Biochemical Genetics of Resistance to Organophosphorus Acaricides in Three Strains of the Cattle Tick, Boophilus microplus

Abstract

Three aspects of the biochemical genetics of resistance to organophosphorus compounds in the Biarra (B), Mackay (M) and Ridgelands (R) strains of the cattle tick B. microp/us were studied. These were: decreased acetylcholinesterase (AChE) activity in adult brains of strains Band M; decreased AChE sensitivity to inhibitors in adult brains and in larvae of strains B, M and R; and increased detoxication in larvae and adult females of strain M. Comparisons were made with a susceptible reference strain (S). Microspectrophotometric estimations of AChE activity in histochemical preparations of whole brains showed that hybrids had levels of activity approximately intermediate between those of the parental strains. Homogenates of brains from hybrids assayed biochemically gave similar but more precise results which indicated that decreased brain AChE activity was neither recessive nor dominant (degree of dominance, D = + O· 02) in strain B and incompletely recessive (D = - O· 26) in strain M. The proportions of brains showing decreased AChE activity in testcross and F 2 progenies indicated that decreased AChE activity in strains Band M is controlled by single autosomal genes.