Bacillus thuringiensis
Bacillus thuringiensis (B.t.) is a naturally occurring bacterium that serves as a microbial pesticide, offering an alternative to traditional chemical pesticides in agricultural pest control. It produces a specific proteinaceous crystal that is harmless until ingested by certain target insects, where it becomes toxic due to activation in the insect’s digestive system. This targeted approach allows B.t. to effectively manage pest populations, such as mosquitoes and caterpillars, without adversely affecting beneficial insects or the environment. Commercial use of B.t. began in the 1960s, with its popularity growing as awareness of environmental pollution from chemical pesticides increased. Various strains of B.t. have been developed to combat over 150 different insect species, making it a versatile tool in integrated pest management. Additionally, advances in genetic engineering have explored introducing B.t. genes into plant genomes, potentially creating crops that are resistant to pests without the need for external applications. However, such methods raise debates around the safety and ethics of genetically modified organisms (GMOs). Overall, B.t. represents a promising approach to sustainable agriculture, balancing pest control with ecological considerations.
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Bacillus thuringiensis
DEFINITION: Natural microbial pesticide used for biological control of insects
Bacillus thuringiensis provides an environmentally neutral alternative to chemical pesticides, which can leave pollutants in soil and water.
Chemical control of plant parasites using pesticides, while often effective, has generally been found to create its own problems in areas of environmental pollution. The use of microbial pesticides has often proven as effective at pest management, without the problems of polluting soil and water. In addition, since many of these organisms are species-specific, targeting only select insects, neither plants nor more desirable insects (such as ladybugs) are at risk.
Bacillus thuringiensis (B.t.) is one of several bacteria species that have been used as biopesticides for control of insects. The bacterium produces a proteinaceous parasporal crystal within the cell when it sporulates (that is, forms spores) that is toxic only for a specific insect host. The crystalline protein is harmless in its natural state, becoming toxic only when it is cleaved by specific proteases. Once the bacterium has been ingested by the target insect, the alkaline secretions within the midgut of the insect activate the toxic character of the crystalline body. The toxin binds the intestinal cells, resulting in formation of pores and leakage of nutrients from the gut, and the insect dies within three to five days. The ability of the bacterium to sporulate also provides a means to disseminate the organism as a spray. Some commercial treatments utilize the crystalline body itself, which is sprayed onto the plants.
Though commercial application of B.t. began in the 1960s, widespread use began only decades later with the decline in use of chemical pesticides for protecting food crops and other types of plants. Various strains of B.t. have been developed for use against numerous types of insects. The israelensis variety is used commercially for control of mosquitos and blackfly larvae. The variety kurstaki has been used effectively against both the gypsy moth and cabbage loopers. More recently developed strains of B.t. have been shown to be effective in controlling insects that feed on fruit crops such as oranges and grapes. Varieties of B.t. are used commercially against some 150 different insect species, including cabbage worms, caterpillars, and other insects that feed on vegetable crops. The targeting of specific insects while using certain strains of B.t. also reduces the chance that desirable populations of organisms may be adversely affected.
Attempts have also been made through genetic engineering to introduce the gene that encodes the crystalline body directly into the plant genome. Since the protein is toxic only to insects, such an approach may result in naturally insect-resistant plants without further need for spraying. The procedure has proven effective in controlled experiments using tobacco plants, and more widespread testing in other plants has also been undertaken. The controversial nature of introducing such potentially toxic genes may preclude their use in food crops for some time, but such genetic experiments may prove useful in natural protection of ornamental trees and other plants.
Bibliography
"Bacillus Thuringiensis (Bt) Fact Sheet." National Pesticide Information Center, May 2022, npic.orst.edu/factsheets/btgen.html. Accessed 15 July 2024.
Letourneau, Deborah K., and Beth Elpern Burrows, eds. Genetically Engineered Organisms: Assessing Environmental and Human Health Effects. Boca Raton: CRC, 2002. Print.
Metz, Matthew, ed. Bacillus Thuringiensis: A Cornerstone of Modern Agriculture. Binghamton: Haworth , 2003. Print.