Why should biological control of pests and pathogens be preferred to the conventional use of chemical pesticides?

Explanation

(a) Bacillus thuringiensis-Bacillus thuringiensis is a bacterium. B-toxin gene is cloned from bacterium and expressed in plants to provide resistance from insect without using insecticides. Thus, by the application of biotechnology pest resistant plant are developed. Some other examples are Bt corn, Bt ricé, Bt tomato, Potato and Soyabean.
When they are eaten by the insect larvae, the toxin is released in the gut and becomes active and kills the larvae. Specific Bt toxin genes obtained from Bacillus thuringiensis are used in several crop plants which make them resistant to the insect Pest.
(b) Nucleopolyhedrovirus-These viruses are excellent candidates for species speciiic, narrow spectrum insecticidal applications.
They have been shown to have no negative impacts on plants mammals, birds, fish or even I on non-target insects. They are especially desirable when beneficial insects are being conserved r to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.