The insect and mite control potential of natural and biological toxins has been recognized for several centuries. Bacteria, viruses, protozoa and fungi are the primary groups of microorganisms known to reduce insect populations; they often occur naturally in fields and function as components of biological control. Beneficial nematodes are also being used for pest control, especially against soil insects. The isolation of toxic metabolic compounds from microorganisms continues to be a fruitful research area, although there are barriers to their successful marketing and distribution. Another, more controversial way to deliver these insect-specific toxins to the target pest is through genetically modified plants, such as those modified to express Bacillus thuringiensis (Bt) toxins. Oils and particle films also have important niche uses for pest control.