Linkage and Dominance Characteristics of Genes for Resistance to Organophosphorus Acaricides and Allelic Inheritance of Decreased Brain Cholinesterase Activity in Three Strains of the Cattle Tick, Boophilus microplus

Abstract

Resistance to the organophosphorus acaricides diazinon, dimethoate and formothion in the Biarra (B), Mackay (M) and Ridgelands (R) strains respectively of the cattle tick B. microplus has been shown previously to be controlled in each strain by a single incompletely dominant autosomal genetic factor. A very similar mode of inheritance of fenthion resistance in strain B has now been demonstrated with no departure in degree of dominance of resistance from the mean value of + 0·57 common to these strains exposed to these chemicals. No F 1 larval progeny from the following crossings were appreciably more resistant than their parents to these chemicals: R x B-bromophos ethyl and fenthion; B x M-carbaryl, chlorfenvinphos, chlorpyrifos, diazinon, dimethoate, ethion, fenthion and formothion; M x R-chlorfenvinphos, diazinon, dimethoate, ethion, formothion. The field importance of this absence of overdominance is discussed.