Esterase activity in homogenates of three strains of the rust red flour beetle Tribolium castaneum (Herbst)

1. Esterase activity was measured in two malathion-resistant and one malathion-susceptible strain of the flour beetle Tribolium castaneum. 2. No A-esterase activity was found in homogenates of any strain. 3. The resistant Kano C strain showed only half of the esterase activity of the other two strains towards α-naphthylacetate, p-nitrophenylacetate and phenylacetate. The significance of this finding in relation to the resistance mechanism of the Kano C strain is discussed. 4. Some properties of the enzymes hydrolysing phenylacetate in insect homogenates and sheep serum are compared.