The existence of an organophosphorus-resistant strain of Boophilus microplus (Canestrini) in Queensland (M strain) was recorded in 1964. Although resistant to several commercial insecticides, this strain, known as the Ridgelands resistant tick, remained susceptible to others, notably ethion and coumaphos. At the end of 1965 another strain resistant to these and other insecticides was discovered at Biarra, near Brisbane (L strain). This strain is known as the Biarra resistant tick. The activities of numerous insecticides against larvae of the L strain and a susceptible strain have been compared. The results indicate that the L strain is highly resistant to most of the organophosphorus or carbamate compounds tested against it. None so far tested is normally effective against it. Among those to which it is highly resistant are carbaryl, carbophenothion, Compound 4072 (2-chloro-1-(2,4-dichlorophenyl) vinyl diethyl phosphate), coumaphos, diazinon, dioxathion, and ethion. Several compounds of possible value against the Biarra strain also are revealed by these tests. The abnormal susceptibility to 2,4,5, tri-halogenated phenyl phosphorothioates of larvae of the M strain is recorded.
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Shaw et al. (1968) studied this question.