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Esterase mediated insecticide resistance in the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae)
Abstract
Strains of German cockroach, Blattella germanica (L.) showed varying levels of resistance to chlorpyrifos, methyl parathion, propoxur, bendiocarb and cypermethrin. The esterase activity was higher in the resistant strains when compared with the susceptible strains. The specific activity of the enzymes increased with increases in substrate concentrations, pH and temperature. The K$\sb{\rm m}$ values for the resistant strains were nearly two fold higher than the susceptible strains. Non-denaturing gel electrophoresis revealed differences in isozyme composition. Ten esterase bands were detected in each strain. Esterase isozymes were isolated and analyzed for differences in activity. The isozymes E5, E6, E7 and E8 of resistant strains showed 2-5 fold increase in activity when compared with the susceptible strains. These isozymes constituted about 60% of the total activity in the resistant strains, compared with only about 40% in the susceptible strains. Subcellular distribution studies revealed that the majority of the esterase activity is present in the 100,000 g cytosolic fraction. Only a small portion of activity was membrane bound. The molecular weight of the esterase isozymes ranged between 48 and 81 kDa. The most active esterases (E5, E6, and E7) were purified from resistant and susceptible strains. About 68-138 fold purification with a 7.4-16.0% of total esterase recovery was achieved after various column chromatography and preparative gel electrophoresis. Elution profiles of resistant and susceptible strains were similar, but esterase E6 was quantitatively higher in the resistant strains. Kinetic analyses indicate no differences in K$\sb{\rm m}$ and V$\sb{\rm max}$ values between the resistant and susceptible strains. Inhibition of esterase activity by paraoxon, chlorpyrifos and propoxur did not suggest any structural differences in esterase E6 between strains. The results suggest that insecticide resistance in the German cockroach is partly due to the increased production of E6 esterase. The role of E6 may be sequestration of toxic molecules rather than hydrolysis.
Subject Area
Entomology
Recommended Citation
Prabhakaran, Suresh Kumar, "Esterase mediated insecticide resistance in the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae)" (1995). ETD collection for University of Nebraska-Lincoln. AAI9528829.
https://digitalcommons.unl.edu/dissertations/AAI9528829