Synthetic pyrethroid resistance in field samples in the cattle tick (Boophilus microplus).

First evidence of resistance to synthetic pyrethroids in the cattle tick in Australia, other than the pre-existing cross-resistance in DDT-resistant ticks, has emerged. Three new strains have been investigated and characterised. The first, detected in central Queensland, showed increased ability to detoxify pyrethroids resulting in a marginal loss of efficacy of all pyrethroid tickicides tested, except flumethrin. Subsequently two more strains have been detected, with serious implications for chemical tick control. The first, from southern Queensland, has a high level of specific resistance to flumethrin. The second, from central Queensland, has a broad spectrum resistance encompassing all pyrethroids currently in use. The toxicology and biochemistry of these new resistant strains have been investigated and alternative tickicides evaluated. The significance of these latest developments is discussed.