Bacillus thuringiensis (Bt) and its insecticidal toxins have been used in agronomical pest control for decades. The mechanism of action of Bt toxins on insect pest involves specific molecular interactions which makes Bt a popular choice for pest control. The specificity of action of Bt toxins reduces the concern of adverse effects on non-target species, a concern which remains with chemical insecticides. Different strains of Bt are known to express different classes of toxins which in turn target different insects. Bt and its toxins can be formulated into powder or liquid sprays or expressed in transgenic plants. To maximize the effect of Bt toxins, multiple toxins are often combined when making Bt formulations or expressed in transgenic plants. Though Bt is a very effective biological control agent, there are concerns over the development of resistance by insect species and also the narrow spectrum of activity of individual toxins. To address these concerns, new strains of Bt expressing novel toxins are actively sought and existing toxins are genetically modified for improved activity.

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