Bio-insecticides are a greatly advantageous alternative to the usual chemically formulated insecticides. They are biodegradable, eco friendly, non-poisonous and cost efficient. The foundations for microbial pest control can be traced back to the dawn of 19th century, when the Italian scientist A Bassi spent a long, more than thirty years working with white muscardine disease in silkworms. He identified Beauveria bassiana, which is named so in his tribute, as the causative agent of the disease. The fungus Beauveria bassiana wildly grow in soils all around the globe and function as a parasite on different species of insects, resulting in white muscardine disease. It is thus a member of the entomopathogenic fungi. It is broadly used as bio-insecticide for the pest management of agricultural, forest and ornamental plants. Bio-pesticides formulated on the basis of B. bassiana are useful against variety of species of thrips, whitefly, some caterpillars, meal bugs, aphida, termites, beetle and also several species of leaf-nibbling pests. The fungus is usually known as "Sugar Icing" Fungus. B bassiana forms powdery white conidial (non-motiles pores of a fungus ) masses. The conidia are globose to broadly ellipsoid and measure about 2.5-3.5 µm in diameter.
Insects differ in vulnerability to different strains. Various strains have been gathered from affected insects, cultured, spores extracted and formulated into a sprayable product for commercial utilization. Beauveria bassiana kills the pest by parasitisation which results when the insect comes in contact with fungal spores. Contact between insects and B bassiana spores occur during one of the following circumstances
• When spores are directly sprayed on insects.
• When insects contact/move on a surface where spores are deposited.
• When insects consume plants over which spores have been sprayed.
As the fungal spores attach to the cuticle of the insect, they get germinated producing the structures called hyphae that penetrate the insect's body and flourish. Death of the insect may take 3-5 days, but the dead insects may serve as a reservoir of spores for secondary spreading of the fungus. Insects can also disperse the fungus through mating. Relatively high humidity and availability of water enhance the growth of the conidia and the succeeding infection of the insect.
The features of bioinsecticide B bassiana are:
- Distinctive strain of B. bassiana can infect a wide array of insects; strains differ in their spectrum of hosts.
- The fungus grows faster and possesses high degree of specificity.
- The spores are able to remain for a long time with entomopathogenic ability.
- The action of the bioinsecticide are observed in 5-7 days after treatment.
- Highly effective within temperature of 25°-28°C and relative humidity of 80-90% and also by the methods and doses of application.
- In addition to infecting insects, B. bassiana can colonize corn plants, having the capability of living in the vascular tissue of certain corn cultivars (plant or grouping of plants selected for desirable characteristics that can be maintained by propagation) as an endophyte.
Impacts of Application of B bassiana
- On humans: studies indicate that there are no likely health risks to peoples who apply this insecticide or to people who consume the crops that have been treated with the fungus. Anyways precaution should be taken during application since they can be irritants to the eyes, skin and lungs.
- On wild species: It is non-toxic to mammals, plants and birds. However application of Beauveria to water is not preferred, as they are highly toxic to fish. Since this product is used to control a wide array of insect types, predators in these insect classes could also be affected. Precaution should be taken while applying it when honeybees are actively feeding.
Unreasonable selection and application of chemical pesticides led to environmental toxicity of their residues, decrease or loss of efficiency due to the evolution of pathogens, unwanted effects on non-target organisms sharing the ecosystem. Therefore one of the important ecological challenges scientists will face in the near future is the development of environmental friendly (biodegradable) alternatives to the widespread use of chemical pesticides for fighting crop diseases. The utilization of biological targeting of pests is measured as one of the most promising methods for more reasonable and safe crop management practices.
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