as discovery declines and development costs increase (Ollinger and Fernandez-Cornejo, 1995).
Broad-spectrum insecticides that kill nontarget arthropods can exacerbate or even create new pest problems by eliminating biological control organisms that previously held the pests in check. For example, DeBach and Rosen (1991) described the elevation of the citrus red mite from a minor or nonpest status to the most important citrus pest in California following the introduction of chlorinated hydrocarbon and organophosphate pesticides. Similar increases in mite problems after the introduction of pesticides have been reported worldwide (Gerson and Cohen, 1989; Huffaker et al., 1969, 1970; McMurtry et al., 1970). Cottony-cushion scale emerged as a major pest in California's central valley after DDT caused large reductions in the populations of a biological control organism (DeBach and Rosen, 1991); brown soft scale became a major citrus pest in the Lower Rio Grande Valley in Texas in 1959 when parathion applied to adjacent cotton fields drifted into citrus groves and killed biological control organisms (Dean et al., 1983); and, outbreaks of citrus red mite, purple scale, and woolly whitefly followed large applications of carbaryl and chlordane in an attempt to eradicate the Japanese beetle (DeBach and Rose, 1977).
Diseases induced by, or made more severe after, the use of healing agents are termed "iatrogenic" disease; examples of iatrogenic plant diseases can be cited for all major groups of crop protection chemicals (Griffiths, 1993). Botrytis rot of cyclamen (caused by Botrytis cinerea) was initially well controlled by the fungicide benomyl, but it became much more severe when benomyl-resistant strains appeared. Prior to the use of benomyl, populations of B. cinerea were suppressed by antagonistic strains of Penicillium brevicompactum. Benomyl eliminated the P. brevicompactum, which was sensitive to the fungicide, so that when the benomyl-insensitive strain of B. cinerea appeared, it was more damaging to the host than it had been prior to the discovery of benomyl. Eventually, benomyl-insensitive strains of P. brevicompactum appeared, effectively returning the original balance of biological suppression (Griffiths, 1993).
Unjudicious use of broad-spectrum chemical pesticides for pest management has encouraged resistance in agricultural pests, increased secondary pest problems, increased the probability of dietary and occupational exposure to harmful chemicals, and produced adverse effects on soil and water resources and nontarget species.
For many pest problems, no conventional pesticide offers a feasible solution. Examples include problems caused by exotic pests (for which there are no indig-