[3] During sporulation, many Bt strains produce crystal proteins (proteinaceous inclusions), called delta endotoxins, that have insecticidal action.

[7] As a toxic mechanism, cry proteins bind to specific receptors on the membranes of mid-gut (epithelial) cells of the targeted pests, resulting in their rupture.

[11] In 1911, German microbiologist Ernst Berliner rediscovered it when he isolated it as the cause of a disease called Schlaffsucht in flour moth caterpillars in Thuringia (hence the specific name thuringiensis, "Thuringian").

[14][15] B. thuringiensis is closely related to B. cereus, a soil bacterium, and B. anthracis, the cause of anthrax; the three organisms differ mainly in their plasmids.

The insect parasite Btk HD73 carries a pXO2-like plasmid (pBT9727) lacking the 35kb pathogenicity island of pXO2 itself, and in fact having no identifiable virulence factors.

[18] Common with B. cereus but so far not found elsewhere – including in other members of the species group – are the efflux pump BC3663, the N-acyl-L-amino-acid amidohydrolase BC3664, and the methyl-accepting chemotaxis protein BC5034.

[23] Cry toxins have specific activities against insect species of the orders Lepidoptera (moths and butterflies), Diptera (flies and mosquitoes), Coleoptera (beetles) and Hymenoptera (wasps, bees, ants and sawflies), as well as against nematodes.

Thus, B. thuringiensis serves as an important reservoir of Cry toxins for production of biological insecticides and insect-resistant genetically modified crops.

[24] The Cry toxin is then inserted into the insect gut cell membrane, paralyzing the digestive tract and forming a pore.

[38] Spores and crystalline insecticidal proteins produced by B. thuringiensis have been used to control insect pests since the 1920s and are often applied as liquid sprays.

[67] The use of Bt toxins as plant-incorporated protectants prompted the need for extensive evaluation of their safety for use in foods and potential unintended impacts on the environment.

[68] Concerns over the safety of consumption of genetically modified plant materials that contain Cry proteins have been addressed in extensive dietary risk assessment studies.

As a toxic mechanism, cry proteins bind to specific receptors on the membranes of mid-gut (epithelial) cells of the targeted pests, resulting in their rupture.

While the target pests are exposed to the toxins primarily through leaf and stalk material, Cry proteins are also expressed in other parts of the plant, including trace amounts in maize kernels which are ultimately consumed by both humans and animals.

The United States Environmental Protection Agency recognizes mouse acute oral feeding studies where doses as high as 5,000 mg/kg body weight resulted in no observed adverse effects.

[71] The results of toxicology studies are further strengthened by the lack of observed toxicity from decades of use of B. thuringiensis and its crystalline proteins as an insecticidal spray.

[73] Additionally, skin prick testing using purified Bt protein resulted in no detectable production of toxin-specific IgE antibodies, even in atopic patients.

[76] Concerns over possible environmental impact from accumulation of Bt toxins from plant tissues, pollen dispersal, and direct secretion from roots have been investigated.

[77][78][79] Bt toxins are less likely to accumulate in bodies of water, but pollen shed or soil runoff may deposit them in an aquatic ecosystem.

[80] The toxic nature of Bt proteins has an adverse impact on many major crop pests, but some ecological risk assessments has been conducted to ensure safety of beneficial non-target organisms that may come into contact with the toxins.

[83] Bollworm resistance to first-generation Bt cotton was also identified in Australia, China, Spain, and the United States.

[85] Additionally, resistance to Bt was documented in field population of diamondback moth in Hawaii, the continental US, and Asia.

[91] Another study in five provinces in China found the reduction in pesticide use in Bt cotton cultivars is significantly lower than that reported in research elsewhere, consistent with the hypothesis suggested by recent studies that more pesticide sprayings are needed over time to control emerging secondary pests, such as aphids, spider mites, and lygus bugs.

[92] Similar problems have been reported in India, with both mealy bugs[93][94] and aphids[95] although a survey of small Indian farms between 2002 and 2008 concluded Bt cotton adoption has led to higher yields and lower pesticide use, decreasing over time.

"[99][100][101][102] Similarly, B. thuringiensis has been widely used for controlling Spodoptera littoralis larvae growth due to their detrimental pest activities in Africa and Southern Europe.

[108] One study found small-scale (about 1%) introduction of transgenic sequences in sampled fields in Mexico; it did not find evidence for or against this introduced genetic material being inherited by the next generation of plants.

"[111] As of 2007, a new phenomenon called colony collapse disorder (CCD) began affecting bee hives all over North America.

[113] The Mid-Atlantic Apiculture Research and Extension Consortium found no evidence that pollen from Bt crops is adversely affecting bees.

[116] Some isolates of B. thuringiensis produce a class of insecticidal small molecules called beta-exotoxin, the common name for which is thuringiensin.

[117] A consensus document produced by the OECD says: "Beta-exotoxins are known to be toxic to humans and almost all other forms of life and its presence is prohibited in B. thuringiensis microbial products".