Mode of action of Beauveria bassiana against insects

The infection cycle of Beauveria bassiana in invertebrates bodies has been depicted by Mascarin and Jaronski (2016) Asexual spores (conidia) are dispersed by wind, rain splashing or even by arthropod vectors facilitating the fungus to establish infection on susceptible hosts (OrtizUrquiza and Keyhani 2013).

The host infection by the fungus occurs in four steps: adhesion, germination and differentiation, penetration, and dissemination.

  • 1st step: adhesion.

It is characterized by recognition and compatibility mechanisms of conidia of the host cuticle cells (Vey et al. 1982 reported by De Kouassi 2001). Conidia (or in some cases blastospores) were attached to insect’s cuticle by electrostatic and chemical forces (Mascarin and Jaronski 2016). Then, through the production of mucilage, they induced epicuticular modification (Wraight and Roberts 1987) leading to conidia germination.

  • 2nd step: germination-differentiation.

Germination is a process that depends on environmental conditions, host physiology (biochemical composition of the host cuticle) as well. Such conditions can stimulate or inhibit it (Butt et al. 1995; Butt and Beckett 1994; Smith and Grula 1982; St Leger et al. 1989b). When conditions are suitable, conidia or blastospores germination leads to germ tubes formation. In fact, conidia germinate and form a germ tub with rehydration and chemical stimuli (Mascarin and Jaronski 2016). Differentiation is characterized by the appressoria or penetration peg establishment, which serves as inking point, softening the cuticle and promoting penetration. For this purpose, the germ tub may form a specialized structure, namely appressorium (i.e., an enlarged cell expression bearing key hydrolytic cuticle-degrading enzymes) or penetration peg enabling hyphae growth to breach the host integument (De Kouassi 2001; Mascarin and Jaronski 2016). However, appressoria production is highly dependent on nutritional value of the host cuticle (Magalhaes et al. 1988; St Leger et al. 1989a). A nutritious cuticle may stimulate mycelial growth rather than penetration (St Leger et al. 1989a).

  • 3rd step: penetration.

From the appressorium or penetration peg and with the hydrolytic action of enzymes (proteases, chitinases, lipases: the most important being proteases), mechanical pressure, and other factors (such as oxalate), the fungus is able to penetrate all cuticle layers until reaching a nutrient-rich environment, i.e. the insect hemolymph.

  • 4th step: dissemination within the host and to another host.

In the hemolymph, the fungus undergoes a morphogenetic differentiation from filamentous growth to single-celled, yeast-like hyphal bodies or blastospores that strategically exploit nutrients, colonize internal tissues, and disturb the host immune system. During this stage of the infection, the fungus can also secrete toxic metabolites that help to overcome the insect’s immune defense mechanisms for successfully colonization. Some strains produce non-enzymatic toxins such as beauvericin, beauverolides, bassianolides, and isarolides increasing the speed of the infection process (Hajeck and StLeger 1994; Roberts 1981). These events eventually lead to the death of host that became mummified. When the infected insect dies, the fungus produces an antibiotic called “Oosporin” that is used to overcome bacteria competition in insect gut (De Kouassi 2001). Then, B. bassiana hyphae cross the insect integument preferentially at the inter-segmental level and then become cottony white. Finally, conidiophores appear on the mummified cadavers after a few days and bear newly infection conidia (sporulation) for dispersal (passive dissemination).

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 Application of Beauveria bassiana

The “white muscardine” fungus which is known as Beauveria bassiana is one of several entomopathogenic fungal organisms that are labeled for use in managing a wide array of insects in greenhouses and in nurseries. Beauveria bassiana as an entomopathogenic fungus have the capacity to penetrate the cuticle and kill almost every insect that it comes in contact with. While this is generally a good thing, Beauveria bassiana may also kill some biocontrol agents like ladybird beetles if they become exposed to it.

Ladybird beetles inadvertently killed by the “white muscardine fungus” (Beauveria bassiana) in a PA greenhouse. Photo by Tom Ford, Penn State

Beauveria bassiana is considered by many entomologists as one of the more effective biocontrol agents to deploy as a plug or cutting dip. Insects and some mites when exposed to this entomopathogenic fungus typically die within 4-5 days after exposure.

Source:https://extension.psu.edu/greenhouse-pest-prevention-with-beauveria-bassiana

Beauveria bassiana

The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) has been exploited extensively to control insects that affect crops or are vectors of human and animal diseases.

Besides its entomopathogenic lifestyle, evidence has demonstrated that some Beauveria bassiana species are able to grow endophytically inside the plants and confer protection against pests and pathogens of different host plants therefore defining its role in agricultural crop production systems.

Furthermore, studies also report that combinatorial approaches may improve pest control and infectivity of Beauveria bassiana. This article reviews literature on the biological control abilities of Beauveria bassiana against pests of livestock as well as pathogens and pests of plants in the greenhouse and field.

Beauveria bassiana

Beauveria bassiana is an entomopathogenic fungus that causes white muscardine disease in a range of insects including whiteflies, aphids, thrips, grasshoppers and certain types of beetles and mites.

It differs from Nosema locustae in that it does not need to be ingested by the host; Beauveria bassiana spores simply need to come in contact with a host.

Once the host insect is infected, the fungus rapidly grows inside of the insect, feeding on the nutrients present in the host’s body and producing toxins in the process.

When the host dies, the Beauveria bassiana covers the carcass in a layer of white mold that produces more infective spores.

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Microbial control of thrips

Polyphagous thrips are among the most important economically pests that cause serious damage in various ornamental and vegetable crops throughout the world.

Because of their small size and cryptic habits, a number of thrips species are easy to invade into new areas. For a long period, thrips control has mainly relied on frequent use of insecticides, which lead to a series of ecological problems.

Although a number of alternative management tactics have been developed in many cropping systems, many invasive thrips continue to spread internationally and display vast damage potential. Microbial control of thrips includes the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, Isaria fumosorosea and Lecanicillium lecanii. The strains of fungal pathogens that were screened and proven to be effective for control of thrips should be developed worldwide and available for growers.

Applications of Beauveria Bassiana

CropsTargetsApplication way & dosage
ChivesLeek MaggotSpread 90-120g/mu (30billion WP)
CitrusRed spiderSpray 500-1500 times diluted (10billion OD)
TomatoTrialeurodes
vaporariorum
(Westwood)
Spray 40-80ml/mu
CornSpodoptera frugiperdaSpray 45-60g/mu (30billion WP)
40-80ml /mu (10billion OD)
CornCorn borerSpray 100-120g/mu (30billion WP)
ForestAmerican White MothSpray 1200-2000 times diluted (30billion WP)

Formulation Types:

1×10^10 spores/ml OD

3×10 ^10 spores/g WP