Biological control is the use of living beneficial organisms to combat pests. The following background information will help you better understand biological control of soybean aphid. Much of the following information is extracted or adapted from Biological Control of Insects and Mites: an introduction to beneficial natural enemies and their use in pest management, North Central Regional Extension Publication 481, published by University of Wisconsin-Extension.

A little history

The cottony cushion scale was a major pest of citrus in the 1880s. Efforts at controlling this pest with the vedalia beetle (below) resulted in one of the earliest and most impressive examples of biological control Photo credit: Jack Kelly Clark UC Statewide IPM Project

Many centuries ago, Chinese farmers observed that in their citrus orchards ants were providing natural control of insect pests by feeding on caterpillars, beetles, and leaf-feeding bugs. The farmers discovered that collecting the papery nests of a specific type of ant from trees in the countryside and moving them into their orchards improved control of some orchard pests. They also provided aerial bamboo runways among the citrus trees to help the ants move easily from tree to tree.

These efforts to increase the numbers of ants in the orchard and to heighten their efficiency as predators are the first recorded occurrence of biological control of insects, which is the intentional manipulation of populations of living beneficial organisms, called natural enemies, in order to limit populations of pest insects.

In the mid-1880s, southern California's developing citrus industry experienced devastating losses from an introduced pest, cottony cushion scale. Growers tried every available chemical control, even fumigation with hydrogen cyanide, but nothing provided sufficient control; many growers removed their citrus groves because the damage was so serious.

After determining that the scale insect was native to Australia and New Zealand, the United States Department of Agriculture sent an entomologist to that area to look for effective natural enemies. The entomologist found a small lady beetle, the vedalia beetle, which he sent to California. It rapidly reproduced in infested citrus groves and brought the cottony cushion scale under complete and lasting control. This was the first highly successful case of controlling an alien pest by introducing its natural enemies from their native land, a technique now known as importation or classical biological control.