Fluctuaciones estacionales y temporales de la densidad larvaria de Anopheles darlingi Root (Diptera: Culicidae) y familias de insectos asociados al hábitat en El Granzón, Parroquia San Isidro, municipio Sifontes del estado Bolívar, Venezuela / Seasonal and temporal fluctuations of larval densites of Anopheles darlingi Root (Diptera: Culicidae) and insects associated to the habitat in San Isidro Parish, Sifontes municipality, Bolívar state, Venezuela

Anopheles darlingi Root ha sido considerado en condiciones naturales como el principal vector de la malaria humana en América del sur y también en Venezuela, principalmente en los estados Bolívar y Amazonas, donde se produce el 90% de la malaria del país. Durante un mes (Junio de 1999) se realizaron muestreos en criaderos de mosquitos en siete localidades del área minera de San Isidro municipio Sifontes, estado Bolívar. Los sitios de muestreo fueron clasificados a priori en cuatro tipos de hábitat larvario: quebradas, lagunas, ríos, pantanos (herbáceo o arbóreo). En cada criadero se tomaron 30 muestras con un cucharón para colectar larvas de Anopheles. Simultáneamente al muestreo de larvas se midieron cuatro variables físico-químicas del criadero: pH, oxígeno disuelto, temperatura y profundidad del criadero. Asimismo, en un criadero de An. darlingi (quebrada con sombra), ubicado en la localidad de El Granzón, se llevó a cabo un estudio longitudinal, durante un año entre Julio de 1999 y Junio del 2000. En dicho criadero, se colectaron mensualmente larvas de An. darlingi e insectos acuáticos asociados. Las correlaciones entre la precipitación acumulada, la abundancia de estos insectos y la abundancia de larvas de An. darlingi, se establecieron mediante el análisis no paramétrico de correlación de Spearman (Spearman rank correlation). En el hábitat seleccionado, los resultados del análisis revelaron la presencia de una correlación negativa y significativa entre la abundancia de larvas de An. darlingi y la precipitación acumulada el mes anterior a la colecta. En esa misma localidad, la precipitación acumulada el mes anterior a la colecta, se correlacionó positivamente con la abundancia de la familia Naucoridae (Hemiptera). Asimismo, la abundancia de larvas de An. darlingi presentó una correlación negativa y significativa con la abundancia de la familia Naucoridae. En este hábitat (quebrada del Granzón), la densidad de larvas An. darlingi fue mayor en los meses de menor precipitación, aunque tanto en la época de menor precipitación como en la temporada lluviosa, hubo presencia de larvas de esta especie. Por otro lado, el criadero típico de An. darlingi, donde éste presentó su mayor abundancia y hubo presencia de larvas durante todo el año, fue clasificado como “Quebrada con sombra”. Esta presentó mucha sombra (90-100%), abundante materia orgánica sumergida o flotante (hojarasca, palitos, hojas, semillas), profundidad promedio de 65,22 cm, un pH promedio de 6,16, contenido medio de oxigeno disuelto de 6,40 g/L y una temperatura promedio del agua de 26ºC.

Anopheles darlingi Root has been considered under natural conditions as human malaria’s principal vector in South America. In Venezuela, Amazonas and Bolivar States, it is responsible for 90 % of malaria cases reported in the country. Field surveys and mosquito larvae sampling of mosquito breeding sites in mining areas, were carried out in seven localities of Sifontes county, Bolívar state during one month, between 2 and 29 June 1999. The breeding sites were a priori classified into four larval habitat categories: lagoons, streams, rivers and herbaceous swamps. At each breeding site, 30 dips for mosquito larvae samples were made. Simultaneously with mosquito larvae sampling, four selected variables of water were measured: temperature, dissolved oxygen, pH and water depth. On the other hand, a longitudinal study was carried out in the typical An. darlingi breeding site (shaded streams) in El Granzón (Sifontes county). Field surveys of mosquito larvae and aquatic insects were carried out in the same breeding site over a one-year period (July, 1999 to June, 2000). At this breeding site, Anopheles larvae and aquatic insects were collected monthly. During the study, 12 samples were taken from this larval habitat of An. darlingi. Seasonal and temporal variations of An. darlingi larvae and aquatic insects were determined. Relationships among the rain in the previous month, abundance of aquatic insects and abundance of An. darlingi larvae, were investigated using the Spearman nonparametric test (Spearman rank correlation). Results of the analysis revealed that the abundance of An. darlingi mosquito larvae was negatively correlated with the rainfall in the previous month. On the other hand, the results indicate that the abundance of An. darlingi larvae was negatively correlated with the abundance of the family Naucoridae (Hemiptera), and this family was positively correlated with the rainfall in the previous month. The typical An. darlingi larval habitat was classified into the category “streams shaded”. This streams were very shaded (90-100%), with a water depth of 65.22 cm, with abundant floating organic debris (dry foliage, leaves, trash, small stick), a pH of 6.16, dissolved oxygen of 6.40 g/L, and a water temperature of 26ºC.

Morphological aspect of the midgut of anopheles aquasalis (Curry, 1932) Insecta: Diptera / Aspecto morfológico del intestino medio de anopheles aquasalis (Curry, 1932) Insecta: Diptera

The midgut of adult female Anopheles aquasalis presents a narrow anterior or thoracic region and a distensible posterior or abdominal region constituted by the epithelium formed by a cell layer whose apical portion presents microvilli and the basal portion, a basal labyrinth. The thoracic region revealed heterogeneous cellular staining affinity mainly by the presence of acidic components. The ultrastructural aspect showed columnar cells with the presence of the vesicle, mitochondria, endoplasmic reticulum and secreting cells. The abdominal region of the midgut revealed an irregular epithelium whose cells presented a basophilic cytoplasm and acidophil granules. It was also found secreting and/or basal cells with narrow cytoplasm. The ultrastructural observation of this region demonstrated cells with evident nucleus, endoplasmic reticulum and mitochondria. Larger vesicles and small granules were found distributed throughout the cytoplasm. The basal lamina that supports the epithelium presented a generally irregular aspect and the muscle fibers have longitudinal and circular organization and were found separating the epithelium from the haemocel. This study will contribute to analyses on the vector mosquito-parasite interaction mechanism in this specimen.

La seccion media del intestino de la hembra de Anopheles aquasalis presenta una estrecha region anterior o toráxica y una region posterior o abdominal constituida por el epitelio formado por una camada de células cuya porcion apical presenta microvilosidades y la porcion basal presenta un laberinto basal. La region toráxica reveló afinidad de tintura celular principalmente para componentes acídicos. El aspecto ultra estructural mostró células columnares con la presencia de la vesícula, mitocondrias, retículo endoplasmático y células secretoras. La region abdominal del intestino medio reveló un epitelio irregular con células con citoplasma basófilo y granulos acidófilos. También se encontraron células secretoras y/o básales con citoplasma estrecho. La observacion ultra estructural de la region mostró células con núcleos, retículo endoplasmático y mitocondrias evidentes. Vesículas largas y granulos pequeños fueron encontrados distribuidos por todo el citoplasma. La lámina basal que apoya el epitelio presentó un aspecto irregular y las fibras musculares tienen organizacion longitudinal y circular y separan el epitelio del hemocele. Este estudio contribuirá al análisis del mecanismo de interaccion entre el mosquito y el parásito en este espécimen.

Anopheles aquasalis eggs from two Venezuelan localities compared by scanning electron microscopy

Anopheles (Nyssorhynchus) aquasalis, is the main coastal vector of malaria from northeastern Venezuela to southeastern Brazil. Several authors have argued that An. aquasalis is a high polymorphic species while others indicated that it is a complex of closely related species. This investigation compared the morphology of An. aquasalis eggs from Sinamaica (Zulia State) and Yaguaraparo (Sucre State), the west and east of Venezuela, respectively. We were able to separate eggs from the two localities using discriminant analyses based on ratios and percentages of anterior and posterior tubercles measured by scanning electron microscopy. The results of this work suggest that An. aquasalis has high intraspecific variation.

Description of the immature stages of Anopheles (Nyssorhynchus) rondoni (Neiva & Pinto) (Diptera: Culicidae)

The larval and pupal stages of Anopheles (Nyssorhynchus) rondoni (Neiva and Pinto) (Albimanus Section) are fully described and illustrated for the first time. The larval stage is similar to An. (Nys.) strodei Root. It can be recognized by the following combination of characteres: clypeal index, 1.6-2.9; single, aciculate setae 2,3-C; seta 3-C 0.5-0.7 the lenght of 2-C; setae 1,2-P rarely sharing a common tubercle; seta 1-P with narrow leaflets. The pupal stage is distinguished from other Nyssorhynchus by having setae 1-IV-VII and 5-V-VII branched. Only minor variation was found in setal counts between specimens from Peixoto de Azevedo, State of Mato Grosso and Bocaina, State of Sao Paulo, Brazil.

Egg structures of Anopheles fluminensis and Anopheles shannoni

Eggs of two species belonging to the Arribalzagia Series of the Laticorn Section of Anopheles (Anopheles) collected in Brazil are described from scanning electron micrographs. The An. fluminensis egg is long with shallow floats displaced far dorsally. The narrow deck region is overlain by a frill modified into prominent ridges that are nearly continuous to both ends of the egg. Slightly opened decks at both poles contain an average of four lobed tubercles. Polygonal, plastron-type chorionic cells cover the lateral and dorsal surfaces. The egg of An. shannoni is unique in possessing 22-27 fingerlike filaments that project with regular spacing from each of its massive floats. These filaments and their bases are highly perforated and are believed to trap air and support flotation of the egg with the dorsal surface up, contrary to the usual orientation for anophelines. The eggs are compared with those of related species bearing similar structures, notably An. fluminensis with An. mediopunctatus s.s. and An. shannoni with An. peryassui.

Establishment and characterization of a cell line from the mosquito Anophles albimanus (Diptera: Culicidae)

A new cell line designated LSB-AA695BB, was established from embryos of the mosquito Anopheles albimanus. The primary culture was initiated in April, 1995, and the first passage was made 48 days later. Serial subcultures of the cells have been carried through 90 passages from April 1995 to February 1996. The cells were grown at 28ºC in MK/VP12 medium, supplement with 20 per cent fetal bovine serum; the pH tolerance ranged between 6.8 to 7.0. The cells have also been adapted to MM/Vp12 medium under the same pH, temperature and serum concentration. The majority of the cells were a fibroblast-type. Isoenzyme characterization showed a pattern similar to that of An. albimanus pupae and adults but distinct from Ae. taeniorhynchus and Ae. albopictus (C6/36) mosquito cell lines. The culture was shown to be free of mycoplasma, bacteria and fungi. Microsporidia contamination of transovarial transmission was controlled with 6.0 µg/ml of albendazole.

Initiation of primary cell cultures from embryos of the mosquitoes Anopheles albimanus and Aedes taeniorhynchus (Diptera: Culicidae)

Primary cell cultures were obtained from eggs of Anopheles albimanus and Aedes taeniorhynchus mosquitoes, vectors of human malaria and of Venezuelan equine encephalitis virus, respectively. The cellular growth of the An. albimanus cells began four weeks after explanting the embryonic tissues in MK/VP12 medium, supplemented with 15 por cento fetal bovine serum. The culture showed heterogeneous cellular morphology. With regard to the Ae. taeniorhynchus culture, growth occurred three weeks after initiating the culture in MM/VP12 medium. The majority of cells were small and round. Karyotypes were examined in the latter species.