Approaches to biological control

Biological control is one of several general approaches to insect control. The intent of biological control is not to eradicate pests, but to keep them at tolerable levels where they are not causing appreciable harm. In fact, because natural enemies require their prey or hosts for survival, biological control works best when there is always a small population of pests on which to feed. This is a major difference between biological control and the use of pesticides.

Aphid mummies (parasitized aphids) on a leaf. Photo credit: Bob Ellingson

There are three broad approaches to biological control. Importation of natural enemies (also called classical biological control) is conducted by federal and state agencies to find better beneficial natural enemies and permanently establish them into new areas. It is this approach that is being researched in the current soybean aphid biological control project. Collaborating scientists have traveled to various parts of Asia looking for better natural enemies of soybean aphid.

Conservation of natural enemies improves the effectiveness of natural enemies through farming and gardening practices that provide necessary resources for their survival and protect them from toxins and other adverse conditions. Once effective natural enemies of soybean aphid have been identified, it is important not to interfere with their activities or else their impact will be less than desired. For example, broad spectrum insecticides are very hard on natural enemies and should not be used unless absolutely necessary. Crops should be scouted and pesticides applied only when pests reach economic thresholds. If possible, use selective insecticides or treat only those areas where pests are exceeding treatment thresholds.

Augmentation of natural enemies temporarily increases the numbers of natural enemies through periodic releases, thereby increasing the overall numbers of natural enemies and improving biological control. About 125 different types of natural enemies are currently available for purchase in North America. Because of costs, augmentation biological control tends to be used more frequently on higher value horticultural crops.