Effects of atrazine on the toxicity, penetration and metabolism of carbofuran in the house fly.

Abstract

Experiments were conducted to obtain additional information relative to the effects of the herbicide atrazine on the toxicity, penetration, and metabolism of 14C-carbofuran in Musca domestica L. Topically applied carbofuran yielded, after 24h, an LD-50 at 0.16 μg/fly but dropped to 0.08 μg/fly when a nontoxic dose of 15 μg of atrazine also had been applied. In the presence of atrazine, twice as much 14C-carbofuran was left on the outside of the flies as compared to controls. Conversely, amounts of the less toxic metabolite 3-hydroxy-carbofuran in the chloroform extraction phase of fly excreta were only 30% of those excreted by control flies. Amounts of the major metabolite 3-hydroxycarbofuran in the water extraction phase of fly excreta were 2.57% of the applied radiocarbon after 14C-carbofuran plus atrazine treatment and 4.14% in excreta from control flies, thus indicating a reduction in the formation of this carbofuran metabolite due to atrazine. The respective figures were 0.38 and 0.97% for 3-hydroxycarbofuran phenol and 0.12 and 0.31% for carbofuran phenol. Data indicated that the herbicide atrazine inhibited the penetration of 14C-carbofuran into houseflies or stabilized it on the cuticle, thus making its biological activity available over longer time periods. In addition, it inhibited the metabolic detoxication of the insecticide into less insecticidal compounds, whose toxicity in turn also could be enhanced by atrazine. The increased stability of 14C-carbofuran, both outside and inside the insect body, resulted in an increased toxicity of the insecticide, thus explaining to some extent the synergism of carbofuran with atrazine in house flies.