Biological control is the use of living organisms, either native or introduced, to suppress pests below levels of serious economic or aesthetic damage. There are three general strategies employed in biological control: conservation, augmentation, and introduction (classical biological control).

• Conservation is protecting and enhancing the biological control agents that are already present. To protect naturally occurring biocontrol populations, avoid unnecessary spraying and broad-spectrum pesticides. One conservation practice is to use selective pesticides. One such material is the bacterial insecticide Bacillus thuringiensis, which now comes in various strains to control true caterpillars, certain mosquitoes, and leaf-feeding beetles. This material kills only target pests and has no direct effect on bees or other beneficial creatures.
  
• Augmentation adds to the established base of beneficials or restores a decimated population. This method is becoming more popular both on the homefront and in commercial operations. Green lacewings and predatory mites can be purchased to control aphids and spider mites, respectively. Insect-eating nematodes are now commercially available and can manage pests such as root weevils. When using these beneficial agents, it is critical to pay attention to criteria for successful release (e.g., time of release, weather conditions, and food availability).

  Some beneficials are not good candidates for release on small tracts of land. Lady beetles, for example, are genetically programmed to disperse after hibernation before they will settle down, mate, and lay eggs. Since lady beetles are normally collected during hibernation and sold before dispersal flight occurs, the purchaser is usually chagrined by disappearance of their flock often occurring one day after being released. Research is being done on how to keep them from leaving the release site. There are lists of suppliers of beneficial organisms available and extension entomologists can provide these upon request.

• Introduction or classical biocontrol is normally carried out by government agencies for a variety of reasons. Private citizens are not usually involved because of prohibitive costs. However, they might be involved in some programs relative to weed control. One example is the cinnabar moth and tansy ragwort--a noxious weed that the cinnabar moth larvae relish. Private citizens helped release and protect this insect in cooperation with county weed boards and university research programs. There is one concern about this insect to be aware of--the ornamental dusty miller is in the same genus as tansy ragwort and the caterpillars will feed on it readily.

  Another form of biocontrol emerging as a success story is peculiar to certain plant diseases. The control takes place through competitive exclusion. A notable example is the control of crown gall (Agrobacterium tumefaciens) by using noninfective A. radiobacter in advance of infection. Infection sites are locked up by the noninfective bacterial strain preventing establishment of the infective strain.

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