The outbreak of arbovirus vectors may result from a combination of human population growth, urbanization in tropical areas and a large expansion of the geographic distribution of Aedes aegypti. The objective of this research was to identify the populations of this vector in urban areas of four municipalities in the Baixada Cuiabana, using ovitraps, captured between October 2015 and November 2016. The electrophoresis technique was used, which aims to investigate the expression of esterase in biological samples in different environments. Esterases, such as carboxylesterase and cholinesterase, are involved in the development of resistance to chemical compounds in several insects, including the genus Aedes. The staining intensity of the gels was classified as "expressed bands", with weaker staining; and "overexpressed bands", with a darker color, indicative of the stronger presence of esterases. The analyses by the Mann-Whitney test of the Ae. aegypti population showed variability in esterase expression patterns with time, seasons and sites, which may undergo selection pressures related to the rainfall regime. An important factor that represented a higher frequency of isoenzyme overexpression was the beginning of the rains, in November/2016. Variations in the expression of bands between individuals of a population and between populations within the same species in different periods and places were conclusive of the vector populations as polymorphic.

Esterases are groups of enzymes that increase the mechanism of action of insect vectors in their metabolic activity while under environmental pressure. The aim of this study was to analyze the level of �-esterase expression in Aedes aegypti populations in the municipalities of Cuiabá and Várzea Grande, MT as a way to contribute to vector research. Samples were collected through ovitraps in each municipality and allele results were analyzed by factorial ANOVA between months, locations and seasonal phase. The alleles of 385 Ae. aegypti individuals demonstrated the highest expressions during the ebb period, significantly between months (F7,377=6.89; p<0.01) and between sites (F1,383=11.01). Expressed and superexpressed alleles decreased in Mar/2016, during the "peak water" period and resumed from May/2016 to Nov/2016. Regarding the frequency, expressed alleles increased in Várzea Grande, during the flood period with the highest precipitation. There was an increasing tendency of the expressed alleles with precipitation and the frequency values between Oct/2015 (30%±88) and Feb/2016 (89±55%); meanwhile, for the superexpressed alleles, this occurred during the ebb period (42±91%). Várzea Grande specimens reached a higher frequency of expressed alleles (75±41.36%), but there was a reduction of overexpressed alleles in both municipalities (F2,13=12.39; p<0.01). The results obtained in this study indicate that the esterase isoenzyme method was sensitive enough to detect variations in allele frequency in natural Ae. aegypti populations, which implies an increased metabolic activity over the period examined.