Inheritance of organochlorine resistance in the cattle tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) in East Africa

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Abstract
Single pair progenies (sibships) of three organochlorine resistant strains of Rhipicephalus appendiculatus Neum. from Kenya, Tanzania and Uganda showed similarity in dose-mortality response to γ-BHC. The homogeneous dose-mortality responses indicated such larvae have a similar high level of resistance, whereas the stepped nature of the dose-mortality curve for the heterogeneous sibships indicated that these sibships include both resistant and susceptible larvae. Crosses between the Uganda strain and the susceptible reference strain (Mwanza) indicated that a dominant gene exerts a major influence on resistance to γ-BHC and dieldrin. For some heterogeneous sibships the dose-mortality response indicated a significant departure from a 1:1 ratio of susceptible: resistant larvae. The deviation could be reduced by increasing the susceptible background genotype. The deviation differed in direction for different crosses, suggesting a genetic influence. The deviations occurred in all three resistant strains. Line selection of deviating sibships in either direction was unsuccessful.