Esterase Activity in Strains of Aedes Aegypti (Diptera: Culicidae) Tolerant and Susceptible to the Organophosphate Insecticide Malathion

The correlation between esterase-6 band intensities and malathion LT50 in 3-day-old adults of the mosquito Aedes aegypti was significantly high. Three strains of mosquito were used: a field-tolerant and highly laboratory-selected strain, Villa Palmeras (VP); a population of Villa Palmeras that had not been laboratory selected for resistance and had regressed, Unselected Villa Palmeras (UVP); and a susceptible strain never exposed to malathion, Triple Marker (TM). Following horizontal electrophoresis on polyacrylamide gels, the intensity of esterase bands was measured by scanning densitometry. Band intensities in VP were significantly greater than in TM, but those in VP and UVP were not significantly different. The reciprocal F1's of the crosses between VP and TM showed intermediate resistance and an intermediate esterase intensity significantly different from either parental strain. Available evidence indicates that esterase-6 is one resistance mechanism among others. The measurement of esterase-6 intensity as a guide to field tolerance of Ae. aegypti to malathion is considered briefly.