Beauveria bassiana

The species is named after the Italian entomologist Agostino Bassi, who discovered it in 1815 as the cause of the muscardine disease which then led to carriers transmitting it by airborne means. It was formerly also known as Tritirachium shiotae. The name B. bassiana has long been used to describe a species complex of morphologically similar and closely related isolates. Rehner and Buckley [3] 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.[4] In light of this work and the known existence of cryptic species, it is important to characterise isolates used to develop biological insecticides.

White muscardine disease

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. The factors responsible for host susceptibility are not known.

Spotted in St. Tammany Parish, Louisiana a Golden silk orb-weaver dead from white muscardine disease with white mold emerging from the cadaver's joints and pores.

Beauveria bassiana parasitizing the Colorado potato beetle has been reported to be, in turn, the host of a mycoparasitic fungus Syspastospora parasitica.[6] This organism also attacks related insect-pathogenic species of the Clavicipitaceae.

In culture, B. bassiana grows as a white mould. 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.

Beauveria bassiana can be used as a biological insecticide to control a number of pests such as termites, whiteflies, and many other insects. Its use in the control of malaria-transmitting mosquitos is under investigation.[2] As an insecticide, the spores are sprayed on affected crops as an emulsified suspension or wettable powder or applied to mosquito nets as a mosquito control agent.

As a species, Beauveria bassiana parasitizes a very wide range of arthropod hosts. However, different strains vary in their host ranges, some having rather narrow ranges, like strain Bba 5653 that is very virulent to the larvae of the diamondback moth and kills only few other types of caterpillars. Some strains do have a wide host range and should, therefore, be considered nonselective biological insecticides. These should not be applied to flowers visited by pollinating insects.[7]

Known targets include:[8][9][10]

• Aphids
• Whiteflies
• Mealybugs
• Psyllids
  • Chinch bug
  • Lygus bugs
• Grasshoppers
• Stink bugs (Halyomorpha halys)[11]
• Thrips
• Termites
• Fire ants
• Flies
• Stem borers
  • Fungal gnats
  • Shoreflies
• Beetles
  • Bark beetle[12]
  • Black vine weevil
  • Boll weevil
  • Cereal leaf beetle
  • Coffee borer beetle
  • Colorado potato beetle
  • Emerald ash borer (in conjunction with the parasitoid wasp Tetrastichus planipennisi)[13]
  • Japanese beetle
  • Mexican bean beetle
  • Red palm weevil[14]
  • Strawberry root weevil
• Caterpillars
  • Codling moth
  • Douglas fir tussock moth
  • European corn borer
  • Invasive silkworms
  • Apple clearwing moth[15]
• 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.[16] Additionally, the spores may exacerbate breathing difficulties. Wagner and Lewis reported the ability of B. bassiana to grow as an endophyte in corn.[17]

A fungus attributed to be B. bassiana was observed to cause infections in a captive American alligator[18] and B. bassiana was implicated in causing a pulmonary disease in captive tortoises.[19][20] 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.[21]

Preliminary research has shown the fungus is 100% effective in eliminating bed bugs exposed to cotton fabric sprayed with fungus spores. It is also effective against bed bug colonies due to B. bassiana carried by infected bugs back to their harborages. All subjects died within 5 days of exposure.[1]

In March 2013, genetically modified Beauveria bassiana was found in a number of research laboratories and greenhouses outside of a designated containment area at Lincoln University in Christchurch, New Zealand. The Ministry for Primary Industries investigated the leak.[22]

• Biological insecticides
• Metarhizium spp. which cause "green muscardine" disease

• Luz C, Rocha LF, Nery GV, Magalhães BP, Tigano MS (March 2004). "Activity of oil-formulated Beauveria bassiana against Triatoma sordida in peridomestic areas in Central Brazil". Mem. Inst. Oswaldo Cruz. 99 (2): 211–8. doi:10.1590/S0074-02762004000200017. PMID 15250478.
• Prior C, Jollands P, Le Patourel G (1988). "Infectivity of oil and water formulations of Beauveria bassiana (Deuteromycotina; Hyphomycetes) to the cocoa weevil pest Pantorhytes plutus (Coleoptera: Curculionidae)". Journal of Invertebrate Pathology. 52 (1): 66–72. doi:10.1016/0022-2011(88)90103-6.