Esterase variation in Tribolium confusum (Coleoptera: Tenebrionidae): genetic analysis of interstrain crosses in relation to malathion resistance

General esterase activity variation among individuals and strains of Tribolium confusum (du Val) is mostly due to a single electrophoretic locus. A strain (CFxlH) selected for very strongly staining isozyme (EST2), was reciprocally crossed with the black mutant laboratory strain (CFbb) which has very weak EST2. EST2 is not linked to the black locus and is inherited as a monogenic, autosomal trait. Similar results were obtained when CFxlH was reciprocally crossed with the sister strain (CFxlL) selected for low activity. Slight deviations from Mendelian expectation in the latter crosses suggest that maternally inherited effects modify EST2 activity in these strains.CFbb and CFxlL both have low EST2 activity, and when intercrossed, all offspring had the EST2L pattern, suggesting that the EST2 loci in the two strains are the same or very tightly linked.Malathion resistance in one strain (MN61) seems to be inherited in a monofactorial fashion, with dominance of the resistant allele. MN61 is fixed for the high-activity EST2 phenotype. Addition of triphenyl phosphate (TPP) synergised the effects of the pesticide, indicating that malathion resistance is due to carboxylesterase activity. CFxlH and CFxlL had similar malathion resistance despite the dramatic difference in EST2 activity: resistance is not due to EST2, the major contributor to the hydrolysis of α-naphthyl acetate (and probably other naphthyl esters).