INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Characterization of General Esterases from Methyl Parathion-Resistant and -Susceptible Populations of Western Corn Rootworm (Coleoptera: Chrysomelidae)

A consistent correlation between elevated esterase activity and methyl parathion resistance among Nebraska western corn rootworm, Diabrotica virgifera virgifera LeConte, populations has previously been documented. Characterization of general esterase activity using naphtholic esters as model substrates indicated that differences between resistant and susceptible strains could be maximized by optimizing assay conditions. The optimal conditions identiÞed here were similar to those reported for other insect species. The majority of general esterase activity was found in the cytosolic fractions of resistant populations, whereas the activity wasmore evenly distributed between cytosolic andmitochondrial/nuclear fractions in the susceptible population. General esterase activity was predominately located in the adult thorax and abdomen. Although there were signiÞcant differences in general esterase activities between resistant and susceptible populations, the differences exhibited in single beetle activity assays did not provide sufÞcient discrimination to identify resistant individuals. In contrast, single larva activity assays provided greater discrimination and could be considered as an alternative to traditional bioassay techniques.