). After some time the insect is usually killed (sometimes by fungal toxins) and new propagules (spores) are formed in/on the insect if environmental conditions are again permissive; usually high humidity is required for sporulation.
The entomopathogenic fungi include taxa from several of the main fungal groups and do not form a monophyletic group. Many common and/or important entomopathogenic fungi are in the order Hypocreales of the Ascomycota: the asexual (anamorph) phases Beauveria, Metarhizium, Nomuraea, Paecilomyces = Isaria, Hirsutella and the sexual (teleomorph) state Cordyceps; others (Entomophthora, Zoophthora, Pandora, Entomophaga) belong in the order Entomophthorales of the Zygomycota.
Since they are considered natural mortality agents and environmentally safe, there is worldwide interest in the use and manipulation of entomopathogenic fungi for biological control of insects and other arthropod pests. In particular, the asexual phases of Ascomycota (Beauveria spp., Lecanicillium spp., Metarhizium spp., Paecilomyces spp. and others) are under intense scrutiny due to the traits favouring their use as biological insecticides.
Production. Most entomopathogenic fungi can be grown on artificial media. However, some require extremely complex media; others, like Beauveria bassiana and exploitable species in the genus Metarhizium, can be grown on starch-rich substrates like cereal grains (rice, wheat).
Virulence. The Entomophthorales are often reported as causing high levels of mortality (epizootics) in nature. These fungi are highly virulent. The anamorphic Ascomycota (Metarhizium, Beauveria etc.) are reported as causing epizootics less frequently in nature.
See the desert locust page for more on use of Metarhizium as a biological insecticide.