Resistance to certain organophosphorus ixodicides in the bont tick, Amblyomma hebraeum Koch, in the Republic of South Africa and Swaziland.

A series of in vitro trails confirmed resistance in the three-host tick, Amblyomma hebraeum Koch, to the organophosphorus ixodicides, dioxathion, chlorfenvinphos, quintiofos, bromophos-ethyl and a dioxathion/chlorfenvinphos combination. The results of a routine survey showed that a resistance factor of greater than 100x was present in the offspring of ticks in six of 115 field isolates tested. These six isolates were confined to the lowveld areas of the province of Natal, Republic of South Africa, and Swaziland. Ticks in a further 59 isolates were less susceptible than the reference strain. Resistance was present in all three tick instars. This is the first recorded resistance to the organophosphorus group of ixodicides by multi-host ticks in Africa.