Definitions

deuteromycotina

Beauveria bassiana

Beauveria bassiana is a fungus that grows naturally in soils throughout the world and acts as a parasite on various insect species, causing white muscardine disease; it thus belongs to the entomopathogenic fungi. It is being used as a biological insecticide to control a number of pests such as termites, whitefly, different beetles and its use in the control of the malaria-transmitting mosquitos is under investigation.

Discovery and name

The species is named after the Italian entomologist Agostino Bassi who discovered it in 1835 as the cause of the muscardine disease of domesticated silkworms. It was formerly also known as Tritirachium shiotae.

Relation to Cordyceps and other fungi

Beauveria bassiana is the anamorph (asexually reproducing form) of Cordyceps bassiana. The latter teleomorph (the sexually reproducing form) has been collected only in eastern Asia.

The name B. bassiana has long been used to describe a complex of morphologically similar and closely related species. Rehner and Buckley have shown that B. bassiana consists of many distinct lineages that should be recognized as distinct phylogenetic species.

Morphology of the fungus

In culture, B. bassiana grows as a white mold. On most common cultural media, it produces many dry, powdery conidia in distinctive white spore balls. Each spore ball is composed of a cluster of conidiogenous cells. The conidiogenous cells of B. bassiana are short and ovoid, and terminate in a narrow apical extension called a rachis. The rachis elongates after each conidium is produced, resulting in a long zig-zag extension. The conidia are single-celled, haploid, and hydrophobic.

White muscardine disease

The insect disease caused by the fungus is called white muscardine disease. When the microscopic spores of the fungus come into contact with the body of an insect host, they germinate, penetrate the cuticle, and grow inside, killing the insect within a matter of days. Afterwards a white mold emerges from the cadaver and produces new spores. A typical isolate of B. bassiana can attack a broad range of insects; various isolates differ in their host range. The factors responsible for host susceptibility are not known.

Beauveria bassiana parasitizing the Colorado potato beetle has been reported to be, in turn, the host of a mycoparasitic fungus Syspastospora parasitica. This organism also attacks related insect-pathogenic species of the Clavicipitaceae.

Use in biological control of insects

Beauveria bassiana can be used as a biological insecticide to control a number of pests such as termites, whitefly, and many other insects. Its use in the control of the malaria-transmitting mosquitos is under investigation. As an insecticide, the spores are sprayed on affected crops as an emulsified suspension or wettable powder or applied to mosquito nets as a malaria control agent.

Beauveria bassiana parasitizes a very wide range of arthropod hosts, and so should be considered a nonselective biological insecticide. It should not be applied to flowers visited by pollinating insects .

Known targets include :

  • Aphids
  • Whiteflies
  • Bugs
  • Mealybugs
  • Psyllids

*Lygus bugs
*Chinch bug

  • Grasshoppers
  • Thrips
  • Termites
  • Fire ants
  • Flies

*Fungal gnats
*Shoreflies

  • Beetles

*Coffee borer beetle
*Colorado potato beetle
*Mexican bean beetle
*Japanese beetle
*Boll weevil
*Cereal leaf beetle
*Bark beetles
*Black vine weevil
*Strawberry root weevil

  • Caterpillars

*European corn borer
*Codling moth
*Douglas fir tussock moth
*Silkworm

  • Mites

The fungus rarely infects humans or other animals, so it is generally considered safe as an insecticide. However, at least one case of human infection by B. bassiana has been reported in a person with a suppressed immune system. Additionally, like any powder, the spores may exacerbate breathing difficulties. Wagner and Lewis reported the ability of B. bassiana to grow as an endophyte in corn.

See also

References

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