Toxicokinetic Analysis, of Dermally Applied Diazinon in Resistant and Susceptible Houseflies, Musca domestica L.

Abstract

Toxicokinetic analysis was employed to investigate significance of various factors responsible for resistance in susceptible and resistant strains of housefly to diazinon. Topical application and application by exposure to a residual film of the compound in holding vial was conducted. A significant difference was observed between the strains in the penetration rate of diazinon, the amount of diazoxon present, and the degree of AChE inhibition. the data also indicated a reversible exchange of diazinon between external surface of the flies and the holding vial by volatilization/rub-off and resorption of the compound by the flies. Certain k values estimated by computer simulation using the experimental data and differential equations derived from the toxicokinetic models proposed for the external and internal dynamics of diazinon demonstrated an inter-strain difference. In particular, the ratio of diazoxon degradation over activation of diazinon was much greater in the resistant strain than in the susceptible strain, suggesting that low accumulation of diazoxon was the most important resistance factor. Insensitive AChE also played an important role in vivo.