What various methods do man use to control harmful insects?

The introduction of parasites, pathogens and predators is the method which is used in biological control.

Specifically, the term biological control indicates the use of animal- and plant-based organisms to deal with pests and the damages and diseases which they cause. The approach is in line with imitating what Mother Nature does in regard to problems. Parasites, pathogens and predators represent lethal stresses upon pests that are wearing away at herbaceous and woody plants.