BEHAVIORALLY ACTIVE COMPOUNDS MAY NOT ENHANCE PESTICIDE TOXICITY - THE CASE OF DICOFOL AND AMITRAZ

A behaviorally active formamidine pesticide was used to test the hypot hesis that efficacy of the chlorinate;l hydrocarban acaricide, dicofol , could be increased by enhancing pest locomotion or decreasing pest a voidance of dicofol, or both, on treated leaves. Amitraz, dicofol, and mixtures of amitraz + dicofol were sprayed on plants in a manner that created discontinuous, checker-board residues. Behavior and mortality of twospotted spider mites, Tetranychus urticae Koch, were then obser ved. Evaluated alone, or in mixture with dicofol, amitraz resulted in significant increases in mite locomotion and. in mixtures with dicofol , eliminated mite avoidance of dicofol residues. Though both of the de sired behavioral modifications were achieved, the toxicity of amitraz + dicofol was actually less than that of dicofol alone, as revealed by probit analyses of 72-h discontinuous residue bioassays. Hypotheses f ormulated to explain this toxicologically undesirable outcome of the m ixture of dicofol and the behaviorally active compound were decreased alimentary uptake of toxicant or antagonistic chemical or physiologica l interactions between dicofol and amitraz. Our findings warn of the p otential for unexpected and detrimental outcomes of the use of behavio rally active chemicals to enhance toxicity of conventional pesticides. Even for chemicals like formamidines, that strongly influence pest be havior, the benefits of chemical mixtures should be demonstrated empir ically in the laboratory and field before being recommended for pest m anagement.