Shigeki Tashiro

Metabolism of PyracDofos in Housefly, Musca domestica

Abstract In vivo metabolism of pyraclofos, (R, S)- [0-1-(4-chlorophenyl) pyrazol-4-yl O-ethyl S- n -propyl phosphorothioate], labeled with 14 C on the benzene ring was studied in the housefly, Musca domestica. The metabolism of pyraclofos produced five main metabolites: EHP-CHP {1-(4-chlorophenyl) pyrazol-4-yl O-ethyl hydrogen phosphate}, formed by the cleavage of the n-propyl-S-P bond after oxidation of the S atom, CHP {1-(4-chlorophenyl)-4-hydroxy-pyrazole}, formed from cleavage of the P-O-aryl bond, CHP-sulfate, formed from the sulfate conjugate of CHP, CHP-glucose, formed from the glucose conjugate of CHP, and SHP-CHP {1-(4-chlorophenyl) pyrazol-4-yl S-n propyl hydrogen phosphorothioate}, formed from the cleavage of the P-O-ethyl bond. The proposed metabolic pathways of pyraclofos in the housefly are: cleavage of the P-O-aryl bond resulting in CHP and its conjugates, and cleavage of the P-S-n-propyl bond after oxidation of the sulfur atom resulting in EHP-CHP.

Reduced Penetration Rate of Pyraclofos into Housefly, Musca domestica, as a Resistance Mechanism

Abstract Ethylacetate was found to be suitable for washing pyraclofos from the insect body in experiments to determine the role of the cuticle in the penetration of pyraclofos into the body, and was recommended as a favorable solvent to study housefly resistance to pyraclofos. Three ml of ethylacetate washed off 99% of pyraclofos from the housefly body surface. The penetration through integument played an important role in resistance mechanism of the housefly to pyraclofos. There were considerable differences in penetration rate, excretion rate, and metabolism of the insect body between the resistant (YBOL) and susceptible (SRS) strains of housefly. In penetration study, the YBOL (resistant) strain showed a slightly greater inhibition of penetration than the SRS strain during 1 h after treatment at both the 8, 000-dpm and 4, 000-dpm treatments. Therefore, the reduced penetration rate of pyraclofos is one of the resistance mechanisms in the YBOL strain of housefly even though there were no significant differences of radioactivity between the YBOL and SRS strains after 2 h. For both 8, 000-dpm and 4, 000-dpm treatments, radioactivity in the YBOL surface extract was somewhat higher than in that of SRS, while radioactivity in the housefly body of SRS was higher than that of YBOL. Excretion rate was faster in the resistant housefly. This suggests that metabolic process might be also one of the resistance mechanisms of housefly to pyraclofos.