Entomopathogenic fungus

An entomopathogenic fungus is a fungus that can act as a parasite of insects and kills or seriously disables them.  

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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.

Groups

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 (anamorphic) phases Beauveria, Metarhizium, Nomuraea, Paecilomyces = Isaria, Hirsutella and the sexual state Cordyceps; others (Entomophthora, Zoophthora, Pandora, Entomophaga) belong in the order Entomophthorales of the Zygomycota.

Related fungi attack and kill other invertebrates (e.g nematodes).

Use of entomopathogenic fungi in the biological control of pests

Since they are considered natural mortality agents and environmentally safe, there is worldwide interest in the utilization and manipulation of entomopathogenic fungi for biological control of insects and other arthropod pests. In particular, the asexual phases of Ascomycota (Beauveria, Metarhizium, Paecilomyces and others) are under intense scrutiny due to the traits favoring their use as bioinsecticides.

Production. Most entomopathogenic fungi can be grown on artificial media. However, some require extremely complex media; others, like Beauveria bassiana and Metarhizium anisopliae, 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.

Also important are their properties regarding specificity (host range), storage, formulation, and application.

See the desert locust page for use of Metarhizium as a bioinsecticide.