Molecular diversity of genes related to biological rhythms (period and timeless) and insecticide resistance (Na V and ace-1) in Anopheles darlingi.

BACKGROUND: Malaria is a public health concern in the Amazonian Region, where Anopheles darlingi is the main vector of Plasmodium spp. Several studies hypothesised the existence of cryptic species in An. darlingi, considering variations in behaviour, morphological and genetic aspects. Determining their overall genetic background for vector competence, insecticide resistance, and other elements is essential to better guide strategies for malaria control. OBJECTIVES: This study aimed to evaluate the molecular diversity in genes related to behaviour and insecticide resistance, estimating genetic differentiation in An. darlingi populations from Amazonian localities in Brazil and Pacific Colombian region. METHODS: We amplified, cloned and sequenced fragments of genes related to behaviour: timeless (tim) and period (per), and to insecticide resistance: voltage-gated sodium channel (Na V ) and acetylcholinesterase (ace-1) from 516 An. darlingi DNA samples from Manaus, Unini River, Jaú River and Porto Velho - Brazil, and Chocó - Colombia. We discriminated single nucleotide polymorphisms (SNPs), determined haplotypes and evaluate the phylogenetic relationship among the populations. FINDINGS: The genes per, tim and ace-1 were more polymorphic than Na V . The classical kdr and ace-1 R mutations were not observed. Phylogenetic analyses suggested a significant differentiation between An. darlingi populations from Brazil and Colombia, except for the Na V gene. There was a geographic differentiation within Brazilian populations considering per and ace-1. CONCLUSIONS: Our results add genetic data to the discussion about polymorphisms at population levels in An. darlingi. The search for insecticide resistance-related mechanisms should be extended to more populations, especially from localities with a vector control failure scenario.

Molecular diversity of genes related to biological rhythms (period and timeless) and insecticide resistance (Na V and ace-1) in Anopheles darlingi

BACKGROUND Malaria is a public health concern in the Amazonian Region, where Anopheles darlingi is the main vector of Plasmodium spp. Several studies hypothesised the existence of cryptic species in An. darlingi, considering variations in behaviour, morphological and genetic aspects. Determining their overall genetic background for vector competence, insecticide resistance, and other elements is essential to better guide strategies for malaria control. OBJECTIVES This study aimed to evaluate the molecular diversity in genes related to behaviour and insecticide resistance, estimating genetic differentiation in An. darlingi populations from Amazonian localities in Brazil and Pacific Colombian region. METHODS We amplified, cloned and sequenced fragments of genes related to behaviour: timeless (tim) and period (per), and to insecticide resistance: voltage-gated sodium channel (Na V ) and acetylcholinesterase (ace-1) from 516 An. darlingi DNA samples from Manaus, Unini River, Jaú River and Porto Velho - Brazil, and Chocó - Colombia. We discriminated single nucleotide polymorphisms (SNPs), determined haplotypes and evaluate the phylogenetic relationship among the populations. FINDINGS The genes per, tim and ace-1 were more polymorphic than Na V . The classical kdr and ace-1 R mutations were not observed. Phylogenetic analyses suggested a significant differentiation between An. darlingi populations from Brazil and Colombia, except for the Na V gene. There was a geographic differentiation within Brazilian populations considering per and ace-1. CONCLUSIONS Our results add genetic data to the discussion about polymorphisms at population levels in An. darlingi. The search for insecticide resistance-related mechanisms should be extended to more populations, especially from localities with a vector control failure scenario.

Deltamethrin resistance in Chagas disease vectors colonizing oil palm plantations: implications for vector control strategies in a public health-agriculture interface.

BACKGROUND: Triatomine bugs are responsible for the vectorial transmission of the parasite Trypanosoma cruzi, etiological agent of Chagas disease, a zoonosis affecting 10 million people and with 25 million at risk of infection. Several triatomine species of the genus Rhodnius have been found inhabiting palm crowns where insects can find shelter in leaves axils and blood from palm-associated vertebrates. Rhodnius prolixus insects have been collected in oil palms in Colombia, and high T. cruzi infection rates were found. Since pest control is carried out in oil palm plantations, continuous exposure to insecticides could be occurring in these triatomines. Some insecticides suggested for pest control in oil palm plantations are also recommended for triatomine control in human dwellings. In this study, our objective was to assess if triatomines inhabiting oil palms exhibit resistance to deltamethrin, an insecticide used for vector control. METHODS: Rhodnius prolixus nymphs were sampled in oil palms located in Tauramena, Colombia. To determine deltamethrin resistance, biological and biochemical assays were carried out on fifth-instar nymphs from the F1 generation. For biological assays, pure and commercial deltamethrin were used, and in biochemical assays, activities of detoxifying enzymes related to pyrethroid resistance, such as oxidases, esterases and transferases, were quantified. RESULTS: Deltamethrin lethal dosage 50 and 90 in R. prolixus from oil palms was significantly higher than in those from a susceptible colony suggesting possible deltamethrin resistance. Moreover, mortality with commercial deltamethrin was very low in insects from oil palms. In biochemical assays, the activity of evaluated detoxifying enzymes was significantly higher in R. prolixus from oil palms than in those from the susceptible colony. CONCLUSIONS: Possible deltamethrin resistance found in R. prolixus insects from oil palms could threaten traditional vector control strategies in urban settings if insecticide-resistant triatomines can migrate from oil palms plantations. In palm oil producer countries such as Colombia, the oil palm plantations are growing constantly during the last years. We suggest that pest control strategies in oil palm crops should include triatomine surveillance and toxicological monitoring, especially in zones with several Chagas disease cases.

Enhanced vector surveillance to control arbovirus epidemics in Colombia.

In the wake of the Zika epidemic, there has been intensified interest in the surveillance and control of the arbovirus vectors Aedes aegypti and Aedes albopictus, yet many existing surveillance systems could benefit from improvements. Vector control programs are often directed by national governments, but are carried out at the local level, resulting in the discounting of spatial heterogeneities in ecology and epidemiology. Furthermore, entomological and epidemiological data are often collected by separate governmental entities, which can slow vector control responses to outbreaks. Colombia has adopted several approaches to address these issues. First, a web-based, georeferenced Aedes surveillance system called SIVIEN AEDES was developed to allow field entomologists to record vector abundance and insecticide resistance data. Second, autocidal gravid oviposition (AGO) traps are deployed as an alternative way to measure vector abundance. Third, data collected by SIVIEN AEDES are used to develop mathematical models predicting Ae. aegypti abundance down to a city block, thus allowing public health authorities to target interventions to specific neighborhoods within cities. Finally, insecticide resistance is monitored through bioassays and molecular testing in 15 high-priority cities, providing a comprehensive basis to inform decisions about insecticide use in different regions. The next step will be to synchronize SIVIEN AEDES data together with epidemiological and climatic data to improve the understanding of the drivers of local variations in arbovirus transmission dynamics. By integrating these surveillance data, health authorities will be better equipped to develop tailored and timely solutions to control and prevent Aedes-borne arbovirus outbreaks.

Tras la epidemia del Zika, se ha intensificado el interés en vigilar y controlar los vectores de arbovirus Aedes aegypti y Aedes albopictus. Aun así, muchos de los sistemas existentes de vigilancia necesitan mejorar. En general son los gobiernos nacionales los que dirigen los programas de control de vectores, aunque estos programas se llevan a cabo a nivel local, por lo que no se tiene en cuenta la heterogeneidad del lugar en cuanto a las características ecológicas y epidemiológicas. Además, normalmente los datos entomológicos y epidemiológicos son recopilados por entidades gubernamentales distintas, lo que puede ralentizar el control de vectores durante un brote. Colombia ha puesto en marcha varias iniciativas para abordar estas cuestiones. La primera es un sistema en línea de geolocación del mosquito Aedes, llamado SIVIEN AEDES, para que los entomólogos de campo puedan registrar la abundancia de los mosquitos vectores y recoger datos sobre la resistencia a los insecticidas. La segunda es la implantación de ovitrampas autocidales para hembras grávidas (AGO, por su sigla en inglés), que son una manera alternativa de medir la abundancia de vectores. La tercera iniciativa es utilizar los datos recogidos por el sistema SIVIEN AEDES para elaborar modelos matemáticos que predigan la abundancia del A. aegypti hasta incluso en una cuadra de ciudad, de manera que las autoridades de salud pública puedan dirigir las intervenciones a vecindarios específicos dentro de las ciudades. Por último, Colombia está vigilando en quince ciudades prioritarias la resistencia a los insecticidas mediante ensayos biológicos y análisis moleculares, de esta forma se genera una base de datos exhaustiva sobre la que fundamentar las decisiones acerca del uso de insecticidas en las diferentes regiones. El paso siguiente será sincronizar los datos recopilados por el sistema SIVIEN AEDES con datos epidemiológicos y climáticos para poder entender mejor cómo se originan las variaciones locales en la dinámica de transmisión de los arbovirus. Al integrar estos datos de vigilancia, las autoridades sanitarias estarán mejor equipadas para encontrar soluciones oportunas y adecuadas para la situación específica, a fin de controlar y prevenir los brotes de arbovirus transmitidos por el Aedes.

Depois da epidemia de zika, intensificou-se o interesse na vigilância e controle dos vetores arbovirais Aedes aegypti e Aedes albopictus, mas muitos dos sistemas de vigilância existentes poderiam ser aprimorados. Muitos programas de controle de vetores são dirigidos pelos governos nacionais, mas implementados no âmbito local, o que leva à desconsideração de heterogeneidades espaciais em aspectos ecológicos e epidemiológicos. Além disso, é comum que dados entomológicos e epidemiológicos sejam coletados por agências governamentais separadas, o que pode desacelerar o controle de vetores em resposta aos surtos. A Colômbia adotou vários enfoques para abordar esses problemas. Primeiro, um sistema de vigilância de Aedes georreferenciado e baseado na Internet, chamado SIVIEN AEDES, foi desenvolvido para permitir aos entomólogos de campo registrar a abundância de vetores e a resistência aos inseticidas. Segundo, ovitrampas letais para fêmeas grávidas estão sendo mobilizadas como maneira alternativa de medir a abundância vetorial. Terceiro, os dados coletados pelo SIVIEN AEDES estão sendo utilizados para desenvolver modelos matemáticos para prever a abundância do Ae. aegypti até o nível de quadra/quarteirão, permitindo assim às autoridades de saúde pública direcionar intervenções para bairros específicos em cada município. Finalmente, a resistência aos inseticidas é monitorada através de ensaios biológicos e testes moleculares em 15 cidades de alta prioridade, o que proporciona uma base abrangente para subsidiar decisões sobre o uso de inseticida em diferentes regiões. O próximo passo será sincronizar os dados do SIVIEN AEDES com dados epidemiológicos e climáticos para melhorar a compreensão dos fatores que impulsionam variações locais na dinâmica da transmissão arboviral. Ao integrar esses dados de vigilância, as autoridades de saúde estarão mais bem equipadas para desenvolver soluções personalizadas e oportunas para controlar e prevenir os surtos de arbovírus transmitidos por mosquitos do gênero Aedes.

Enhanced vector surveillance to control arbovirus epidemics in Colombia

[ABSTRACT]. In the wake of the Zika epidemic, there has been intensified interest in the surveillance and control of the arbovirus vectors Aedes aegypti and Aedes albopictus, yet many existing surveillance systems could benefit from improvements. Vector control programs are often directed by national governments, but are carried out at the local level, resulting in the discounting of spatial heterogeneities in ecology and epidemiology. Furthermore, entomological and epidemiological data are often collected by separate governmental entities, which can slow vector control responses to outbreaks. Colombia has adopted several approaches to address these issues. First, a web-based, georeferenced Aedes surveillance system called SIVIEN AEDES was developed to allow field entomologists to record vector abundance and insecticide resistance data. Second, autocidal gravid oviposition (AGO) traps are deployed as an alternative way to measure vector abundance. Third, data collected by SIVIEN AEDES are used to develop mathematical models predicting Ae. aegypti abundance down to a city block, thus allowing public health authorities to target interventions to specific neighborhoods within cities. Finally, insecticide resistance is monitored through bioassays and molecular testing in 15 high-priority cities, providing a comprehensive basis to inform decisions about insecticide use in different regions. The next step will be to synchronize SIVIEN AEDES data together with epidemiological and climatic data to improve the understanding of the drivers of local variations in arbovirus transmission dynamics. By integrating these surveillance data, health authorities will be better equipped to develop tailored and timely solutions to control and prevent Aedes-borne arbovirus outbreaks.

[RESUMEN]. Tras la epidemia del Zika, se ha intensificado el interés en vigilar y controlar los vectores de arbovirus Aedes aegypti y Aedes albopictus. Aun así, muchos de los sistemas existentes de vigilancia necesitan mejorar. En general son los gobiernos nacionales los que dirigen los programas de control de vectores, aunque estos programas se llevan a cabo a nivel local, por lo que no se tiene en cuenta la heterogeneidad del lugar en cuanto a las características ecológicas y epidemiológicas. Además, normalmente los datos entomológicos y epidemiológicos son recopilados por entidades gubernamentales distintas, lo que puede ralentizar el control de vectores durante un brote. Colombia ha puesto en marcha varias iniciativas para abordar estas cuestiones. La primera es un sistema en línea de geolocación del mosquito Aedes, llamado SIVIEN AEDES, para que los entomólogos de campo puedan registrar la abundancia de los mosquitos vectores y recoger datos sobre la resistencia a los insecticidas. La segunda es la implantación de ovitrampas autocidales para hembras grávidas (AGO, por su sigla en inglés), que son una manera alternativa de medir la abundancia de vectores. La tercera iniciativa es utilizar los datos recogidos por el sistema SIVIEN AEDES para elaborar modelos matemáticos que predigan la abundancia del A. aegypti hasta incluso en una cuadra de ciudad, de manera que las autoridades de salud pública puedan dirigir las intervenciones a vecindarios específicos dentro de las ciudades. Por último, Colombia está vigilando en quince ciudades prioritarias la resistencia a los insecticidas mediante ensayos biológicos y análisis moleculares, de esta forma se genera una base de datos exhaustiva sobre la que fundamentar las decisiones acerca del uso de insecticidas en las diferentes regiones. El paso siguiente será sincronizar los datos recopilados por el sistema SIVIEN AEDES con datos epidemiológicos y climáticos para poder entender mejor cómo se originan las variaciones locales en la dinámica de transmisión de los arbovirus. Al integrar estos datos de vigilancia, las autoridades sanitarias estarán mejor equipadas para encontrar soluciones oportunas y adecuadas para la situación específica, a fin de controlar y prevenir los brotes de arbovirus transmitidos por el Aedes.

[RESUMO]. Depois da epidemia de zika, intensificou-se o interesse na vigilância e controle dos vetores arbovirais Aedes aegypti e Aedes albopictus, mas muitos dos sistemas de vigilância existentes poderiam ser aprimorados. Muitos programas de controle de vetores são dirigidos pelos governos nacionais, mas implementados no âmbito local, o que leva à desconsideração de heterogeneidades espaciais em aspectos ecológicos e epidemiológicos. Além disso, é comum que dados entomológicos e epidemiológicos sejam coletados por agências governamentais separadas, o que pode desacelerar o controle de vetores em resposta aos surtos. A Colômbia adotou vários enfoques para abordar esses problemas. Primeiro, um sistema de vigilância de Aedes georreferenciado e baseado na Internet, chamado SIVIEN AEDES, foi desenvolvido para permitir aos entomólogos de campo registrar a abundância de vetores e a resistência aos inseticidas. Segundo, ovitrampas letais para fêmeas grávidas estão sendo mobilizadas como maneira alternativa de medir a abundância vetorial. Terceiro, os dados coletados pelo SIVIEN AEDES estão sendo utilizados para desenvolver modelos matemáticos para prever a abundância do Ae. aegypti até o nível de quadra/quarteirão, permitindo assim às autoridades de saúde pública direcionar intervenções para bairros específicos em cada município. Finalmente, a resistência aos inseticidas é monitorada através de ensaios biológicos e testes moleculares em 15 cidades de alta prioridade, o que proporciona uma base abrangente para subsidiar decisões sobre o uso de inseticida em diferentes regiões. O próximo passo será sincronizar os dados do SIVIEN AEDES com dados epidemiológicos e climáticos para melhorar a compreensão dos fatores que impulsionam variações locais na dinâmica da transmissão arboviral. Ao integrar esses dados de vigilância, as autoridades de saúde estarão mais bem equipadas para desenvolver soluções personalizadas e oportunas para controlar e prevenir os surtos de arbovírus transmitidos por mosquitos do gênero Aedes.

Estado de la sensibilidad a los insecticidas de uso en salud pública en poblaciones naturales de Aedes aegypti (Diptera: Culicidae) del departamento de Casanare, Colombia / Status of insecticide susceptibility of public health use in natural populations of Aedes aegypti (Diptera: Culicidae) of Casanare, Colombia

Introducción. La resistencia fisiológica de Aedes aegypti constituye una de las principales amenazas para la eficacia de los programas de control de la transmisión del dengue. Objetivos. Determinar el estado de la sensibilidad a los insecticidas en poblaciones naturales de A. aegypti de tres localidades endémicas para dengue en Casanare. Materiales y métodos. Se obtuvieron mosquitos adultos de A. aegypti a partir de estados inmaduros recolectados en siete poblaciones naturales correspondientes a tres municipios. La primera generación filial fue empleada para evaluar los mecanismos bioquímicos asociados con alteración de ß -esterasas inespecíficas y enzimas monooxigenasas del grupo citocromo P450. La segunda generación permitió evaluar la sensibilidad a los insecticidas a partir de bioensayos, usando la metodología propuesta por los Centers for Disease Control and Prevention para mosquitos adultos y la técnica para larvas de la Organización Mundial de la Salud. Resultados. Todas las poblaciones evaluadas registraron resistencia al organoclorado DDT y a los piretroides lambdacialotrina y permetrina. Dos presentaron sensibilidad a la deltametrina y cinco a la ciflutrina. Se registró sensibilidad a los organofosforados temefos, malatión y fenitrotión. Ninguna población incrementó las ß -esterasas, pero sí incrementaron las enzimas P450 en dos poblaciones de Yopal. Conclusiones. Los resultados sugieren que las enzimas P450 pueden jugar un papel importante en la resistencia a los piretroides y al DDT; aun así, otros mecanismos de resistencia pueden estar actuando en las poblaciones. La sensibilidad a los insecticidas organofosforados permitiría continuar con el uso de este grupo químico para interrumpir la transmisión del dengue en Casanare.

Introduction: Physiological resistance of Aedes aegypti is a major threat to effective control programs in the transmission of dengue virus. Objective: To determine the status of susceptibility to insecticides used in public health, in natural populations of A. aegypti from three endemic dengue localities of Casanare. Materials and methods: Adult mosquitoes were recovered from A. aegypti immature stages from seven natural populations collected for three municipalities. The first filial generation was used to assess the biochemical mechanisms associated with loss of susceptibility: nonspecific esterase (NSE) and enzyme cytochrome P450 monooxygenases group. The second filial generation allowed us to evaluate the susceptibility to insecticides from bioassays using the CDC 1998 methodology for adult mosquitoes and WHO 1981 technique for larvae. Results: In the seven adult populations recorded loss of susceptibility to organochlorine DDT and pyrethroids lambda-cyhalothrin and permethrin. Two populations showed susceptibility to deltamethrin and five populations showed susceptibility to cyfluthrin. There was a susceptibility to organophosphates temephos, malathion and fenitrothion in all populations. No population showed increased NSE but an increase of P450 in two populations Conclusions: It appears that the P450 may play an important role in resistance to pyrethroids and DDT, still other resistance mechanisms may be acting in populations. Susceptibility to organophosphate allows continued use of this chemical group to interrupt transmission of dengue in Casanare.

[Status of insecticide susceptibility of public health use in natural populations of Aedes aegypti (Diptera: Culicidae) of Casanare, Colombia]. / Estado de la sensibilidad a los insecticidas de uso en salud pública en poblaciones naturales de Aedes aegypti (Diptera: Culicidae) del departamento de Casanare, Colombia.

INTRODUCTION: Physiological resistance of Aedes aegypti is a major threat to effective control programs in the transmission of dengue virus. OBJECTIVE: To determine the status of susceptibility to insecticides used in public health, in natural populations of A. aegypti from three endemic dengue localities of Casanare. MATERIALS AND METHODS: Adult mosquitoes were recovered from A. aegypti immature stages from seven natural populations collected for three municipalities. The first filial generation was used to assess the biochemical mechanisms associated with loss of susceptibility: nonspecific esterase (NSE) and enzyme cytochrome P450 monooxygenases group. The second filial generation allowed us to evaluate the susceptibility to insecticides from bioassays using the CDC 1998 methodology for adult mosquitoes and WHO 1981 technique for larvae. RESULTS: IN the seven adult populations recorded loss of susceptibility to organochlorine DDT and pyrethroids lambda-cyhalothrin and permethrin. Two populations showed susceptibility to deltamethrin and five populations showed susceptibility to cyfluthrin. There was a susceptibility to organophosphates temephos, malathion and fenitrothion in all populations. No population showed increased NSE but an increase of P450 in two populations CONCLUSIONS: It appears that the P450 may play an important role in resistance to pyrethroids and DDT, still other resistance mechanisms may be acting in populations. Susceptibility to organophosphate allows continued use of this chemical group to interrupt transmission of dengue in Casanare.

[Susceptibility to insecticides of Anopheles darlingi Root 1840, in two locations of the departments of Santander and Caquetá, Colombia]. / Sensibilidad de Anopheles darlingi Root 1840 a insecticidas, en dos localidades de los departamentos de Santander y Caquetá, Colombia.

INTRODUCTION: Physiological resistance to insecticides used in public health is the main factor to define strategies for malaria vector control. OBJECTIVE: To determine the physiological status of insecticide susceptibility of natural populations of An. darlingi from two localities in the Santander and Caquetá departments. MATERIALS AND METHODS: Wild adult Anopheles darlingi females were collected and bioassays using technical grade insecticides were performed following the methods recommended both by the World Health Organization (WHO, 1981) and the Centers for Diseases Control and Prevention (CDC, 1998). RESULTS: The natural populations of An. darlingi from the villages of Gerumano, Solano, Caqueta and Las Margaritas, San Vicente de Chucurí, Santander, showed susceptibility to the pyrethroids lambdacyhalothrin and deltamethrin, to the organochlorate DDT and to the organophosphate fenitrothion with 100% mortality rates in all of the CDC tests and between 95 and 100% in the tests performed following the WHO methods. For the carbamate propoxur the 88% mortality rate obtained in the village of Gerumano following the methods recommended by WHO coincides with the surveillance methods established for surveillance of this molecule. CONCLUSIONS: Chemical products whose active ingredients are the molecules tested are effective for control of An. darlingi in the study sites.

Estado de la susceptibilidad de poblaciones naturales / Susceptibility of natural populations of dengue vector to insecticides in Colombia

Introducción. La resistencia fisiológica de las poblaciones naturales de Aedes aegypti a los insecticidas de uso en salud pública, disminuye la eficacia del control químico utilizado para interrumpir la transmisión de dengue durante los brotes y epidemias. Objetivo. Determinar el estado de la susceptibilidad al carbamato propoxur, a los organofosforados adulticidas malatión y fenitrotión y al larvicida temefos, de 13 poblaciones naturales de Ae. aegypti en ocho municipios: una de Bucaramanga y dos de Sabana de Torres en el departamento de Santander; dos de Girardot y dos de La Mesa en Cundinamarca; dos de Villavicencio y dos de Puerto López en el Meta; una de San José del Guaviare, en Guaviare, y una de Florencia en Caquetá. Materiales y métodos. Las pruebas de susceptibilidad consistieron en bioensayos estandarizados de la Organización Mundial de la Salud (OMS), 1981, y botellas de los Centers for Disease Control and Prevention (CDC), 1998. Se aplicaron pruebas colorimétricas para determinar los niveles de enzimas como posibles responsables de la reducción de la susceptibilidad a insecticidas organofosforados y al carbamato propoxur. Resultados. Todas las poblaciones presentaron susceptibilidad a malatión y propoxur. Para el temefos, solo cuatro de las trece localidades evaluadas registraron susceptibilidad. Con respecto a los posibles mecanismos de desintoxicación enzimática, en siete de las once poblaciones naturales se registraron valores superiores al punto de corte para esterasas inespecíficas, solamente en Bucaramanga se presentó un incremento en las enzimas monooxigenasas del citocromo P450, pero en ninguna población se registró acetilcolinestarasa modificada. Conclusiones. La susceptibilidad generalizada a los organofosforados adulticidas evaluados, indica que el malatión, el insecticida más utilizado en Colombia para interrumpir la transmisión del dengue, sigue siendo eficaz. Las particularidades de los resultados de la resistencia fisiológica a insecticidas de las comunas de un mismo municipio, evidenciaron un fenómeno localizado de manera específica en espacio y tiempo.

Introduction. Physiological resistance of natural population of Aedes aegypti to insecticides contribute to the decreased efficacy of chemical control as a main control strategy during dengue outbreaks. Objective. The susceptibility status of Ae. aegypti was assessed for the carbamate propoxur, the adulticide malathion and the larvicide temephos on 13 natural populations of Ae. aegypti immature forms were taken from 8 Colombian localities. These included the following: Bucaramanga (1), Sabana de Torres (2), Girardot (2), La Mesa (2), Villavicencio (2), Puerto López (2), San José del Guaviare (1) and Florencia (1). Materials and methods. Susceptibility tests mainly consisted of the standardized bioassay outlined by WHO (1981) and CDC bottles (1998). Colorimetric tests were undertaken to determine enzyme levels possibly responsible for the reduction of susceptibility to organophosphate and carbamate insecticides. Results. All specimens demonstrated susceptibility to malathion and propoxur insecticides. Four of the 13 populations revealed susceptibility to the temephos larvicide. Seven of 11 populations showed a limited increase in values for nonspecific esterase enzymes. The Bucaramanga population was the only one which showed an increase in the cytochrome P450 monooxygenases enzymes. Neither population was found with modified acetilcolinesterase. Conclusions. The widespread susceptibility to organophosphates used as adulticides indicated that malathion, the most used insecticide in Colombia, remains effective in interrupting the transmission of dengue. Physiological resistance to insecticides occurring in communities of a single township proved to be a localized phenomenon.

Sensibilidad de Anopheles darlingi Root 1840 a insecticidas, en dos localidades de los departamentos de Santander y Caquetá, Colombia / Susceptibility to insecticides of Anopheles darlingi Root 1840, in two locations of the departments of Santander and Caquetá, Colombia

Introducción. La sensibilidad fisiológica a los insecticidas usados en salud pública es el principal factor que se debe tener en cuenta en la selección de las estrategias de control en los vectores de malaria. Objetivo. Determinar el estado de sensibilidad fisiológica de Anopheles darlingi a insecticidas, en dos localidades de los departamentos de Santander y Caquetá. Materiales y métodos. Se recolectaron hembras silvestres de An. darlingi y se hicieron bioensayos según la metodología de la Organización Mundial de la Salud (OMS, 1981) y de los Centers for Disease Control and Prevention (CDC, 1998), usando moléculas insecticidas grado técnico. Resultados Las poblaciones naturales de An. darlingi de las veredas Gerumano en Solano (Caquetá) y la vereda Las Margaritas en San Vicente de Chucurí (Santander) mostraron sensibilidad a los insecticidas piretroides lambdacialotrina y deltametrina, al organoclorado DDT y al organosofosforado fenitrotión, con mortalidades del 100 % en todas la pruebas del CDC y entre 95 y 100 % para las de la OMS. Para el carbamato propoxur, la mortalidad de 88 % en la población de Gerumano, evaluada por las pruebas de la OMS, coincide con valores de vigilancia para esta molécula. Conclusión. Los productos químicos que tienen como ingrediente activo las moléculas evaluadas, son eficaces para el control de An. darlingi en los sitios de estudio.

Introduction. Physiological resistance to insecticides used in public health is the main factor to define strategies for malaria vector control. Objective. To determine the physiological status of insecticide susceptibility of natural populations of An. darlingi from two localities in the Santander and Caquetá departments. Materials and methods. Wild adult Anopheles darlingi females were collected and bioassays using technical grade insecticides were performed following the methods recommended both by the World Health Organization (WHO, 1981) and the Centers for Diseases Control and Prevention (CDC, 1998). Results. The natural populations of An. darlingi from the villages of Gerumano, Solano, Caqueta and Las Margaritas, San Vicente de Chucurí, Santander, showed susceptibility to the pyrethroids lambdacyhalothrin and deltamethrin, to the organochlorate DDT and to the organophosphate fenitrothion with 100% mortality rates in all of the CDC tests and between 95 and 100% in the tests performed following the WHO methods. For the carbamate propoxur the 88% mortality rate obtained in the village of Gerumano following the methods recommended by WHO coincides with the surveillance methods established for surveillance of this molecule. Conclusions. Chemical products whose active ingredients are the molecules tested are effective for control of An. darlingi in the study sites.

[Susceptibility of natural populations of dengue vector to insecticides in Colombia]. / Estado de la susceptibilidad de poblaciones naturales.

INTRODUCTION: Physiological resistance of natural population of Aedes aegypti to insecticides contribute to the decreased efficacy of chemical control as a main control strategy during dengue outbreaks. OBJECTIVE: The susceptibility status of Ae. aegypti was assessed for the carbamate propoxur, the adulticide malathion and the larvicide temephos on 13 natural populations of Ae. aegypti immature forms were taken from 8 Colombian localities. These included the following: Bucaramanga (1), Sabana de Torres (2), Girardot (2), La Mesa (2), Villavicencio (2), Puerto López (2), San José del Guaviare (1) and Florencia (1). MATERIALS AND METHODS: Susceptibility tests mainly consisted of the standardized bioassay outlined by WHO (1981) and CDC bottles (1998). Colorimetric tests were undertaken to determine enzyme levels possibly responsible for the reduction of susceptibility to organophosphate and carbamate insecticides. RESULTS: All specimens demonstrated susceptibility to malathion and propoxur insecticides. Four of the 13 populations revealed susceptibility to the temephos larvicide. Seven of 11 populations showed a limited increase in values for nonspecific esterase enzymes. The Bucaramanga population was the only one which showed an increase in the cytochrome P450 monooxygenases enzymes. Neither population was found with modified acetilcolinesterase. CONCLUSIONS: The widespread susceptibility to organophosphates used as adulticides indicated that malathion, the most used insecticide in Colombia, remains effective in interrupting the transmission of dengue. Physiological resistance to insecticides occurring in communities of a single township proved to be a localized phenomenon.