The evolution of insecticide resistance is a model system for studying enzyme evolution. Three insect species have independently evolved catalytic organophosphate (OP) insecticide resistance through a single active-site mutation (Gly>Asp) in the αE7 enzyme. To explore the evolutionary potential of αE7, we subjected αE7 from the blowfly Lucilia cuprina to nine rounds of mutation and screening, resulting in a >1100-fold increase in the rate of OP-hydrolysis and a kcat/KM ~ 42000 s-1 M-1. Atomic resolution X-ray crystal structures of the evolutionary intermediates hint at the molecular basis for the increase in catalytic efficiency. Remarkably, mutations appearing in the later rounds yielded larger improvements in catalytic efficiency compared to initial mutations, indicating that the initial Gly>Asp mutation represents only a fraction of the αE7 evolutionary potential. Worryingly, this suggests that the Gly>Asp could be the first of many steps toward efficient OP-insecticide detoxification.