The Effectiveness of Chlorinated Hydrocarbon Insecticide Mixtures for Control of Resistant and Susceptible Boll Weevils1

Abstract

The toxicity of toxaphene and DDT alone and combined in various proportions on laboratory-reared toxaphene resistant and susceptible strains of the boll weevil was studied, Toxaphene-DDT mixtures exhibited synergistic effects on resistant weevils, but only additive effects for susceptible ones. A mixture of four parts toxaphene and one part DDT was the most effective combination tested against resistant weevils. A dosage of 5 to 15 micrograms of toxaphene in combination with DDT was required to produce 50% mortality of resistant weevils regardless of the amount of DDT in the combination. No evidence of synergism was found using mixtures of toxaphene with methoxychlor or DDE. A mixture of Strobane-DDT was slightly less effective than toxaphene-DDT, but the synergistic effect was evident with resistant weevils. Strobane® is a mixture of chlorinated terphenes with about 66% of chlorine. No evidence was found of seasonal tolerance in field-collected boll weevils to a 2-1 mixture of toxaphene-DDT.