beauveria bassiana

beauveria bassiana, popularly known as white fungus or green fungus, is a microorganism used in the biological control of agricultural pests.

The species is one of the most studied and applied in integrated pest management programs.

Biology

beauveria bassiana consists of an entomopathogenic ascomycete fungus. In other words, it has the ability to infect and kill insects. It is found naturally in soil, in plant remains and in environments where there is a high concentration of insects. It produces spores that are highly resistant to adverse environmental conditions, allowing it to survive for long periods.

Its taxonomic classification:

• Kingdom: Fungi

• Phylum: Ascomycota

• Class: Sordariomycetes

• Order: Hypocreales

• Family: Cordycipitaceae

• Genre: Beauveria

• Species: beauveria bassiana

The fungus belongs to the group of ascomycetes, characterized by the production of reproductive structures called ascospores. However, in most practical applications, the anamorphic (asexual) form of the fungus, which produces conidia, is the most relevant.

The basic structure of beauveria bassiana:

• Conidia: asexual reproductive structures of the fungus, responsible for the dissemination and infection of new hosts. They are unicellular spores, generally elongated or ellipsoidal in shape. They have a resistant wall that protects them against adverse conditions.

• Mycelium: After the conidia germinate, the fungus develops a mycelium, composed of branched hyphae. The mycelium colonizes the insect's body during the infection phase.

• Ascospores: In the sexual form (teleomorph), the fungus can form fruiting bodies (ascocarps) that contain ascospores. This phase is rarely observed under natural conditions.

In terms of life cycle, scientific literature points out the following in relation to beauveria bassiana:

• Conidial production: the fungus produces conidia that remain viable in the environment for long periods, waiting for favorable conditions to infect a host.

• Adhesion to insects: when conidia come into contact with the cuticle of an insect, they adhere to the surface thanks to adhesive substances present in the cell wall of the spores.

• Germination and penetration: under adequate humidity and temperature conditions, conidia germinate and form hyphae that secrete enzymes such as chitinases and proteases. These enzymes degrade the insect's cuticle, allowing the fungus to penetrate.

• Internal colonization: Once inside the insect's body, the fungus multiplies rapidly, colonizing internal tissues and competing for nutrients. During this process, the fungus also produces toxins that weaken the host's immune system.

• Insect death: Intense colonization leads to the death of the insect, usually within a few days. This phenomenon is known as "white death" due to the characteristic appearance of the corpse covered in mycelium.

• Emergence of new conidia: After the insect dies, the fungus emerges externally, forming a dense layer of white mycelium that eventually turns greenish-green as new conidia are produced. These conidia are released into the environment, restarting the cycle.

beauveria bassiana It is widely distributed in soils, plant remains and agricultural environments. It can be found on practically all continents, except in the polar regions.

Your growth requirements:

• Temperature: grows best at temperatures between 20°C and 30°C, although some strains can tolerate wider ranges.

• Humidity: high relative humidity (above 90%) is essential for conidial germination and insect infection.

• pH: the fungus prefers environments with a neutral to slightly acidic pH.

Etiology and characteristics

The mechanism of action of beauveria bassiana involves the production of proteolytic enzymes and the release of toxins that weaken the insect's immune system. When the spores come into contact with the host's body, they germinate and penetrate the cuticle, colonizing the insect's tissues internally. This process leads to the death of the host within a few days.

After the insect dies, the fungus emerges externally, covering the corpse with a layer of characteristic white mycelium, which later turns greenish due to the production of new conidia. This final phase is crucial for the spread of the fungus in the environment.

Use for insect control

It is widely used beauveria bassiana as a biological control agent against various agricultural and forestry pests.

The main target insects include:

• Caterpillars: Spodoptera frugiperda e Helicoverpa armigera are sensitive to the fungus.

• Beetles: species such as Diabrotica speciosa (cow) and hypothenemus hampei (coffee borer) are successfully controlled.

• Bed Bugs: The fungus is effective against bed bugs such as Euschistus heros.

• Leaf-cutter ants: Atta spp. And Acromyrmex spp. are also potential targets.

It is considered safe for humans, non-target animals and pollinators. It can be applied through foliar spraying, seed treatment or incorporation into the soil.