Respuesta a atrayentes químicos y actividad horaria de Anopheles Meigen spp. (Diptera: Culicidae) en un área malárica del estado Bolívar, Venezuela / Response to chemical attractants and host seeking behavior of Anopheles Meigen spp. (Diptera: Culicidae) in a malaria endemic area of Bolívar State, Venezuela

Se evaluó la eficiencia de la trampa Mosquito Magnet Liberty PlusTM (MMLP) cebada con los atrayentes químicos 1-octen-3-ol (octenol) y Lurex 3TM (L-ácido láctico) junto con dióxido de carbono (CO2) para recolectar anofelinos en la localidad Ye'kwana de Boca de Nichare, municipio Sucre, estado Bolívar, Venezuela. La trampa fue operada entre las 18:00 y 06:00 horas, durante 10 noches por mes, durante cuatro meses (Julio ­ Octubre, 2015), alternándose cada noche el atrayente. A fin de caracterizar la actividad nocturna de los anofelinos, cada cuatro horas se cambiaba la jaulita donde eran atrapados los mosquitos. Se capturaron cinco especies de Anopheles y cuatro de Culicinae, siendo las más abundantes, Anopheles (Nyssorhynchus) darlingi Root y Anopheles (Nyssorhynchus) oswaldoi (Peryassú) sensu lato. El ANOVA factorial no paramétrico de Transformación de Rangos Alineados para la variable atrayente y sus interacciones con especie e intervalo horario no fueron estadísticamente significativas (p > 0.05). Estas especies muestran comportamientos diferentes: An. darlingi tiene el pico de actividad nocturna entre las 22:00 y 02:00 horas, mientras que en An. oswaldoi s.l. se observa un incremento de la actividad nocturna progresivamente que se mantiene durante el intervalo 02:00-06:00 horas. Los resultados permiten concluir que la trampa MMLP cebada con octenol o Lurex es un método alternativo de recolección de mosquitos para la vigilancia entomológica en áreas maláricas remotas con población indígena. La actividad horaria de los vectores An. darlingi y An. oswaldoi s.l. sugiere que el uso de mosquiteros tratados con insecticidas puede resultar un método efectivo para el control de la transmisión de malaria en esta zona del país(AU)

The efficiency of the Mosquito Magnet Liberty PlusTM (MMLP) trap was evaluated baited with the chemical attractants 1-octen-3-ol (octenol) and Lurex3M (L-lactic acid) together with carbon dioxide (CO2) to collect anophelines in the Amerindian village Boca de Nichare, Sucre municipality, Bolívar State, Venezuela. The trap was operated between 18:00 and 06: hours, 10 nights per month for four months (July-October 2015), the attractants were alternated nightly. To determine the host seeking behavior of anophelines, the trap cage was changed every 4 hours. Five species of Anopheles and four of Culicinae were collected; Anopheles (Nyssorhynchus) darlingi Root and Anopheles oswaldoi (Peryassú) sensu lato were the most abundant species collected. The Align Rank Transform (ART) test for nonparametric ANOVA for the variable attractant and its interactions with species and hour interval were not significant (p > 0.05). An. darlingi and An. oswaldoi s.l. showed contrasting host seeking activity: An. darlingi showed a peak between 22:00 and 02:00 hours, while in An. oswaldoi s.l. there was a steady increase in activity up to the interval 02:00-06:00 hours. The MMLP trap baited either with octenol or Lurex is an alternative method for entomological surveillance in remote Amerindian malaria endemic areas. The biting activity of the vectors An. darlingi and An. oswaldoi s.l. suggests that the use of long-lasting insecticide treated nets could be an effective method to control the transmission of malaria in this area(AU)

Successes and failures of sixty years of vector control in French Guiana: what is the next step?

Since the 1940s, French Guiana has implemented vector control to contain or eliminate malaria, yellow fever, and, recently, dengue, chikungunya, and Zika. Over time, strategies have evolved depending on the location, efficacy of the methods, development of insecticide resistance, and advances in vector control techniques. This review summarises the history of vector control in French Guiana by reporting the records found in the private archives of the Institute Pasteur in French Guiana and those accessible in libraries worldwide. This publication highlights successes and failures in vector control and identifies the constraints and expectations for vector control in this French overseas territory in the Americas.

Anopheles darlingi polytene chromosomes: revised maps including newly described inversions and evidence for population structure in Manaus

Salivary gland polytene chromosomes of 4th instar Anopheles darlingi Root were examined from multiple locations in the Brazilian Amazon. Minor modifications were made to existing polytene photomaps. These included changes to the breakpoint positions of several previously described paracentric inversions and descriptions of four new paracentric inversions, two on the right arm of chromosome 3 and two on the left arm of chromosome 3 that were found in multiple locations. A total of 18 inversions on the X (n = 1) chromosome, chromosome 2 (n = 7) and 3 (n = 11) were scored for 83 individuals from Manaus, Macapá and Porto Velho municipalities. The frequency of 2Ra inversion karyotypes in Manaus shows significant deficiency of heterozygotes (p < 0.0009). No significant linkage disequilibrium was found between inversions on chromosome 2 and 3. We hypothesize that at least two sympatric subpopulations exist within the An. darlingi population at Manaus based on inversion frequencies.

Caracterización de hábitats larvales de anofelinos en el municipio Sifontes del estado Bolívar, Venezuela / Characterization of anophelines larval habitats in the municipality of Sifontes, Bolívar State, Venezuela

El municipio Sifontes, ubicado en el noreste del estado Bolívar, constituye el principal foco de malaria de Venezuela. Durante el quinquenio 2010-2014, se registró en el municipio un aumento considerable de la morbilidad con una fuerte tendencia al incremento, cerrando 2014 con la cifra record de 51.603 casos, 58% de la malaria del país en el año. Con el objeto de estudiar la distribución espacial de las larvas de anofelinos en los hábitats acuáticos y su relación con las variables ambientales, se hicieron colectas mensuales de larvas en hábitats representativos de los diferentes tipos existentes en la zona, entre septiembre 2002 y diciembre 2003. El Análisis de Correspondencia Canónica (CANOCO) indica que a nivel de hábitat (humedal), la presencia de las especies de Anopheles está determinada por el tipo y la dinámica hídrica del hábitat, mientras que a nivel de microhábitat (cucharonazo) las especies se ubican a lo largo de un gradiente dominado por el tipo de vegetación, y en menor grado por la luz solar y el color aparente del agua. Esto permitió establecer grupos de especies a priori, tales como las del subgénero Nyssorhynchus, asociadas a la luz solar y a ciertas plantas acuáticas, o las de los subgéneros Anopheles y Stethomyia, An. (Lophopodomyia) squamifemur y Chagasia bonneae asociadas a ambientes sombreados y carentes de vegetación. Los resultados ayudan a comprender mejor la relación de las especies de anofelinos con el medio ambiente y resaltan la importancia de variables como la dinámica hídrica, luz solar, vegetación y color aparente del agua para determinar su ocurrencia en el hábitat acuático.

The Municipality of Sifontes, located in the northeast of Bolivar State, is the main malaria foci in Venezuela. A considerable increase in malaria morbidity was recorded in the Municipality during the decade 2010-2014, with a record figure of 51.603 cases for 2014, 58% of the malaria for the country. In order to study the spatial distribution of anopheline inmature stages in the larval habitats and its relation to environmental variables, monthly collections were carried out in larval habitats representatives of the different types present in the area between September 2002 and December 2003. The Canonic Correspondance Analysis (CANOCO) showed that at the larval habitat level the Anopheles species is determined by the type and dynamics of the habitat, while at the microhabitat level (dip) the species are located along a gradient dominated by the type of vegetation, and in a lesser degree by the exposure to sun light and apparent water color. These allowed to established group of species a priori, such as those of the subgenus Nyssorhynchus associated to sun light and certain aquatic plants, or the subgenus Anopheles and Sthetomyia, An. squamifemur and Chagasia bonneae associated to shaded environments and lack of vegetation. The results help to understand the relationship of anopheline species with the environment and the importance of variables such s water dynamics, sun light, vegetation and water apparent color to determine its occurrence in the larval habitat.

Effect of Bacillus sphaericus Neide on Anopheles (Diptera: Culicidae) and associated insect fauna in fish ponds in the Amazon

ABSTRACTWe analyzed the effects of Bacillus sphaericus on Anopheles larvae and on the associated insect fauna in fish farming ponds. Five breeding sites in the peri-urban area of the city of Manaus, AM, Brazil, were studied. Seven samples were collected from each breeding site and B. sphaericus was applied and reapplied after 15 days. The samples were made at 24 h before application, 24 h post-application and 5 and 15 days post-application. We determined abundance, larval reduction and larval density for Anopheles, and abundance, richness, Shannon diversity index and classified according to the functional trophic groups for associated insect fauna. A total of 904 Anopheles larvae were collected and distributed into five species. Density data and larval reduction demonstrated the rapid effect of the biolarvicide 24 h after application. A total of 4874 associated aquatic insects belonging to six orders and 23 families were collected. Regression analysis of diversity and richness indicated that the application of the biolarvicide had no influence on these indices and thus no effect on the associated insect fauna for a period of 30 days. B. sphaericus was found to be highly effective against the larvae of Anopheles, eliminating the larvae in the first days after application, with no effect on the associated insect fauna present in the fish ponds analyzed.

Fluctuación poblacional y hábitat larval de anofelinos en el municipio Sifontes, estado Bolívar, Venezuela / Population fluctuation and larval habitat of anopheline in the Municipality of Sifontes, Bolivar State, Venezuela

El Municipio Sifontes, ubicado en el noreste del estado Bolívar, Venezuela, constituye uno de los principales focos de malaria del país debido a causas naturales y antrópicas.Durante el decenio 2004-2013, se registró en este municipio un aumento considerable del número de casos, cerrando 2013 con 42.981 casos, 56% de la malaria del país. Con el objeto de describir la dinámica poblacional de las principales especies de anofelinos, en fase pre-adulta, entre septiembre 2002 y diciembre 2003, se hicieron colectas mensuales en cuerpos de agua representativos de los diferentes tipos existentes en el municipio. Anopheles triannulatus Neiva & Pinto sensu lato fue la especie más abundante y ubicua en toda el área de estudio, seguida de An. albitarsis Lynch Arribalzaga s.l., mientras que An. darlingi Root fue encontrada principalmente en lagunas y ríos. La variabilidad estacional en la abundancia larval estuvo condicionada principalmente por la especie de anofelino y el tipo de hábitat que ésta coloniza, de tal forma que el efecto de la lluvia sobre la abundancia de las especies depende de la dinámica hídrica del hábitat larval, si bien en general, la abundancia de larvas tiende a ser mayor durante el periodo de transición lluvia-sequía y sequía. Los resultados de este estudio contribuyen a dilucidar la relación de la dinámica poblacional de los anofelinos con el patrón de lluvias en la región estudiada.

Sifontes Municipality in the north-east of Bolivar State is one of the main malaria foci in Venezuela due to both natural and anthropic factors. Between 2004 and 2013 a significant increase in the number of cases were reported for this region: at the close of 2013, 42.981 cases had been registered representing 56% of the total number of cases reported in the country. Between September 2002 and December 2003 anopheline larvae were collected monthly to study population fluctuations in different habitats representative of the study area. Anopheles triannulatus Neiva & Pinto sensu lato was the most abundant species collected followed by An. albitarsis Lynch Arribalzaga s.l., while An. darlingi Root was mainly found in lagoons and rivers. Seasonal variations in larval abundance were mainly determined by anopheline species and the type of larval habitat exploited by each one. Anopheline species are thus differentially influenced by rainfall according to the water dynamics of their larval habitats, but in general abundance is higher during the transitions between rainfall-drought and the dry season. These results help us to understand the relationships between anopheline population dynamics and rainfall patterns in this region. In addition, they contribute to our basic knowledge of the bio-ecology of anopheline vectors important for the epidemiology, surveillance and control of malaria in Sifontes Municipality.

Evaluación preliminar de la eficiencia de Bacillus sphaericus en un área endémica a malaria del estado Bolívar, Venezuela / Preliminary evaluation of the effectiveness of Bacillus sphaericus in an malaria-endemic region in Bolívar state, Venezuela

El municipio Sifontes del estado Bolívar es la principal área endémica a malaria de Venezuela. Durante los cinco años anteriores al estudio se reportaron allí un promedio anual de 14 mil casos, alcanzándose en 2009 la cifra de 19.408, constituyendo una situación de epidemia. En la búsqueda de estrategias alternativas al uso de insecticidas, se evaluó la eficiencia para el control de malaria de una formulación comercial de Bacillus sphaericus Neide (VectoLex® CG 7,5%). Entre mayo 2010 y mayo de 2011 se aplicó biolarvicida con motomochila (Solo®) a dosis de 20-30 kg/ha a frecuencia mensual en todos los criaderos de Anopheles darlingi, An. marajoara y An. nuneztovari ubicados alrededor de las viviendas de cuatro comunidades de la parroquia San Isidro de este municipio, acompañadas de colectas de anofelinos adultos con atrayente humano y trampa de luz CDC y ultravioleta. Después de 48 semanas de aplicación, la reducción de 80% de la malaria en el área, más la reducción de la densidad de larvas en los criaderos, muestran que el biolarvicida es eficiente para controlar malaria. Los resultados también sugieren que la prevalencia de larvas es un buen indicador en un programa de control de vectores basado en la aplicación de biolarvicida, no así la de adultos, cuya abundancia no se corresponde con la de larvas. Es la primera vez que se evalúa la eficiencia de B. sphaericus para controlar malaria en Venezuela, considerándose estos resultados prometedores, si el tratamiento de criaderos con biolarvicida es selectivo y se hace a la cobertura, frecuencia y dosis correctas, e integrado a otras estrategias de control de vectores.

The Sifontes municipality in Bolivar state is the principal malaria-endemic region in Venezuela. During the five years prior to the study an annual average of 14,000 cases was reported reaching an epidemic level of 19,408 cases in 2009. As part of the search for vector control measures that could be used as alternatives to insecticides, a commercial formulation of Bacillus sphaericus Neide (VectoLex® CG 7.5%) was evaluated. Between May 2010 and May 2011 monthly dosages of 20-30 kg/ha of Vectolex were sprayed using a motorized backpack (Solo®) in larval Anopheles darlingi, An. marajoara and An. nuneztovari habitats close to houses in four communities in the parish of San Isidro, Sifontes municipality. In parallel, adult anophelines were captured using human baits, CDC light traps and ultraviolet light traps. After 48 weeks of application there was an 80% reduction in malaria as well as a decrease in larval density demonstrating the effectiveness of B. sphaericus for the control of this disease. Moreover, the results suggest that larval prevalence is good indicator for biolarvicide based malaria control programs whereas the abundance of adults, which does not correlate with larval abundance, is not. This is the first time that the effectiveness of B. sphaericus for malaria control has been evaluated in Venezuela. These results show that spraying larval habitats for malaria control can be effective when integrated with other vector control strategies if the treatment is selective and carried out at the correct frequency and dosage in order to ensure adequate coverage of the larval habitat.

Composition, abundance and aspects of temporal variation in the distribution of Anopheles species in an area of Eastern Amazonia

Introduction The diverse and complex environmental conditions of the Amazon Basin favor the breeding and development of Anopheles species. This study aimed to describe the composition, abundance and temporal frequency of Anopheles species and to correlate these factors with precipitation, temperature and relative humidity. Methods The study was conducted in the District of Coração, State of Amapá, Brazil. Samples were collected monthly during three consecutive nights, from 6:00 PM to 10:00 PM, from December 2010 to November 2011. In addition, four 12-hour collections (i.e., 6:00 PM to 6:00 AM) were performed during this period. Results A total of 1,230 Anopheles specimens were collected. In the monthly collections, Anopheles darlingi was the predominant species, followed by An. braziliensis and An. albitarsis s.l., whereas An. darlingi, An. peryassui and An. braziliensis were the most frequent species collected in the 12-hour collections. The greatest number of anophelines was collected in September (the dry season). The highest frequency of anophelines was observed for An. darlingi during September, when there were the least rainfalls of the year, along with lower relative humidity and higher temperatures. There was little variation in the abundance of this species in other months, with the exception of slight increases in February, July and August. Conclusions The major malaria vectors, An. darlingi and An. albitarsis s.l. (likely An. marajoara), were the most abundant species collected in the study area. Consequently, prevention and control measures should be taken to prevent malaria outbreaks in the District of Coração. .

Copaifera multijuga ethanolic extracts, oil-resin, and its derivatives display larvicidal activity against Anopheles darlingi and Aedes aegypti (Diptera: Culicidae)

Copaifera spp. is a common tree species found in the tropical region of Latin America, popularly known as copaiba or pau-d'alho. Oil-resin from different Copaifera species and its components present several biological activities such as antimicrobial, anti-inflammatory, antioxidant and insecticidal, including larvicidal activity against mosquitoes. Thus, bark and leaf ethanolic extracts, oil-resin, essential oil and alepterolic acid from Copaifera multijuga Hayne, Fabaceae, were tested as larvicides against the main malaria vector in the north of Brazil, Anopheles darlingi and also Aedes aegypti, the dengue vector. A. darlingi larval mortality was significantly higher than A. aegypti for most tested compounds. Bark and leaf extracts resulted in lower Lethal Concentrations (LC50) values for A. darlingi, 3 and 13 ppm, respectively, while the essential oil provided the lowest LC50 value for A. aegypti, 18 ppm. Despite of that, the lowest LC values were from the alepterolic acid for both species, i.e. 0.9 and 0.7 ppm for A. darlingi and A. aegypti, respectively.

Larval control of Anopheles (Nyssorhinchus) darlingi using granular formulation of Bacillus sphaericus in abandoned gold-miners excavation pools in the Brazilian Amazon Rainforest

INTRODUCTION: Use of a Bacillus sphaericus based mosquito larvicide was evaluated as an intervention for malaria vector control at a mining site in Amapá, Brazil. Impacts on larval and adult densities of the primary vector Anopheles darlingi were measured over the course of a 52 week study period. METHODS: In Calçoene, State of Amapá, gold mining activity occurs in 19 mining sites in gold-miners of Lourenço. Large pools are formed in mining sites and naturally colonized by Anopheles darlingi. During one year, the impact of applications of VectoLex(r) CG to these larval sources was evaluated. Applications of 20kg/ha were made as needed, based on 10 immature (3rd, 4th instars and pupae) surveillance of health and established thresholds. RESULTS: One hundred percent initial control was observed 48h after each treatment. The pools received from 2-10 (5.3±1.6) treatments during the year. The average re-treatment interval in productive pools was 9.4±4.3 weeks. During weeks 3-52 of the study, mean density of late stage larvae was 78% and pupae were 93% lower in the treated pools than in untreated pools (p< 0.0001, n=51) while reduction of adult mosquitoes was 53% in comparison to the untreated area during the last five months of the study, which were the rainy season (p<0.001). CONCLUSIONS: VectoLex(r) CG reduced immature Anopheles darlingi infestation levels during the entire study period, and reduced adult mosquito populations during the rainy season. .

Malaria entomological risk factors in relation to land cover in the Lower Caura River Basin, Venezuela

To explore the effects of deforestation and resulting differences in vegetation and land cover on entomological parameters, such as anopheline species composition, abundance, biting rate, parity and entomological inoculation rate (EIR), three villages were selected in the Lower Caura River Basin, state of Bolívar, Venezuela. All-night mosquito collections were conducted between March 2008-January 2009 using CDC light traps and Mosquito Magnet(r) Liberty Plus. Human landing catches were performed between 06:00 pm-10:00 pm, when anophelines were most active. Four types of vegetation were identified. The Annual Parasite Index was not correlated with the type of vegetation. The least abundantly forested village had the highest anopheline abundance, biting rate and species diversity. Anopheles darlingi and Anopheles nuneztovari were the most abundant species and were collected in all three villages. Both species showed unique biting cycles. The more abundantly forested village of El Palmar reported the highest EIR. The results confirmed previous observations that the impacts of deforestation and resulting changes in vegetation cover on malaria transmission are complex and vary locally.

Mosquito Anthropophily: implications on malaria transmission in the northern Brazilian Amazon

Seasonal variation of adults and larvae of anophelines was studied during 2003 and 2004 in Roraima State, located in the Northern region of Brazilian Amazon. Species diversity increased with distance of capture to human dwellings. Greater diversity was found in extradomiciliary collections than in peridomiciliary or intradomiciliary. A significant association between Anopheles darlingi Root and An. albitarsis (s.l.) Arribálzaga (Diptera: Culicidae) breeding sites and the proximity to human dwellings was observed. Malaria Sporozoite Antigen Panel Assay (VectestTM Malaria) indicated An. albitarsis s.l. as one of the local vectors in the studied area. In this study, an index to describe the anthropophilic behavior of each anopheline species is proposed.

Variabilidade genética em populações de Anopheles darlingi (Diptera: Culicidae) e relação ao comportamento da atividade de picar, analisada por RAPD / Genetic variability in populations of Anopheles darlingi (Diptera: Culicidae) and relationship to biting activity behavior as analyzed by RAPD

Duas populações naturais de Anopheles darlingi foram analisadas quanto aos padrões de variabilidade genética relacionados ao comportamento hematofágico, cujas coletas foram realizadas no intra, peri e extradomicíio, em dois municípios do Estado do Amazonas: Coari e Manaus. Os resultados evidenciaram amplo número de fragmentos polimórficos, bem como elevada variabilidade genética nessas populações. Na população de Coari, a porcentagem de locos polimórficos (P) e heterozigosidade (He) variou de 77,63% - 84,86% e 0,2851 0,3069, respectivamente, sendo a maior variabilidade genética detectada nas subpopulações do intradomicílio, e a menor nas do peridomicílio. A população de Manaus mostrou variabilidade genética similar a de Coari (P= 75% - 78,94% e He= 0,2732 0,2741), onde também foi detectada maior variabilidade genética no intradomicílio. Os dados de qui-quadrado (x²= 695,89; GL= 304; P < 0,001) e de F ST (F ST= 0,0775 ± 0,0072) foram significativos, indicando uma estruturação micro geográfica, decorrente de alguma redução no fluxo gênico. Esses resultados podem ser interpretados como sendo em resposta à pressão de seleção face aos inseticidas, que permanecem residuais nas paredes dos domicílios.

Two natural populations of Anopheles darlingi, collected in the intra, peri and extra domicile of two townships in the State of Amazonas, Coari and Manaus, were assayed as to their hematophagic behaviour-related genetic variability patterns. Findings revealed a large number of polymorphic fragments as well as high genetic variability in these populations. Polymorphic loci rate (P) and heterozygosity (He) in the Coari population varied between 77.63% - 84.86% and 0.2851 0.3069, respectively, with the highest and lowest genetic variability being detected in the intra- and peri-domicile sub-populations, respectively. The Manaus population showed genetic variability and heterozygosity similar to those in Coari (P= 75% - 78.94% and He= 0.2732 0.2741), where higher genetic variability was detected in the intra-domicile as well. Chi-square data (x²= 695.89; GL= 304; P < 0.001) and F ST (F ST= 0.0775 ± 0.0072) were significant, indicating micro-geographic structuring resulting from some decreased gene flow. These findings point out the selective pressure response to the residual insecticide remaining on household walls after the entire neighbourhood had been sprayed with it during malaria control programs.

Espécies de Anopheles (Diptera, Culicidae) em municípios com risco e autoctonia de malária no estado de Goiás / Species of Anopheles (Diptera, Culicidae) collected in counties of risk and autochthonous cases of malaria in Goiás State, Brazil

Neste estudo, avaliou-se a frequência de espécies de Anopheles (Diptera, Culicidae) em municípios com risco e autoctonia de malária no estado de Goiás, no período de 1999 a 2006. Foram capturados 2.867 exemplares de 11 espécies de Anopheles em 26 municípios. A frequência das espécies Anopheles evansae, An. albitarsis, An. argyritarsis s.l., An. parvus, An. galvaoi e An. oswaldoi foi estatisticamente igual, porém significativamente maior do que a das espécies An. mediopunctatus, An. maculipes, An. braziliensis e An. kompi (p menor que 0,05). As espécies que apresentaram maior diversidade foram An. darlingi e An. argyritarsis. No período estudado, foram registrados 1.018 casos importados de malária e 23 casos autóctones. Dos casos autóctones diagnosticados, 21,7por cento foram causados por Plasmodium falciparum e 78,3por cento por P. vivax. Nos casos importados de malária, a frequência foi muito similar à dos autoctones, sendo de 27,2por cento e 72,8por cento para P. falciparum e P. vivax, respectivamente.

Mixed-function oxidases and esterases associated with cross-resistance between DDT and lambda-cyhalothrin in Anopheles darlingi Root 1926 populations from Colombia

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 percent 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 percent. 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.

Anopheles darlingi bionomics and transmission of Plasmodium falciparum, Plasmodium vivax and Plasmodium malariae in Amerindian villages of the Upper-Maroni Amazonian forest, French Guiana

French Guiana is one of the areas in South America most affected by malaria and where the disease has become a serious public health problem. In spite of this situation, little recent entomological data are available from the main localities where the disease occurs, even though they are crucial for development of an effective vector control strategy. A longitudinal entomological survey was carried out from March 2000-February 2002 in three Amerindian villages, namely Twenké, Taluène and Cayodé, located in the Amazonian forest of the Upper-Maroni area, to assess anopheline mosquitoes and malaria transmission dynamics. Anopheles darlingi (Diptera: Culicidae) was the most abundant mosquito species caught during the study. This efficient American malaria vector was active the entire year, but showed an evident peak of abundance during the main rainfall season, from April-June, with an average human biting rate of 255.5 bites per person per night. Parity rates were homogeneous all year, indicating no significant seasonal variability in female survival rates. Estimated vectorial capacity indices were higher during the rainy season, even though the risk of transmission was present throughout the year (VCI > 1). A total of 14 An. darlingi were found infected with Plasmodium falciparum, Plasmodium vivax or Plasmodium malariae. The annual circumsporozoite indices were 0.15, 0.14 and 0.05, and the entomological inoculation rates were 22.8, 27.4 and 14.4 infected bites per person per year in Twenké, Taluène and Cayodé, respectively. An. darlingiwas endo-exophagic and rather exophilic in these localities. The species was collected throughout the night but was more aggressive between 21:30-03:30 h and after 05:30 h. Parity rates were homogeneous during the entire night. Impregnated hammock and/or bed nets, coupled with the use of mosquito repellents, as well as the early treatment of malarial cases, appear to be the most suitable tools for fighting...

Population structure of the malaria vector Anopheles darlingi in Rondônia, Brazilian Amazon, based on mitochondrial DNA

Anopheles darlingi is the most important Brazilian malaria vector, with a widespread distribution in the Amazon forest. Effective strategies for vector control could be better developed through knowledge of its genetic structure and gene flow among populations, to assess the vector diversity and competence in transmitting Plasmodium. The aim of this study was to assess the genetic diversity of An. darlingi collected at four locations in Porto Velho, by sequencing a fragment of the ND4 mitochondrial gene. From 218 individual mosquitoes, we obtained 20 different haplotypes with a diversity index of 0.756, equivalent to that found in other neotropical anophelines. The analysis did not demonstrate significant population structure. However, haplotype diversity within some populations seems to be over-represented, suggesting the presence of sub-populations, but the presence of highly represented haplotypes complicates this analysis. There was no clear correlation among genetic and geographical distance and there were differences in relation to seasonality, which is important for malarial epidemiology.

A population genetics study of Anopheles darlingi (Diptera: Culicidae) from Colombia based on random amplified polymorphic DNA-polymerase chain reaction and amplified fragment lenght polymorphism markers

The genetic variation and population structure of three populations of Anopheles darlingi from Colombia were studied using random amplified polymorphic markers (RAPDs) and amplified fragment length polymorphism markers (AFLPs). Six RAPD primers produced 46 polymorphic fragments, while two AFLP primer combinations produced 197 polymorphic fragments from 71 DNA samples. Both of the evaluated genetic markers showed the presence of gene flow, suggesting that Colombian An. darlingi populations are in panmixia. Average genetic diversity, estimated from observed heterozygosity, was 0.374 (RAPD) and 0.309 (AFLP). RAPD and AFLP markers showed little evidence of geographic separation between eastern and western populations; however, the F ST values showed high gene flow between the two western populations (RAPD: F ST = 0.029; Nm: 8.5; AFLP: F ST = 0.051; Nm: 4.7). According to molecular variance analysis (AMOVA), the genetic distance between populations was significant (RAPD:phiST = 0.084; AFLP:phiST = 0.229, P < 0.001). The F ST distances and AMOVAs using AFLP loci support the differentiation of the Guyana biogeographic province population from those of the Chocó-Magdalena. In this last region, Chocó and Córdoba populations showed the highest genetic flow.

Man biting rate seasonal variation of malaria vectors in Roraima, Brazil

Malaria control has been directed towards regional actions where more detailed knowledge of local determinants of transmission is of primary importance. This is a short report on range distribution and biting indices for Anopheles darlingi and An. albitarsis during the dry and rainy season that follows river level variation in a savanna/alluvial forest malaria system area in the Northern Amazon Basin. Distribution range and adult biting indices were at their highest during the rainy season for both An. darlingi and An. albitarsis. During the rainy season the neighboring alluvial forest was extensively flooded. This coincided with highest rates in malaria transmission with case clustering near the river. As the river receded, anopheline distribution range and density decreased. This decrease in distribution and density corresponded to a malaria decrease in the near area. An exponential regression function was derived to permit estimations of An. darlingi distribution over specified distances. Anopheline spatio-temporal variations lead to uneven malaria case distribution and are of important implications for control strategies.

Vector bionomics and malaria transmission in the Upper Orinoco River, Southern Venezuela

A longitudinal epidemiological and entomological study was carried out in Ocamo, Upper Orinoco River, between January 1994 and February 1995 to understand the dynamics of malaria transmission in this area. Malaria transmission occurs throughout the year with a peak in June at the beginning of the rainy season. The Annual Parasite Index was 1,279 per 1,000 populations at risk. Plasmodium falciparum infections accounted for 64 percent of all infections, P. vivax for 28 percent, and P. malariae for 4 percent. Mixed P. falciparum/P. vivax infections were diagnosed in 15 people representing 4 percent of total cases. Children under 10 years accounted for 58 percent of the cases; the risk for malaria in this age group was 77 percent higher than for those in the greater than 50 years age group. Anopheles darlingi was the predominant anopheline species landing on humans indoors with a biting peak between midnight and dawn. A significant positive correlation was found between malaria monthly incidence and mean number of An. darlingi caught. There was not a significant relationship between mean number of An. darlingi and rainfall or between incidence and rainfall. A total of 7295 anophelines were assayed by ELISA for detection of Plasmodium circumsporozoite (CS) protein. Only An. darlingi (55) was positive for CS proteins of P. falciparum (0.42 percent), P. malariae (0.25 percent), and P. vivax-247 (0.1 percent). The overall estimated entomological inoculation rate was 129 positive bites/person/year. The present study was the first longitudinal entomological and epidemiological study conducted in this area and set up the basic ground for subsequent intervention with insecticide-treated nets.