Acaricide resistance in single and multi-host ticks and strategies for control.

The majority of reports, concerning resistance in multi-host ticks, continue to be confined to the cyclodiene group and lindane, with sparse references to resistance affecting the organophosphorus acaricides. In contrast, the resistance picture in Boophilus spp., particularly in relation to B. microplus in Australia, continues to degenerate. Recent reports, documenting the emergence of a complex of pyrethroid resistant strains in the latter species, are the cause of considerable current concern, due to the lack of a suitable, commercially available, replacement group. These developments reinforce the need for a close examination of the strategies recommended for the management of acaricide resistance, particularly for Boophilus spp. The choice of options to select, in circumstances following the detection of resistance to an acaricide, is limited to those aimed at preserving the use of the affected chemical, or selection of an effective alternative, either from within the same class, or from a new acaricide group. Success of the former options, including tactics such as increased concentration or eradication of resistant alleles, and the rational choice of alternative acaricides for use in localized areas where necessary, are critically dependent on early detection of a newly emerged resistance mechanism, its localization, and an understanding of its spectrum of effect. Avermectins and acarine growth regulators show promise as potential future tick control agents. However, the dearth of new chemistry in this area stresses the importance of developing optimal strategies to extend the effective life of these and currently available compounds, in areas where they remain effective.(ABSTRACT TRUNCATED AT 250 WORDS)