How effective is biological control?
Biological control has been practiced in the US for over 100 years with both successes and failures. In this country, most of the effort has gone into the control of insect pests. Farmers in Michigan are very familiar with the highly successful control of two exotic insect pests, the cereal leaf beetle and the alfalfa weevil, using parasites imported from Europe. The alfalfa weevil project is estimated to save US agricultural producers $10 million per year in reduced pesticide usage and increased yields. Control of Klamath weed, another European invader of rangelands in the western US was also highly successful in just a few years. However, in other cases natural enemies have failed to establish or never built-up to sufficient numbers to impact the pest. Fortunately, in the case of purple loosestrife, some of these hurdles have already been overcome.
