wheat, a major crop with the second largest acreage in the United States, account for only 3.5 percent of the total (Lin et al., 1995).

INTEGRATED PEST MANAGEMENT

Integrated pest management (IPM) was intended to put pesticide use on a more sound ecological footing. Stern and colleagues (1959) introduced the term integrated control and defined it as "applied pest control which combines and integrates biological and chemical control. Chemical control is used as necessary and in a manner which is least disruptive to biological control" (p. 86). Pest management was to be based on the naturally occurring regulatory processes in the agroecosystem that help prevent pest outbreaks.

Stern and colleagues (1959) suggested that pests should be reduced (as opposed to completely exterminated) only when their populations reach levels at which economic injury to the crop is expected, thus also introducing the concepts of economic-injury level and economic threshold to guide decisions about when and whether pest populations should be reduced. Economic-injury level is determined by measuring the effect on the crop plant and the damage it can tolerate. Economic threshold, set below the economic-injury level, serves to signal the need for action to keep the pest population from reaching the point at which economic injury would occur.

The founding principles of IPM are that natural processes can be manipulated to increase their effectiveness, and chemical controls should be used only when and where natural processes of control fail to keep pests below economic-injury levels. These principles were refined, expanded, and incorporated into many of the concepts of pest management advocated by others (Doutt and Smith, 1971; National Research Council, 1969; Rabb and Guthrie, 1972; Smith, 1969; Smith and van den Bosch, 1967; U.N. Food and Agriculture Organization, 1967). Similar concepts and definitions of pest management were used as the basis for accelerating adoption of national agricultural initiatives during the administrations of presidents Nixon (Council on Environmental Quality, 1972) and Carter (Bottrell, 1979).

IPM in its original sense of integrated control or ecologically based management, however, has not been implemented on a wide scale (Cate and Hinkle, 1993; Flint and van den Bosch, 1981; Hoy and Herzog, 1985; Kogan, 1986). Critics argue that the most widely used IPM strategies stress improved pesticide usage based on monitoring pest populations and setting economic thresholds (Fitzner, 1993). Many scientists have noted that IPM strategies normally depend on pesticides as the primary management tool and have highlighted the need to develop systems that depend primarily on biological control organisms, resistant plants, cultural controls, and other ecologically based tools (Cate and Hinkle, 1993; Edwards, 1991; Ferro, 1993; Flint and van den Bosch, 1981; Frisbie et al., 1992; Frisbie and Smith, 1989; Hoy and Herzog, 1985; Kogan, 1986; Pedigo and



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