Bacillus thuringiensis is a Gram-positive, soil dwelling bacterium of the genus Bacillus. Additionaly, B. thuringiensis also occurs naturally in the caterpillars of some moths and butterflies, as well as on the surface of plants.

B. thuringiensis was discovered 1901 in Japan and 1911 in Germany by Ernst Berliner, who discovered a disease called Schlafsucht in flour moth caterpillars. B. thuringiensis is closely related to B. cereus, a soil bacterium, and B. anthracis, the cause of anthrax: the three organisms only differ in their plasmids. Like other members of the genus, all three are aerobes capable of producing endospores.

Use in pest control

Spores of B. thuringiensis, as well as proteins created by the organism are used as Lepidopteran-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 material is distributed, usually in a liquid spray on the leaves of affected plants, where the pesticide must be eaten to be effective. The protein crystals break down cells within the gut of the caterpillars. They stop feeding within minutes after ingestion and soon die.

Bacillus thuringiensis var israelensis, a strain of B. thuringiensis is widely used as a larvicide against mosquito larvae, where it is also considered an environmentally friendly technique of mosquito control.

Genetic engineering for pest control

Bacillus thuringiensis, or Bt, is an endospore forming, soil-dwelling bacterium. The bacteria forms protein crystal δ-endotoxins from Cry genes. These toxins have effects on Leidoptera (Caterpillars) and Coleptera (Beetles) species. These toxins are used as biological control in organic farming and as transgenes in GM crops.

Usage In 2000 more than 115,000 square kilometres of Bt transgenic crops were grown, constituting 19% of the worlds GM crops. There is potential for Bt GM crops to take up 33% of the insecticide market. The current use of transgenic Bt crops reduces the number of chemical insecticide treatments by more than 7.7 million acres (31,000 km²) per year.

Advantages Transgenic Bt crops have even distribution of the toxin throughout the plant. The treatment is constant unlike chemical spraying which creates many pauses.

Safety Transgenic crops, including Bt crops, are safe for the farmers and for consumers. The toxin is insect specific and poses no danger to humans or other vertebrates.

Problems The expression of the Bt gene can vary. For instance, if the temperature is not ideal this stress can lower the toxin production and make the plant more susceptible. Secondary pests are not controlled by Bt transgenic crops. Due to the constant exposure to the toxin an evolutionary selective pressure is created for resistant pests. There is a hypothetic risk that for example, transgenic maize will crossbreed with wild grass variants, en that the Bt-gen will end up in a natural evironment, retaining its toxicity.

Fighting Resistance Non-Bt-Gm crop refuges could be created to allow some non-resistant insects to survive and maintain a susceptible population. Moderate expression of the transgene would also achieve the same end. Creating a mosaic GM crop expressing many different Bt toxins would have a greater chance of eliminating the entire pest population.

Bt, Corn and Monarch Butterflies

The European Corn Borer is an economically significant pest of corn in the USA. This pest damages the stalks of corn plants in its second generation. A variant of Bt toxin, known as Kurstaki HD-1, has insecticidal effects on the Corn Borer. The gene for this variant, CrylA(b), has been transformed into corn plants creating a resistant GM strain of corn. This strain has been crossed with commercial corn strains to create economical, resistant strains. The levels of Bt toxin in these strains is low, but enough to kill the pest. The toxin causes no harm to other organisms or the crop.

Research was conducted to find the effect of this Gm Bt Crop on monarch butterflies which feed on milk-weed which grows at the edge of corn fields. The research included an experiment in which the butterflies were given milkweed dusted with the toxin as a food source. The experiment showed that the toxin had strong effects on the butterflies. This result was published in Nature as well as in many newspapers and there was public outrage at the risk presented to the endangered and endearing insects.

The scientific community took a different approach. As soon as the research was published it was immediately criticized. The experiment in which milkweed was dusted with Bt toxin did not reflect the real doses of Bt which would be received by milkweed bordering GM crops. Also, it was shown that Monarch butterflies, when given a choice, would not choose to eat dusted plants. The results of the research were debunked. The popular press took no note of the findings against the first research. This is one reason why public opinion of Bt GM crops and GM crops in general is so low.

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