Ixodicidal resistance in Boophilus microplus (Canestrini) in the Republic of South Africa and Transkei.

A series of in vitro trials using unfed larvae and fully fed adult ticks confirmed ixodicidal resistance in the one-host Pantropical Blue Tick, Boophilus microplus (Canestrini). Fifty-seven of 64 field isolates were resistant to arsenic; 10 of 56 were resistant to toxaphene; 1 of 5 were resistant to lindane; 3 of 5 were resistant to dieldrin; 3 of 19 were resistant to DDT and 8 of 55 were resistant to the organophosphorus ixodicide, dioxathion. One of the field isolates resistant to dioxathion was also highly resistant to the carbamate, carbaryl, and to the organophosphorus ixodicides benoxophos and diazinon. A second was resistant to the organophosphorus ixodicides benoxophos, diazinon, carbophenothion, dicrotophos, ethion, fenitrothion and quintiofos. Low levels of resistance, less than 3X, were shown to chlorfenvinphos and coumaphos. No resistance was shown to chlorpyrifos, bromophos ethyl or the diamidine ixodicide, amitraz. In hand-spraying trials no variation in the susceptibility of an organophosphorus resistant strain or the susceptible laboratory strain to amitraz was observed. This is the first recorded resistance to ixodicides by B. microplus in Africa.