Rate of Population Increase of the Twospotted Spider Mite (Acari: Tetranychidae) on Peanut Leaves Treated with Pesticides1

Abstract

Several commonly used pesticides were evaluated for their effect on the intrinsic rate of natural increase (r_m) of Tetranychus urticae Koch on peanut to determine whether or not stimulation of mite reproductive potential by pesticides was a factor contributing to mite population increases in peanut fields. Mites fed on peanut leaves treated with mancozeb, carbaryl, and mancozeb + carbaryl had slightly, but consistently, higher r_m values than mites fed on leaves from the nontreated check. Mites exposed to peanut leaves treated with ammonical copper, fentin hydroxide, benomyl, and benomyl + mancozeb + carbaryl had slightly, but consistently, lower r_m values than mites exposed to the nontreated check. The data suggest that some pesticides can contribute to increased mite populations in peanut fields by stimulation of the mite’s reproductive potential, whereas other pesticides suppress mites by reduction of mite reproductive potential. Two spotted spider mites on peanut leaves exhibited a greater reproductive potential than reports in the literature for other plants. Therefore, when pesticides reduce the factors limiting populations on peanut, this reproductive potential may result in mite population increases.