Resistance to DDT in the catle trick, Boophilus microplus (Canestrini)

Abstract

Difficulty was experienced in controlling the cattle tick, on a herd at Rockhampton in central Queensland, by dipping in 0.5 per cent. w/v pp'-DDT. When an animal artificially infested with this strain was sprayed with 1 per cent. w/v pp'-DDT, only 26 per cent. of the engorged females falling from the animal over the 48-hr period after spraying failed to lay viable eggs, as compared with 64 per cent. of susceptible ticks falling from a similarly treated aninial. Both strains were, however, equally susceptible to "Diazinon". Laboratory concentration-response tests with a culture of the Rockhampton ticks indicated that the larvae exhibited a resistance 22 times that of a susceptible strain, and the engorged adult females a degree of resistance probably of the same order. The Rockhampton strain showed no significant resistance to dieldrin or toxaphene. There was no difference in susceptibility to DDT between adults of an 'early-falling' and a "late-falling" substrain of the resistant strain after selection for three generations.