Aedes aegypti es el principal vector del dengue alrededor del mundo. El control químico de larvas y adultos se basa principalmente en insecticidas organofosforados y piretroides; para los cuales se ha registrado el desarrollo de resistencia en campo. El manejo de la resistencia requiere evaluar la rapidez con la que ésta se desarrolla y la posible generación de resistencia cruzada entre ambos grupos de insecticidas. Este estudio evaluó durante siete generaciones el efecto de la selección con lambda-cialotrina sobre Ae. aegypti en el desarrollo de la resistencia a este piretroide y sus consecuencias en la aparición de resistencia cruzada a los insecticidas temefós, malatión y permetrina en condiciones de laboratorio. Se obtuvieron adultos a partir de larvas colectadas en campo en Cúcuta (Colombia) y sus descendientes fueron expuestos a concentraciones del insecticida incrementadas gradualmente cada generación. El desarrollo de la resistencia fue confirmado usando bioensayos en larvas y adultos. La selección incrementó los grados de resistencia (GR) en cada generación (1,25X promedio). La población de la generación F7 fue altamente resistente a lambda-cialotrina en adultos (F1 = 100% mortalidad disminuyó a F7 = 35% de mortalidad) y larvas (GR 50 F1 = 24,22X hasta GR50 F7 = 61,52X) al compararla con la cepa de referencia en susceptibilidad Rockefeller. La cepa resistente a lambda-cialotrina no presentó resistencia cruzada con temefós y malatión (organofosforados), pero sí a permetrina (piretroide). La información obtenida sugiere que la rotación de piretroides con organofosforados continúa siendo una alternativa apropiada para manejar la aparición de la resistencia en las estrategias de control del dengue.

Aedes aegypti is the main vector of dengue virus worldwide. The chemical control of larvae and adults is based principally on organophosphate and pyrethroid insecticides, for which resistance has developed in the field. The management of resistance requires evaluating how rapidly it can develop and the possible generation of cross-resistance between both groups of insecticides. This study evaluates the effects of selection on Ae. aegypti with lambda-cyhalo-thrin on the development of resistance to this pyrethroid over seven generations and its impact on the appearance of cross-resistance to temephos, malathion, and permethrin insecticides under laboratory conditions. Adults were obtained from larvae collected in the field in Cúcuta (Colombia) and the descendants were exposed to gradually increasing concentrations of insecticides each generation. The development of resistance was confirmed using bioassays on the larvae and adults. Selection increased the ratio of resistance (RR) in each generation (1.25X average). At generation F7, the population was highly resistant to lambda-cyhalothrin for both adults (100% mortality in F1 decreased to 35% mortality in F7) and larvae (RR50 F1 = 24.22 X, RR50 F7 = 61.52 X) when compared to the susceptibility of Rockefeller, the reference line. The line resistant to lambda-cyhalothrin did not present cross-resistance to temephos and malathion (organophosphates), but did present resistance to permethrin (pyrethroid). The information obtained suggests that the rotation of organophosphates and pyrethroids continues to be an appropriate alternative for managing the appearance of resistance on dengue control strategies.

El control de los mosquitos vectores de malaria se realiza principalmente con aplicaciones de insecticidas ya sea en las paredes internas de las viviendas o en toldillos. Por lo anterior, la vigilancia de la resistencia a insecticidas en estas especies es fundamental para la definición de planes y estrategias de control de malaria. El propósito de este estudio fue determinar las dosis diagnósticas de varios insecticidas de uso en salud pública para los principales vectores de malaria en Colombia: Anopheles darlingi, A. albimanus y A. nuneztovari, utilizando la metodología de las botellas impregnadas desarrollada por los Centros para la Prevención y Control de Enfermedades. Se seleccionaron poblaciones naturales de las tres especies sometidas a baja o nula presión con insecticidas con las cuales se realizaron bioensayos para determinar las líneas base de susceptibilidad. Se establecieron las dosis diagnósticas (concentración del insecticida y tiempo diagnóstico) o curvas de saturación, para los insecticidas lambdacialotrina, deltametrina, fenitrotión, malatión y DDT para los tres vectores; ciflutrina, permetrina y propoxur para A. albimanus y A. darlingi; y etofenprox y bendiocarb para A. darlingi. Las dosis diagnósticas determinadas en estas poblaciones permitirán evaluar el estado de la resistencia a insecticidas de los principales vectores de malaria a lo largo de su distribución en Colombia, fortaleciendo el sistema de vigilancia de la resistencia y facilitando la toma de decisiones para un uso más adecuado de los insecticidas en el control de malaria en el país.

The control of mosquito vectors of malaria is largely based on insecticide applications, either on the inside walls of dwellings or on treated nets. For that reason, the surveillance of insecticide resistance in these species is essential for the definition of plans and strategies of malaria control. The purpose of this study was to determine the diagnostic doses of several insecticides used in public health for the main vectors of malaria in Colombia: Anopheles darlingi, A. albimanus and A. nuneztovari, using the methodology of impregnated bottles developed by the Centers for Disease Control and Prevention. Natural populations of the three species, submitted to low or no insecticide pressure, were selected with which bioassays were conducted to determine baseline susceptibility. Diagnostic doses (insecticide concentration and diagnostic time), or saturation curves, were established for the insecticides lambda-cyhalothrin, deltamethrin, fenitrothion, malathion and DDT for the three vectors; cyfluthrin, permethrin and propoxur for A. albimanus and A. darlingi, and etofenprox and bendiocarb for A. darlingi. The diagnostic doses determined in these susceptible populations will allow an evaluation of the status of insecticide resistance of the main malaria vectors across their distribution in Colombia, strengthening the resistance surveillance system and facilitating decision making for a more appropriate use of insecticides to control malaria in the country.

In order to establish the insecticide susceptibility status for Anopheles darlingi in Colombia, and as part of the National Network on Insecticide Resistance Surveillance, five populations of insects from three Colombian states were evaluated. Standardised WHO and CDC bottle bioassays, in addition to microplate biochemical assays, were conducted. Populations with mortality rates below 80% in the bioassays were considered resistant. All field populations were susceptible to deltamethrin, permethrin, malathion and fenitrothion. Resistance to lambda-cyhalothrin and DDT was detected in the Amé-Beté population using both bioassay methods with mortality rates of 65-75%. Enzyme levels related to insecticide resistance, including mixed function oxidases (MFO), non-specific esterases (NSE), glutathione S-transferases and modified acetylcholinesterase were evaluated in all populations and compared with a susceptible natural strain. Only mosquitoes from Amé-Beté presented significantly increased levels of both MFO and NSE, consistent with the low mortalities found in this population. The continued use of lambda-cyhalothrin for An. darlingi control in this locality has resulted in a natural resistance to this insecticide. In addition, DDT resistance is still present in this population, although this insecticide has not been used in Colombia since 1992. Increased metabolism through MFO and NSE may be involved in cross-resistance between lambda-cyhalothrin and DDT, although kdr-type nerve insensitivity cannot be discarded as a possible hypothesis. Additional research, including development of a kdr specific assay for An. darlingi should be conducted in future studies. Our data demonstrates the urgent need to develop local insecticide resistance management and surveillance programs throughout Colombia.