D.D.T. and its related compounds seem to be the only group of the new
contact insecticides against which the blue tick has not been able to build up
any resistance. Toxaphene as well as Parathion are definitely less effective against
the B.H.C.-resistant strain and higher concentrations are needed to achieve a good
control. Dieldrin and related compounds, which otherwise are very powerful
insecticides appear to be of little value for the control of the B.H.C.-resistant
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