Prevention is always better than cure. Plants are harmed if attacked by pests. Preventive measures and biological control methods are preferred for protecting crop plants, because they not only prevent the stored food materials from getting, spoiled, getting infested by insects, bacteria and micro-organisms. These methods also protect crops from chemicals which are sometimes added, to control the pests attacking stored food grains. These chemicals are toxic. Some pesticides lead to biomagnification. Biological methods are eco-friendly too.