Metabolism of Coumaphos in Larvae of the Cattle Tick Boophilus Microplus

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Strains of the cattle tick resistant to organophosphorus compounds were first found at Ridgelands in central Queensland in 1963 (Shaw and Malcolm 1964; Shaw 1966; Roulston, Stone, Wilson, and White 1968). Resistance of a different type was subsequently found at Biarra in south-eastern Queensland in 1966 (Roulston and Wharton 1967; Wharton 1967; Shaw, Cook, and Carson 1968). Ridgelands and Biarra strains of ticks both exhibit resistance to a wide range of organophosphorus and carbamate chemicals but differ in that resistance levels are higher and resistance extends to a wider range of chemicals in the Biarra strain. Biochemical investigations have shown that resistance in both strains is due to the presence of an acetylcholin-esterase system which is relatively insensitive to inhibition by organophosphorus chemicals (Lee and Batham 1966; Roulston, Schnitzerling, and Schuntner 1968; Schuntner, Roulston, and Schnitzerling 1968)

Section: Resultsmentioning

confidence: 99%

Detoxification as a Mechanism of Resistance I a Strain of the Cattle Tick Boophilus Micropluse (Canestrini) Resistant to Organophosphorus and Carbamate Compounds

Roulston¹,

Schuntner²,

Schnitzerling³

et al. 1969

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“…1971) of the method of Stone and Haydock (1962) was used in which larvae were confined in filter paper packets impregnated with olive oil containing the acaricides. In the latter technique larvae were dipped in aqueous suspensions of the acaricides as described by Roulston et al (1966). After dipping, the wet masses of larvae were partially dried on cotton wool balls.…”

Section: Acaricidal Treatment Of Larvaementioning

confidence: 99%

“…External and internal radioactive compounds were extracted by methods previously described (Roulston et al 1966), the former being determined by counting in a Packard Tri-Carb liquid scintillation spectrometer. The rate of penetration conformed very closely to first-order reaction kinetics and was expressed as a half-life value (to.5) which is the time for half of the initial external deposit to penetrate.…”

Section: Penetration and Metabolismmentioning

confidence: 99%

Characterization of the Organophosphoms-resistant Mt Alford, Gracemere and Silkwood Strains of the Cattle Tick, Boophilus microplus

Schnitzerling¹,

Schuntner²,

Roulston³

et al. 1974

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Dosage-mortality tests on larval ticks have indicated that the Mt Alford and Gracemere strains of B. micro pius differ from the Biarra and Ridgelands strains respectively, not only as previously reported by exhibiting markedly greater resistance to both chlorpyrifos and diazinon, but also by exhibiting moderately greater resistance in the Mt Alford strain to bromophos-ethyl and dioxathion and in the Gracemere strain to carbophenothion and coumaphos. Their responses to other chemicals were similar to those of the Biarra and Ridgelands strains respectively.Tests of acetylcholinesterase (AChE) activity and kinetic studies of inhibition of AChE in Mt Alford and Gracemere larvae indicated the presence of enzymes with relatively insensitive components similar to those of Biarra and Ridgelands AChE respectively.The penetration of [I4C]chlorpyrifos was similar in Mt Alford, Gracemere, Biarra and Ridgelands larvae, but of the chlorpyrifos metabolized considerably less was recovered as the oxygen analogue in Mt Alford and Gracemere larvae. This difference appeared to be due to greater hydrolytic activity. It was concluded that the greater resistance of these strains is due to enhanced detoxication.The previously described Mackay strain, although maintaining its pattern of resistance, was shown to have changed to one now exhibiting a reduced capacity for detoxication and a Ridgelands type of AChE. The Silkwood strain found nearly three years later was shown to be similar to the changed Mackay strain.

“…B Bromine oxidation of thio parent (Roulston et al 1966). C pH 11 bis-deethylation of parent (Stenersen 1969).…”

Section: Non-radioactive Reference Compoundsmentioning

confidence: 99%

“…Larvae were dosed with labelled or unlabelled chemicals by immersion in aqueous suspensions of chemical for 5 min (Roulston et al 1966). Duplicate samples weighing 0·2 g were used for metabolism studies and for the determination of AChE, while duplicate samples of c. 100 larvae were subsampled, after dosage, into paper packets and incubated for 24 h at 30°C and 90 % R.H. to determine mortality.…”

Section: Dosage Of Larvaementioning

confidence: 99%

Mechanisms of Resistance to Bromophos-ethyl in Two Strains of the Cattle Tick Boophilus microplus

Schuntner¹,

Thompson²

1978

Self Cite

B. micro plus larvae of the organophosphorus-resistant Biarra and Mt Alford strains were respectively 8 x and 35 x resistant to bromophos-ethyl compared with larvae of the standard organophosphorussusceptible Yeerongpilly strain. Both resistant strains had acetylcholinesterase with decreased sensitivity to inhibition by the oxon of bromophos-ethyl in vitro; this was the only resistance mechanism apparent in the Biarra strain but Mt Alford larvae were protected additionally by increased metabolism of the oxon in vivo to water-soluble products. Total degradation rates for the parent chemical were similar in all strains and relatively slow. Both bromophos-ethyl and its oxon were potent inhibitors of mixed-function oxidase in vivo and it seemed that the slow oxidative metabolism of bromophos-ethyl (the major pathway) could be attributed to substrate and/or product inhibition. No phenolic metabolites were detected and the major water-soluble metabolite was identified electrophoretically as 2,5-dichlorophenyl-o-ethyl phosphate. Some debrominated oxon was detected in all samples of larvae after dosage with bromophos-ethyl or with its oxon, indicating that oxidation of bromophos-ethyl to the oxon, debromination of the oxon followed by deethylation was a major degradative sequence.