The rapid spread of the single host arsenic-resistant blue tick, B. decoloratus, a transmitter of piroplasmosis and anaplasmosis, seriously affected a large and important cattle ranching area in South Africa.

Biological tests, using the laboratory technique described in an earlier paper, enabled the most effective “Gammexane” preparations to be rapidly selected from numbers of experimental dips. The technique was also employed as a supplement to chemical analyses of dip wash samples where only the total hexachlorocyclohexane and not gamma isomer was estimated. Twenty-thousand adult female ticks were used in these in vitro tests. Oil emulsions seemed more active than dispersible powders or pastes, but all tests indicated that 50 parts per million “Gammexane” should satisfactorily control the tick in the field.

Laboratory tests with larvae of the blue tick showed that “Gammexane” had a persistent action and was very toxic to this stage of the tick. Excellent control oflarval ticks could be anticipated in the field.

In vitro tests indicated that “Gammexane” was effective against the two- and three-host ticks, R. evertsi, R. appendiculatus, A. hebraeum, H. silacea and Hyalomma spp., but hand dressing and shorter dipping intervals might be necessary to control these ticks in the field. The sheep paralysis tick, I. pilosus, seemed to be resistant to “Gammexane” but was readily killed by arsenic.