Metarhizium anisopliae is a mitosporic or anamorphic fungus of asexual reproduction, widely used as an entomopathogen for biological control. It has the ability to parasitize and eliminate a wide range of insect pests of various plants of agricultural importance..
This fungus has special adaptation characteristics to survive in a saprophytic way on organic matter and as a parasite on insects. Most commercial crop pest insects are susceptible to being attacked by this entomopathogenic fungus..
As a saprophytic life organism it is adapted to different environments where it develops mycelium, conidiophores and conidia. This ability facilitates its reproduction at the laboratory level through simple propagation techniques to be used as a biocontroller..
Indeed, this entomopathogenic fungus is the natural enemy of a large number of insect species in various agroecosystems. The hosts are completely covered by a green mycelium, in reference to the disease called green muscardina.
The life cycle of the entomopathogen Metarhizium anisopliae It is carried out in two phases, a cellular infective phase and another saprophytic phase. The infective within the parasitized insect and in the saprophyte takes advantage of the nutrients of the corpse to multiply.
Unlike pathogens such as viruses and bacteria that need to be ingested by the pathogen to act, the Metarhizium fungus acts on contact. In this case, the spores can germinate and penetrate the interior, infecting the host's cuticular membrane..
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The Metarhizium anisopliae It is a broad spectrum pathogenic fungus, located in the soil and the remains of parasitized insects. Due to its potential as an ecological alternative, it is the ideal substitute for the agrochemicals used in the integral management of pests of economic importance..
Infection of the M. anisopliae It begins with the union of the conidia of the fungus to the cuticle of the host insect. Subsequently, through the enzymatic activity between both structures and the mechanical action, germination and penetration occurs..
Enzymes that intervene in the recognition, adhesion and pathogenesis of the host's cuticle are located in the fungal cell wall. These proteins include phospholipases, proteases, dismutases and adhesins, which also act in the adhesion, osmosis and morphogenesis processes of the fungus..
Generally, these fungi are slow-acting when environmental conditions are unfavorable. Average temperatures between 24 and 28 ºC, and high relative humidity are ideal for an effective development and entomopathogenic action.
The green muscardina disease caused by M. anisopliae it is characterized by the green coloration of the spores on the colonized host. Once the insect is invaded, the mycelium covers the surface, where the structures fructify and sporulate, covering the surface of the host..
In this regard, the infection lasts about a week for the insect to stop feeding and die. Among the various pests it controls, it is highly effective on insects of the order Coleoptera, Lepidoptera, and Homoptera, particularly larvae..
The mushroom M. anisopliae As a biocontroller, it is marketed in spore formulations mixed with inert materials to preserve its viability. The suitable way for its application is through fumigations, environmental manipulation and inoculation.
At the laboratory level, colonies of M. anisopliae show an effective development in PDA (Papa-dextrorse-agar) culture media. The circular colony presents a white micellar growth initially, exhibiting color variations when the fungus sporulates.
When the conidia multiplication process begins, an olive-green color is perceived on the micellar surface. On the underside of the capsule, a pale yellow discoloration is observed with diffuse yellow pigments in the middle.
The conidiophores grow from the mycelium in an irregular shape with two to three branches on each septum. These conidiophores are 4 to 14 microns long and 1.5 to 2.5 microns in diameter..
The phialides are structures that are generated in the mycelium, being the place where the conidia detach. On M. anisopliae are thin at the apex, 6 to 15 microns in length and 2 to 5 microns in diameter.
Conidia are unicellular structures, cylindrical and truncated, with long chains, hyaline to greenish. Conidia are 4 to 10 microns long and 2 to 4 microns in diameter.
The gender Metarhizium was initially described by Sorokin (1883) infecting larvae of Austrian Anisoplia, causing a disease known as green muscardina. Name Entomophthora anisopliae was initially proposed by Metschnikoff for fungal isolates, later it was named Isaria destroyer.
More detailed studies of the taxonomy of the genus, concluded in classifying it as Metarhizium sorokin. Currently the species is considered M. anisopliae, named by Metschnikoff, as the representative organism of the genus Metarhizium.
Various isolates of the fungus Metarhizium they are specific, which is why they have been designated as new varieties. However, they are currently classified as species Metarhizium anisopliae, Metarhizium majus Y Metarhizium acridum.
Likewise, some species have been renamed, Metarhizium taii presents characteristics similar to Metarhizium guizhouense. A commercial strain of M. anisopliae, the M. anisopliae (43) which is specific enemy of coleoptera is now called Metarhizium brunneum.
The species Metarhizium anisopliae (Metchnikoff) Sorokin (1883), is part of the genus Metarhizium described by Sorokin (1883). Taxonomically it belongs to the family Clavicipitaceae, order Hypocreales, class Sordariomycetes, division Ascomycota, of the kingdom Fungi.
The mushroom Metarhizium anisopliae initiates pathogenesis through the adhesion process of conidia on the host's cuticular membrane. Subsequently, the phases of germination, growth of appressoria or insertion structures, colonization and reproduction occur..
The spores or conidia from the soil or contaminated insect remains, invade the cuticle of new hosts. With the intervention of mechanical and chemical processes, the appressorium and the germ tube that penetrates the interior of the insect develop.
Generally, under favorable conditions, germination occurs 12 hours after inoculation. Likewise, the formation of appressoria and the penetration of the germ tube or haustoria occurs between 12 to 18 hours..
The physical mechanism that allows penetration is the pressure exerted by the appressoria, which breaks the cuticular membrane. The chemical mechanism is the action of protease, kinase and lipase enzymes that break down the membranes at the site of insertion.
Once the insect has penetrated, the hyphae branch inside, completely invading the prey after 3-4 days. Then the reproductive structures, conidiophores and conidia are formed, which completes the pathogenesis of the host at 4-5 days.
The death of the insect occurs through the contamination of toxins produced by the entomopathogenic fungus. The biocontroller synthesizes the toxins dextruxin, protodextruxin and demethyldextruxin with a high level of toxicity for arthropods and nematodes.
The invasion of the host is conditioned to the temperature and relative humidity of the environment. Likewise, the availability of nutrients on the insect's cuticular membrane and the ability to detect hosts susceptible to being colonized..
Green muscardina disease caused by Metarhizium anisopliae It presents various symptoms on infected larvae, nymphs or adults. Immature forms reduce mucilage formation, tend to move away from the attack site or paralyze its movement.
Adults decrease their movement and flight area, stop feeding, and females do not lay eggs. Contaminated insects tend to die in places far from the site of infection, which encourages the spread of the disease.
The disease cycle can last between 8 and 10 days depending on the environmental conditions, mainly humidity and temperature. After the death of the host, it is completely covered by a white mycelium and successive green sporulation, characteristic of green muscardina..
The mushroom Metarhizium anisopliae it is one of the most widely studied and used entomopathogens in biological pest control. The key factor for the successful colonization of a host is the penetration of the fungus and subsequent multiplication..
Once the fungus is established within the insect, the proliferation of filamentous hyphae occurs and the generation of mycotoxins that inactivate the host. The death of the host also occurs due to pathological changes and mechanical effects on internal organs and tissues..
Biological control is carried out by applying products formulated based on concentrations of spores or conidia of the fungus in commercial products. Conidia are mixed with inert materials, such as solvents, clays, talcs, emulsifiers, and other natural additives.
These materials must not affect the viability of the fungus and must be harmless to the environment and the crop. In addition, they must present optimal physical conditions that facilitate mixing, application of the product and are low cost..
The success of biological control through entomopathogens depends on the effective formulation of the commercial product. Including the viability of the microorganism, the material used in the formulation, the storage conditions and the method of application.
The inoculum from applications of formulated with the fungus M. anisopliae It serves to contaminate larvae, hyphae or adults. Contaminated hosts migrate to other places in the crop where they die and spread the disease due to sporulation of the fungus.
The action of wind, rain and dew facilitates the dispersal of the conidia to other parts of the plant. Insects in their foraging activity are exposed to the adhesion of spores.
The environmental conditions favor the development and dispersal of the conidia, the immature stages of the insect being the most susceptible. From new infections, secondary foci are created, proliferating the epizootic capable of fully controlling the plague.
The black weevil (Cosmopolites sordidus Germar) is an important pest of the cultivation of musaceae (plantain and banana) mainly in the tropics. Its dispersion is caused mainly by the management that man performs in the sowing and harvesting processes..
The larva is the causal agent of the damage caused inside the rhizome. The weevil in its larval phase is very active and voracious, causing perforations that affect the root system of the plant..
The galleries formed in the rhizome facilitate contamination with microorganisms that rot the vascular tissues of the plant. In addition to this, the plant weakens and tends to overturn due to the action of strong winds..
The usual control is based on the use of chemical insecticides, however, their negative effect on the environment has led to the search for new alternatives. Currently the use of entomopathogenic fungi such as Metarhizium anisopliae have reported good results in field trials.
Excellent results have been obtained in Brazil and Ecuador (85-95% mortality) using M. anisopliae on rice as inoculation material. The strategy is to place infected rice on pieces of stem around the plant, the insect is attracted and becomes contaminated with the pathogen.
The Fall ArmywormSpodoptera frugiperda) is one of the most damaging pests in cereals such as sorghum, corn and forages. In corn it is highly damaging when it attacks the crop before 30 days, with heights between 40 and 60 cm..
In this regard, chemical control has allowed the insect to achieve greater resistance, elimination of natural enemies and damage to the environment. The use of M. anisopliae as a biological control alternative has reported good results, since S. frugiperda it is susceptible.
The best results have been obtained when using sterilized rice as a means of dispersing the inoculum in the culture. Performing applications at 10 dds and then at 8 days, adjusting the formulation at 1 × 1012 conidia per hectare.
Beetle larvae are found feeding on organic matter and roots of economically important crops. The species Hylamorpha elegans (Burmeister) called green chicken, is its larval state is a pest of wheat (Triticum aestivum L.).
The damage caused by the larvae occurs at the level of the root system, causing the plants to weaken, wilt and lose their leaves. The life cycle of the beetle lasts one year, and in the time of greatest incidence, totally destroyed cultivation areas are observed.
Chemical control has been ineffective due to the migration of the larvae in the treated soils. Associated with increased resistance, increased production costs and environmental contamination.
The employment of Metarhizium anisopliae As an antagonist and biocontroller agent, it has achieved up to 50% mortality in larval populations. Even though the results have been obtained at the laboratory level, it is expected that field analyzes will report similar results..
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