Metarhizium species are arthropod pathogens with a wide range of hosts and geographical distribution. They are parasitic on insects and saprophytic in the soil.
Metarhizium anisopliae is a naturally occurring bacterium that has been isolated from a variety of arthropods and decaying materials. As a parasite, it causes the sickness known as green muscardine disease in a variety of insects. Entomo-pathogenic fungi have been utilized as bio-control agents against agricultural pests since the 19th century. It was used to combat the wheat grain beetle as well as the sugar cane pest. It has been intensively researched and cultured as a potential pesticide replacement.
Metarhizium anisopliae has been discovered colonizing the rhizosphere and sticking to the surfaces of plant roots, and it has the potential to dramatically alter this ecological niche by repelling and killing a wide range of insects. The potential use of such fungus for managing vectors of human and animal diseases has lately been examined, and the results have been promising. However, it is now available as a commercial product that is used to manage a variety of insect pests with no harmful effects on humans or the environment.
When Metarhizium anisopliae spores come into contact with the cuticle (skin) of susceptible insects, they germinate and grow right through the cuticle to the host’s inner body. The fungus spreads throughout the insect’s body, sucking up nutrients and draining them. Adhesion, germination, appressorium formation, penetration, colonization of hemolymph, and extrusion and sporulation are the six stages of infection in Metarhizium spp., which are also observed in other entomopathogenic fungi. It can infest 6 species, 15 pest groups, 200 insect species, bed bugs, and mites, as well as root weevils, planthoppers, white grub, and termites.
The fungus produces serine proteases, which are cuticle-degrading proteases that are harmful to insects.
According to studies, the infection cycle goes like this:
(1) host attachment and germination,
(2) epicuticle destruction,
(3) blastospore formation,
(4) insecticidal metabolite killing, and
(5) hyphal extrusion and conidiation.
These fungi also help plants grow by collecting phosphorus and other minerals, extracting nitrogen from decaying organic materials, and assisting in the carbon storage process. Mineral nutrients (particularly phosphorus and nitrogen) are among the most critical limiting variables for plant growth in natural ecosystems, hence the advantages to the plant will be conditional on soil fertility.
In conclusion, M. anisopliae, is a potential biocontrol agent of termites, mosquitoes, and cattle ticks. However, many challenges, such as the slow mode of action and unpredictable results of the application of these fungi, have to be overcome to maximize the efficacy. Studies are being conducted to speed up the mode of action by genetically engineering M. anisopliae. The effects of these fungi on the effects of non-target organisms and the environment should also be considered before using them in the field.
