The inheritance of dieldrin-resistance in the cattle tick, Boophilus microplus

Abstract

Adults of a dieldrin-resistant straiu of cattle tick from southern Queensland were crossed with adults of a susceptible reference strain, by means of cardboard mating boxes glued to the skins of cattle. The F1 and backcross larvae were tested for resistance by enclosure in filter paper packets impregnated with oil solutions of dieldrin. The corresponding engorged adult females were tested by injection with oil solutions of dieldrin. There was no evidence of significant departure from a 1 : 1 ratio of resistant and susceptible phenotypes in the backcrosses, and there was little difference between the composition of the F1 reciprocal crosses or between the backcrosses derived from them. Dieldrin-resistance in this strain appears to be due to a single, dominant autosomal gene. Dieldrin-resistant ticks in a multiresistant strain from central Queensland steadily declined from 50–60% to an undetectable percentage in a laboratory population bred in the absence of dieldrin for 24 generations.