Why are biological control methods adopted in agricultural pest control? 

Biological pest control use the natural enemies of pests to kill or reduce their impact. Though biological controls may not completely eradicate a pest but they offer high advantages over other control methods, Such as:

1. Biological pest control creates no chemical run off in water or soil. Therefore no possibilities for water pollution, imbalance in the soil contents, ground water pollution.
2. They are very target specific. Biological control targets a very narrow range of pests, sometimes only a single species. So the control used for a particular pest mostly does not cause any harm to the other benefical organimsm living in the same area.
3. This is a highly cost effective practice.
4. If a biological control measure is established successfully, the species will remain stable population for generations without need for additional investments by human.