We generally do not consider introducing exotic natural enemies against native plants and insects, no matter how much we may dislike them. Native species have evolved in our ecosystems and may play important, if unappreciated and little understood roles, now or in the future. Besides, there is no shortage of exotic pests to work on. There are about 1,700 introduced insects in this country and more than half of them are identified as pests. Work on biological control generally begins in the homeland of the invasive pest.
Purple loosestrife is a good example .
This attractive purple-flowered plant was accidentally introduced into the United States in ship's ballast two centuries ago. Subsequently, it has been purposely introduced and distributed as a garden plant. With no insect natural enemies, loosestrife has spread throughout much of North America's wetlands, displacing native plants and animals in the process. This plant is widespread but relatively uncommon throughout its European homeland where 120 species of insects feed on it. Once a program is initiated, it takes several years of careful research before a biocontrol agent is introduced against an invasive plant.