Beauveria bassiana (Bals.-Criv.) Vuill.

Beauveria bassiana is a fungus that grows naturally in soils throughout the world and acts as a parasite on various arthropod species, causing white muscardine disease; it thus belongs to the group of entomopathogenic fungi. It is used as a biological insecticide to control a number of pests, including termites, thrips, whiteflies, aphids, and various beetles. Its use in the control of bed bugs and malaria-transmitting mosquitos is under investigation.

Taxonomy

The species is named after Italian entomologist Agostino Bassi, who discovered it in 1835 in silkworms (Bombyx mori). Bassi performed the first infection experiments, and determined the fungus to be the cause of the muscardine disease, which then led to carriers transmitting it by airborne means. Later the same year, the fungus was named Botrytis bassiana by Giuseppe Gabriel Balsamo-Crivelli. The species epithet honours Bassi, the discoverer.

In 1911, Jean Beauverie did further study, and the next year, Jean Paul Vuillemin made it the type species of his new genus, Beauveria, a name that honors Beauverie.

The name B. bassiana has long been used to describe a species complex of morphologically similar and closely related isolates. Rehner and Buckley have shown that B. bassiana consists of many distinct lineages that should be recognized as distinct phylogenetic species and the genus Beauveria was redescribed with a proposed type for B. bassiana in 2011.

The species was formerly also known as Tritirachium shiotae, among other synonyms.

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.

Description

B. bassiana is a white mold when grown on culture, producing white spore balls made up of many conidia that are single-celled, haploid, and hydrophobic. The short, ovoid conidiogenous cells that produce the conidia have a narrow apical extension called a rachis, which elongates into a long zig-zag extension.

Ecology

The insect disease caused by the fungus is a muscardine, which has been 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.

B. 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.

A fungus attributed to be B. bassiana was observed to cause infections in a captive American alligator and B. bassiana was implicated in causing a pulmonary disease in captive tortoises. The reptiles were in captivity and under temperature stress which may explain their susceptibility to the fungus. When a tortoise was kept at 22 °C and injected with 0.5 mL of 106 spores of B. bassiana into the lung, no mortality was observed, while a second contaminated tortoise died when kept only at 16 °C.

A microevolutionary experiment in 2013 showed that the greater wax moth (Galleria mellonella) was able to adapt its defense mechanisms during 25 generations, while being under constant selective pressure from B. bassiana. The moth developed resistance, but apparently at a cost.

Wagner and Lewis reported the ability of B. bassiana to grow as an endophyte in corn.

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