Resistance to toxaphene by the Bont tick, Amblyomma hebraeum (Koch)

A series of in vitro and in vivo trials confirmed resistance by the three-host Bont tick, Amblyomma hebraeum (Koch), to Toxaphene in the Cape, Natal and Transvaal Provinces of the Republic of South Africa, and in Swaziland and Transkei. Resistance was present in 80 of 97 field strains examined. Lindane and DDT resistance was present in the one field strain tested. The results of comparative in vivo hand spraying and plunge dipping trials confirmed those of the larval in vitro tests, thus validating the usefulness of this latter technique for identifying changes of susceptibility in field tick strains to ixodicides. Selection of Toxaphene resistance in A. hebraeum occurred within a period of four years when a 14-day interval of treatment was used continuously. The presence of all three tick instars in all stages of engorgement at the time of each treatment under this regimen is thought to have enhanced this selection.