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.

Previous studies have reported genetic differences between wild-caught sylvatic, domestic and laboratory pop-ulations of several Triatominae species. The differences between sylvatic and laboratory colonies parallel are similar to the differences observed between sylvatic and domestic populations. Laboratory colonies are frequently used as references for field populations, but the consequences of founder events on the genetic makeup of laboratory or domestic populations are rarely quantified. Our goal was to quantify the genetic change in Rhodnius pallescens populations artificially submitted to founder effects via laboratory colonization. We compared the genetic makeup of two sylvatic populations and their laboratory descendants using a panel of 10 microsatellite markers. Both sylvatic populations were initially collected from palm trees, but the colonies differed in the number of founder insects and amount of time kept in the laboratory. We evaluated allelic polymorphism, differences between expected and observed heterozygosity, estimates of population differentiation (Fst) and inbreeding (Fis, Fit) and cluster analyses based on Nei's distances. We found a unique genetic structure for each sample population, with significant differentiation between the field insects and each of the laboratory generations. These analyses showed strong founder effects and showed that genetic drift had led to a genetic equilibrium over several generations of isolation. Our results suggest that laboratory colonies of R. pallescens have a different genetic structure than their wild relatives and similar processes likely affect other Triatominae laboratory stocks.

Rhodnius pallescens is the main vector of Trypanosoma cruzi in Panama and one of the most relevant secondary vectors in Colombia. Despite the importance of this species, there is limited knowledge about the genetic variability along its geographical distribution. In order to evaluate the degree of karyotype variability we analyzed the meiotic behavior and banding pattern of the chromosomes of 112 males of R. pallescens coming from different regions of Colombia and Panama. Using the C-banding technique we identified two chromosomal patterns or cytotypes characterized by differences in the amount, size and distribution of constitutive heterochromatic regions in the chromosome complement (2n = 20 autosomes plus XY in males). The individuals can be easily classified in each cytotype by the analysis of the chromosomes during first meiotic prophase. The frequencies of the cytotypes are variable according to the geographic origin of the populations. This chromosomal divergence together with morphological data supports the existence of three genetically different populations of R. pallescens and provides new information to understand the distribution dynamics of this species.