Spores and crystalline insecticidal proteins produced by B. thuringiensis are used as specific insecticides under trade names such as Dipel and Thuricide. Because of their specificity, these pesticides are regarded as environmentally friendly, with little or no effect on humans, wildlife, pollinators, and most other beneficial insects. The Belgian company Plant Genetic Systems was the first company (in 1985) to develop genetically engineered (tobacco) plants with insect tolerance by expressing cry genes from B. thuringiensis.
B. thurigiensis-based insecticides are often applied as liquid sprays on crop plants, where the insecticide must be ingested to be effective. It is thought that the solubilized toxins form pores in the midgut epithelium of susceptible larvae. Recent research has suggested that the midgut bacteria of susceptible larvae are required for B. thuringiensis insecticidal activity.
Bacillus thuringiensis serovar israelensis, a strain of B. thuringiensis is widely used as a larvicide against mosquito larvae, where it is also considered an environmentally friendly method of mosquito control.
Thus, B. thuringiensis serves as an important reservoir of Cry toxins and cry genes for production of biological insecticides and insect-resistant genetically modified crops. When insects ingest toxin crystals the alkaline pH of their digestive tract causes the toxin to become activated. It becomes inserted into the insect's gut cell membranes forming a pore resulting in swelling, cell lysis and eventually killing the insect.
The most celebrated problem ever associated with Bt crops was the claim that pollen from Bt maize could kill the monarch butterfly. This report was puzzling because the pollen from most maize hybrids contains much lower levels of Bt than the rest of the plant and led to multiple follow-up studies. In the end, it appears that the initial study was flawed; based on the way the pollen was collected, they collected and fed non-toxic pollen that was mixed with anther walls that did contain Bt toxin. The weight of the evidence is that Bt crops do not pose a risk to the monarch butterfly.
For More Information: Genetically Modified Organisms (GMOs)
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