Toxaphene-resistant cattle ticks (Boophilus microplus (Canestrini)) occurring in Queensland

Abstract

Cattle ticks on four herds in southern Queensland survived dipping in a vat charged with 0.5 per cent. w/v toxaphene, which nevertheless disinfested a fifth herd. Protective periods afforded by toxaphene against attachment of resistant larvae were much shorter than against susceptible strains. Laboratory concentration-response tests on a culture of the toxaphene-resistant ticks indicated that the median lethal concentration of toxaphene for engorged females was 19 times higher than that of a reference strain, and t h at f o r the larvae was also significantly higher. The toxaphene-resistant ticks were not affected when cows were sprayed with 0.05 per cent. w/v gamma-BHC. This was consistent with an earlier history of BHC resistance in the ticks on these herds. Spraying trials indicated no marked arsenic resistance in the toxaphene-resistant ticks. The mortality of the toxaphene-resistant ticks on cattle sprayed with 0.5 per cent. W/V pp'-DDT, and the protective period against larval reinfestation, were as high as usually observed in other tick populations. A very high kill resulted from spraying the toxaphene-resistant ticks with 0.05 per cent. w/v diazinon. Subcutaneous injections of peanut oil solutions of lindane, dieldrin, and aldrin at the rate of 25 mg toxicant/kg host body weight were without effect on toxaphene-resistant ticks.