Metarhizium anisopliae

Metarhizium anisopliae, formerly known as Entomophthora anisopliae (basionym), is a fungus that grows naturally in soils throughout the world and causes disease in various insects by acting as a parasite; it thus belongs to the entomopathogenic fungi^[1]. It is known to infect over 200 insect species, including termites. It is currently being used as a biological insecticide to control a number of pests such as grasshoppers, termites, thrips, etc. and its use in the control of malaria-transmitting mosquitos is under investigation^[2].

The disease caused by the fungus is called green muscardine disease because of the green colour of its spores. When these mitotic (asexual) spores (called conidia) of the fungus come into contact with the body of an insect host, they germinate and the hyphae that emerge penetrate the cuticle. The fungus then develops inside the body eventually killing the insect after a few days; this lethal effect is very likely aided by the production of insecticidal cyclic peptides (destruxins). The cuticle of the cadaver often becomes red. If the ambient humidity is high enough, a white mould then grows on the cadaver that soon turns green as spores are produced. Most insects living near the soil have evolved natural defenses against entomopathogenic fungi like M. anisopliae. This fungus is therefore locked in an evolutionary battle to overcome these defenses, which has led to a large number of isolates (or strains) that are adapted to certain groups of insects^[3].

Some isolates are so specific that they have attained variety status, like Metarhizium anisopliae var. acridum^[4], which almost exclusively infects grasshoppers in the suborder Caelifera of the Orthoptera. Various research groups, including the international LUBILOSA Programme, have identified key technical challenges in the development of mycoinsecticide products including: isolate selection, mass production and delivery systems (formulation and application)^[5]. In other words, insect control (mortality) depends on factors like the number of spores applied against the insect host, the formulation^[6] and weather conditions^[7]. Oil-based formulations allow the application of fungal spores under dry conditions, and is compatible with existing Ultra-Low Volume (ULV) application techniques for locust control.

Ilya I. Mechnikov named Metarhizium anisopliae after the insect species it was originally isolated from, the beetle Anisoplia austriaca. It is a mitosporic fungus with asexual reproduction, which was formerly classified in the form class Hyphomycetes of the form phylum Deuteromycota (also often called Fungi Imperfecti). The Deuteromycota were used to bring together all fungi for which no sexual stage (teleomorph) was known. It is therefore not a real taxon in the classical sense. With the advent of genetic profiling, it has now become possible to place these fungi in proper taxa. Most turn out to be the asexual forms (anamorphs) of fungi in the phylum Ascomycota. The teleomorphs of Metarhizium species appear to be members of the genus Metacordyceps^[8]. Metacordyceps taii (as Cordyceps taii) has been described as the teleomorph of Metarhizium taii^[9], but the latter was later synonymised with Metarhizium anisopliae var. anisopliae^[10]. This means that Metacordyceps taii can now be considered the teleomorph of M. a. anisopliae. It is not yet clear whether the other varieties of M. anisopliae have their own teleomorphs. It is, however, possible that some, if not most, strains of M. anisopliae have lost the capability of reproducing sexually.

M. anisopliae does not appear to infect humans or other animals and is considered safe as an insecticide. The microscopic spores are typically sprayed on affected areas. A possible technique for malaria control is to coat mosquito nets or cotton sheets attached to the wall with them.

In August 2007, a team of scientists at the Indian Institute of Chemical Technology discovered a more efficient way of producing biodiesel which uses lipase, an enzyme produced in significant quantities by Metarhizium anisopliae; as opposed to other reactions which use enzymes that require heat in order to become active, the reaction that uses lipase runs at room temperature. The fungus is now a candidate for mass production of the enzyme.

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