Metabolism of Coumaphos in Susceptible and Resistant Strains of Boophilus microplus (Acari: Ixodidae)

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Abstract
A study was made of the comparative fate of [14C]coumaphos in larvae and adults of coumaphos-resistant (R) and -susceptible (S) strains of Boophilus microplus (Canestrini) that originated in Mexico. There were no differences between R and S strains in rates of cuticular penetration or internal accumulation of radioactive material after topical treatments (0.05 μg/tick) of unengorged adult females or after drench treatments (1 ppm) of larvae. Radioactive products of the metabolism of [14C]coumaphos in both larval and adult stages included the toxic oxygen analog (coroxon) and free and conjugated forms of chlorferon, the nontoxic substituted-coumarin ring moiety of the molecule. The rate of metabolic detoxification of absorbed coumaphos was more rapid in larvae than in adults of both strains. Concentrations of detoxification products were significantly lower, and of coumaphos and coroxon higher, in both larvae and adults from the susceptible strain. However, the levels of enhanced metabolic detoxification in R ticks appeared insufficient to account for all of the reported substantial (ca. 32–38 ×) differences between S and R strains in susceptibility to coumaphos.

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