The major cause of resistance mechanism in mosquitoes is the detoxification and degradation of
insecticides by overproduction of various metabolic enzymes. Quantitative metabolic enzyme assays
of carboxylesterases (α and β), mixed function oxidases (MFO), and glutathione S-transferases (GST)
have been commonly used in the detection of insecticide resistance due to its sensitive nature even at low
frequencies. For the present study, larval strains of Culex quinquefasciatus Say and Aedes aegypti (L) were
collected from the Cochin Corporation, Kerala, India, and were assayed to organophosphate temephos
and carbamate propoxur. The resistance ratio of median lethal time for temephos and propoxur from the
field population of C. quinquefasciatus and A. aegypti is higher than the laboratory population. Elevated
levels of α and β esterase enzyme were observed with the ratio of 1.6 and 1.54 for C. quinquefasciatus
and 1.51 and 1.47 for A. aegypti. In Culex mosquitoes, 1.71, and in Aedes, 1.64 fold increase in GST
enzyme level and 1.38 and 1.3 fold increase for the MFO level determined. The study results revealed
the urgent needs of improving the vector control methods by introducing alternative techniques and
strategies against mosquitoes.