PARTIAL CHARACTERIZATION OF PHOSPHOTRIESTERASES FROM ORGANOPHOSPHATE-SUSCEPTIBLE AND ORGANOPHOSPHATE-RESISTANT POPULATIONS OF RHYZOPERTHA-DOMINICA (COLEOPTERA, BOSTRICHIDAE)

Phosphotriesterases from lesser grain borer, Rhyzopertha dominica (Col eoptera: Bostrichidae), were partially characterized and their roles i n conferring organophosphate resistance were assessed. The optimal tem perature for determination of phosphotriesterase activity was 37 degre es C using paraoxon as a substrate. The pH profile suggests the presen ce of more than one phosphotriesterase with different pH optima. The k inetic parameters. K-m and V-max, determined at 37 degrees C were 5.19 x 10(-3) M and 80.22 nmol/hr/mg protein, respectively, for the suscep tible population and 5.82 x 10(-3) M and 189.47 nmol/hr/mg protein, re spectively, for the resistant population. Frequency of individuals wit h high phosphotriesterase activity within the resistant population was significantly higher than that of the susceptible population. Phospho triesterase activity in each of 15 resistant populations was also sign ificantly higher than that of the susceptible population. Significantl y higher hydrolysing efficiency to paraoxon, as judged by the V-max va lue and higher phosphotriesterase activity in resistant populations, s uggests the involvement of phosphotriesterases as an organophosphate r esistance mechanism in lesser grain borer. (C) 1997 Academic Press.