An Advanced Method for Economic Threshold Determination: A Positive Approach

Economic entomologists have historically concerned themselves with reducing or preventing insect damage. These goals have led to the “economic threshold†concept used by entomologists to define a pest population level at which controls should be initiated (National Research Council, pp. 240). Stern (1966) defined it as “… the pest population density at which control measures should be determined to prevent an increasing population from reaching the economic injury level.†A serious attempt was made by J.C. Headley to define the economic threshold as the “ … population (of pests) that produces incremental damage equal to the cost of preventing that damage†(Headley, p. 105). Although logically sound, Headley's model, designed to quantify its definition, fails to treat the time dimension properly as shown in Hall and Norgaard's two-variable model (Hall and Norgaard, pp. 199-201). This two-variable model holds only under rather strong assumptions (Borosh and Talpaz, pp. 642-643), and a priori considers only a situation with a single pesticide treatment policy. A multiple treatment case was developed (Talpaz and Borosh, pp. 769-775) with equal physiological time intervals between treatments, which may apply to some special cases. An interesting effort to introduce increasing pest resistance was made by Hueth and Regev (pp. 543-555).