Demographic Toxicology as a Method for Studying the Dicofol-Twospotted Spider Mite (Acari: Tetranychidae) System

Laboratory experiments were conducted to examine the effects of dicofol on Tetranychus urticae Koch on a population basis. Age-specific survivorship, fecundity, and intrinsic rate of increase (r) were inversely related to dosage of dicofol, whereas developmental time was directly related to concentration of the compound. As the dosage of dicofol was increased, the stable age distribution shifted from a young and growing population to an old and declining population. Demographic toxicology may be of value in providing an alternative to the more conventional method of assessing pesticide efficacy. It shifts the emphasis and extends the scope of pesticide studies from that of measuring a single and static quantity (LD50) to that of measuring other life history traits and incorporating them into a more dynamic and multidimensional parameter (intrinsic rate of increase).