What is meant by the term bio-pesticide? Name and explain the mode of action of a popular biopesticide.

(N/A) bio-pesticide is a type of pesticide that is $(a)$ biological in origin rather than synthetic chemical,$(b)$ highly specific in its action against target pests,and $(c)$ environmentally safer compared to conventional chemical pesticides.
$A$ widely used bio-pesticide is the $Bt$ toxin,which is produced by the bacterium $Bacillus$ $thuringiensis$. The gene encoding $Bt$ toxin has been cloned and expressed in various crops. When an insect ingests the $Bt$ toxin protein,the alkaline $pH$ of the insect's gut converts the protoxin into its active form. This activated toxin binds to the surface of the midgut epithelial cells,creating pores that cause cell swelling and lysis,eventually leading to the death of the insect.