The kinetics and inhibition of p-nitrophenylacetate-hydrolysing esterases in a solitary bee, Megachile rotundata (Fab.).

1. The kinetics and inhibition of p-nitrophenylacetate hydrolysis by cytosolic esterases of female alfalfa leafcutting bees, Megachile rotundata (Fab.) was examined. 2. For p-nitrophenylacetate, the Km = 1.24 x 10(-4) M and Vmax = 2.29 x 10(-9) mol/s per mg protein. 3. Regarding four organophosphate insecticides, the mechanism of inhibition in all cases was mixed (competitive and uncompetitive) and, based on inhibition constants, the order of toxicity was naled greater than paraoxon greater than trichlorfon greater than oxydemeton methyl. 4. Comparisons are made to the honey bee, Apis mellifera.