Inheritance of Resistance to Organophosphorus Acaricides in the Cattle Tick, Boophilus Mioroplus

Abstract

An organophosphorus�resistant strain of the cattle tick B. microplus from central Queensland was crossed with a susceptible reference strain, the ticks being confined in plastic mating boxes glued to the skins of cattle. The resistance of Fl backcross and F2 larvae was compared with that of larvae of the parent strains by exposing larvae to filter-paper packets impregnated with solutions of dioxathion, carbophenothion, and formothion in olive oil. Some comparisons were also made by similarly exposing engorged adult females to these compounds or by injecting them into engorged females. The relative resistance of hybrids from reciprocal crosses, and the segregation ratios obtained in backcross F2 and repeated backcross progenies were generally in satisfactory agreement with expectations for a single incompletely dominant autosomal gene. Segregation into phenotypes was clearest with formothion for which the degree of resistance in homozygotes was up to 5200 times and in heterozygotes up to 950 times. Homozygotes were up to 12 and 6 times resistant to carbophenothion and dioxathion respectively.