Abstract: We report results of the base-line insecticide susceptibility of Aedes aegypti populations prior to an ongoing clinical trial quantifying the epidemiological impact of targeted indoor residual spraying (TIRS) in the city of Mérida, Yucatán, Mexico. Ae. aegypti eggs were collected using ovitraps from clusters of the TIRS project and randomly selected. The susceptibility of Ae. aegypti (F1) females to permethrin, deltamethrin, malathion and pirimiphos-methyl was quantified using dose and diagnostic times with the CDC bottle bioassay. Mortality at the diagnostic time and recovered individuals at 24 hours were recorded. Mosquito populations characterized as possibly developing resistance or resistant were exposed to enzyme inhibitors (PBO, DEF, EA) to determine which enzymatic mechanisms might be involved. Resistance was observed in most populations of Ae. aegypti exposed to permethrin (mortalities between 29% and 91%). For deltamethrin, one population showed 62% mortality, while in the rest ranged between 93% and 100%. For permethrin and deltamethrin, between 10% and 81% mosquitoes recovered 24 hours post-exposure. For pirimiphos-methyl, the populations showed no evidence of resistance (mortality above 93% at the diagnostic time and 100% at 24 hours post-exposure). Populations showed complete susceptibility to malathion. When using enzyme inhibitors, the contribution of resistance mediated by oxidases, esterases and gst was detected, which suggests that the populations identified as phenotypically resistant could be sharing enzymatic mechanisms.
.jpg "Alicia A. Méndez-Manzanero, Biologist (she/her/hers) photo")