Bt toxins are insect-group specific. Different Bt (Cry) genes produce toxins effective against different insect pests. Therefore, the choice of Bt gene depends on:

(i) The crop in which the gene is to be introduced.

(ii) The targeted pest that attacks that crop.

For example:

Cry1Ac → Cotton bollworm (Lepidopteran)

Cry3A → Beetles (Coleopteran)

Hence, both the crop and the targeted pest determine the choice of Bt gene.

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