A pesticide is a chemical used to control, to repel, to attract or to kill pests, for example, insects, weeds, birds, mammals, fish, or microbes, considered a nuisance.
Chemical engineers develop new pesticides continually as insects grow resistant to older chemicals with steady
use, requiring ever increasing dosages.
DDT is an example of a heavily used and misused pesticide.
Gene engineering plants (corn) to create and emit their
own pesticides has become controversial with revelations
of gene engineered corn contaminating U.S. food supplies
in late 90s.
See also herbicide -- DDT