Metarhizium anisopliae

Metarhizium anisopliae 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. It is 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.



The disease caused by the fungus is called green muscardine disease because of the green color of its spores. When these mitotic (asexual) spores (properly 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 mold 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 strains that are adapted to certain groups of insects. Some strains are so specific that they have attained variety status, like Metarhizium anisopliae var. acridum, which almost exclusively infects grasshoppers in the suborder Caelifera of the Orthoptera.

The fungus 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; the plan for malaria control is to coat mosquito nets or cotton sheets attached to the wall with them. The level of insect control (mortality) in general depends on factors like the number of spores applied against the insect host, the fungus strain used, the formulation and weather conditions. Oil-based formulations allow the application of fungal spores under dry conditions.

Metarhizium anisopliae (also known as Entomophthora anisopliae in the early 1900s) was named after the insect species it was originally isolated from, the beetle Anisoplia austriaca. It is a mitosporic fungus with asexual reproduction for which a teleomorph has not yet been discovered. Cordyceps taii was shown to be the teleomorph of Metarhizium taii, so it seems likely that the one of M. anisopliae will also turn out to be a Cordyceps species. However, it is also possible that some, if not most, strains of M. anisopliae have lost the capability of reproducing sexually.

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. The fungus is now a candidate for mass production of the enzyme.