Assessment of Culex pipiens bioforms in the world's southernmost distribution limit

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Gonotrophic discordance in Culex quinquefasciatus (Diptera: Culicidae) in the city of São Paulo, Brazil

Abstract INTRODUCTION: This study aimed to assess the occurrence of gonotrophic discordance in females of Culex quinquefasciatus in São Paulo, Brazil. METHODS: Resting females were collected monthly for 8 months. Females of Cx. quinquefasciatus were identified, and their midgut and ovaries were dissected. RESULTS: Two hundred females were dissected, out of which, 27.5% were nulliparous and 57% were parous. Most females had no blood in the midgut, but gonotrophic discordance was found in 21% females. CONCLUSIONS: Females of Cx. quinquefasciatus showed a high parity rate and gonotrophic discordance, which could favor the vector capacity of this species.

Influence of climatic variables on the Aedes aegypti and Culex quinquefasciatus populations in Mato Grosso, Brazil

Abstract INTRODUCTION: Aedes aegypti and Culex quinquefasciatus are vector species responsible for the transmission of important arboviruses. METHODS: Adult mosquitoes were collected in the urban areas of four municipalities in Mato Grosso within 1 year. RESULTS: A total of 19,110 mosquitoes were collected. Among them, 16,578 (86,8%) were C. quinquefasciatus (44% female and 56% male); 2,483 (13%), A. (Stegomyia) aegypti (54% female and 46% male); and 49 (0,30%), from the genus Psorophora, Anopheles, Coquilettidia, and Sabethes. A significant correlation was observed between the number of mosquitoes from all species and dew point (female mosquitoes, p = 0.001; male mosquitoes, p = 0.001). CONCLUSIONS: The results of this study may be used as environmental indicators of mosquito populations.

Distribution of the members of the Pipiens Assemblage in the sympatric area from Argentina: which is where and when?

Given their medical and veterinary relevance, the members of the Pipiens Assemblage are a worldwide target of ecological research. The distribution of Culex pipiens s.s. and Cx. quinquefasciatus converge in Buenos Aires, Argentina, where hybrids have been detected. Each member of the assemblage exhibits a distinct eco-physiological behaviour that can affect its efficiency in pathogen transmission. Our aim was to identify the environmental drivers for the spatio-temporal distribution of each member, focusing on latitudinal and urbanisation gradients. Immatures of mosquitoes were surveyed in artificial containers found within 11 public cemeteries, raised up to the adult stage and identified by their male genitalia. The distribution of each member was associated with the environment in a Generalized Linear Model. The variable accounting for most of the heterogeneity was latitude; Cx. quinquefasciatus was collected more frequently at northern cemeteries, whereas Cx. pipiens and hybrids were more likely at the southern extreme. The urbanisation gradient was also associated with the occurrence of Cx. quinquefasciatus and hybrids at the high and low end, respectively. Other relevant variables were cemetery total area, the proportion with graves and the presence of plastic flowers in the containers. The spatial distribution of the members of the Pipiens Assemblage within the sympatric region in South America is driven by environmental features. The information presented herein provides essential baseline data for surveillance programs and control activities.

The behaviour of mosquitoes in relation to humans under holed bednets: the evidence from experimental huts

The physical integrity of bednets is a concern of national malaria control programs, as it is a key factor in determining the rate of replacement of bednets. It is largely assumed that increased numbers of holes will result in a loss of protection of sleepers from potentially infective bites. Experimental hut studies are valuable in understanding mosquito behaviour indoors, particularly as it relates to blood feeding and mortality. This review summarises findings from experimental hut studies, focusing on two issues: (i) the effect of different numbers or sizes of holes in bednets and (ii) feeding behaviour and mortality with holed nets as compared with unholed nets. As might be expected, increasing numbers and area of holes resulted in increased blood feeding by mosquitoes on sleepers. However, the presence of holes did not generally have a large effect on the mortality of mosquitoes. Successfully entering a holed mosquito net does not necessarily mean that mosquitoes spend less time in contact with the net, which could explain the lack in differences in mortality. Further behavioural studies are necessary to understand mosquito behaviour around nets and the importance of holed nets on malaria transmission.

Residential characteristics aggravating infestation by Culex quinquefasciatus in a region of Northeastern Brazil / Características agravantes por infestação residencial de Culex quinquefasciatus, em Olinda, PE

OBJECTIVE: Analyse how basic sanitation conditions, water supply and housing conditions affect the concentration of Culex quinquefasciatus METHODS: Populations of C. quinquefasciatus in 61 houses in the municipality of Olinda, PE, were monitored between October 2009 and October 2010. Observations were carried out in homes without the presence of preferred breeding sites in order to identify characteristics that may be aggravating factors for the development of the mosquito. Five aggravating factors were analysed: vegetation cover surrounding the home, number of residents/home, water storage, sewage drainage and water drainage. These characteristics were analysed in terms of presence or absence and as indicators of the degree of infestation, which was estimated through monitoring the concentration of eggs (oviposition traps - BR-OVT) and adults (CDC light traps). RESULTS: Sewage drainage to a rudimentary septic tank or to the open air was the most frequent aggravating factor in the homes (91.8%), although the presence of vegetation was the only characteristic that significantly influenced the increase in the number of egg rafts (p = 0.02). The BR-OVT achieved positive results in 95.1% of the evaluations, with the presence of at least one egg raft per month. A total of 2,366 adults were caught, with a mosquito/room/night ratio of 32.9. No significant difference was found in the number of mosquitoes caught in the homes. CONCLUSIONS: Although the sanitation and water supply influence the population density of C. quinquefasciatus, residence features that are not usually considered in control measures can be aggravating factors in sustaining the mosquito population.

OBJETIVO: Analisar como as condições de saneamento básico, abastecimento de água e habitações afetam a densidade de Culex quinquefasciatus. MÉTODOS: Monitorou-se a população de C. quinquefasciatus em 61 residências do município de Olinda, PE, de outubro de 2009 a outubro de 2010. As observações foram realizadas em residências sem a presença de criadouros preferenciais, para identificar características que contribuíssem como agravantes para o desenvolvimento do mosquito. Cinco características agravantes foram analisadas: cobertura vegetal no peridomicílio, número de moradores por residência, armazenamento de água, escoamento de esgoto, escoamento de água. Essas características foram avaliadas quanto à presença ou ausência e como indicadores de níveis de infestação, estimados por monitoramento da densidade de ovos (armadilhas de oviposição BR-OVT) e adultos (armadilhas luminosas do tipo CDC). RESULTADOS: O escoamento de esgoto para fossa séptica/rudimentar e a céu aberto foi o mais frequente nas residências (91,8%), embora apenas a presença de vegetação tenha influenciado significativamente no aumento de jangadas (p = 0,02). As BR-OVT apresentaram-se positivas em 95,1% das avaliações, com presença de pelo menos uma jangada/mês. Foram capturados 2.366 espécimes adultos, com relação mosquito/quarto/noite de 32,9, sem diferença significativa no número de mosquitos capturados nas residências. CONCLUSÕES: Embora as condições de saneamento e de abastecimento de água influenciem na densidade populacional de C. quinquefasciatus, características da residência que normalmente não são consideradas nas medidas de controle podem ser fatores agravantes na manutenção da população de mosquito.

Bionomics of Culex quinquefasciatus within urban areas of Rio de Janeiro, Southeastern Brazil / Bionomia de Culex quinquefasciatus em áreas urbanas no Rio de Janeiro, RJ / Bionomía de Culex quinquefasciatus en áreas urbanas en Rio de Janeiro, Brasil

OBJECTIVE: To evaluate density, parity rates, daily survival and longevity of natural populations of Culex quinquefasciatus in three neighborhoods with distinct socio-economic and infrastructure profiles. METHODS: Mosquito collections of the Culex quinquefasciatus species were performed weekly during two four month periods, from August to November 2008 (spring) and March to June 2009 (fall), in a favela (slum), a suburban area and a middle class area of Rio de Janeiro, Southeastern Brazil. Collections were performed with backpack aspirators, in 20 randomly selected houses in each area per week, during 15-20 minutes per house. Ovaries were removed from captured females and classified as initial, intermediary or final stage. Furthermore, females were dissected for determination of parity based on the condition of the tracheal system. Mosquito survival rate and longevity were estimated on a per month basis for each neighborhood. RESULTS: We collected a total of 2,062 Culex quinquefasciatus, but monthly vector density was not correlated with temperature and rainfall. We dissected the ovaries of 625 Culex quinquefasciatus, and overall, there was a higher proportion of nulliparous females during the dryer months, while gravid females were more frequent in rainy months. In the middle class neighborhood, the parity rate reached up to 93.75% with survivorship of 0.979. Lower parity and survival rates were obtained in the suburban area (as low as 36.4% parity and 0.711 daily survival). Up to 84.7% of Culex quinquefasciatus females could survive the eight day period needed to complete West Nile Virus incubation. CONCLUSIONS: The survival rate of Culex quinquefasciatus varied significantly between the neighborhoods. This suggests that vectorial capacity and disease transmission risk may vary greatly between different urban areas, which is potentially useful information for vector control programs.

OBJETIVO: Avaliar densidade, taxa de paridade, sobrevivência diária e longevidade de populações naturais de Culex quinquefasciatus de três localidades com diferentes perfis socioeconômicos e de infraestrutura. MÉTODOS: Mosquitos da espécie Culex quinquefasciatus foram coletados semanalmente em dois períodos de quatro meses, de agosto a novembro de 2008 e de março a junho de 2009, em uma comunidade, uma área de subúrbio e um bairro de classe média no Rio de Janeiro, RJ. As coletas foram realizadas com o auxílio de aspiradores costais em 20 domicílios, aleatoriamente selecionados por semana e por área, durante 15-20 minutos por domicílio. As fêmeas capturadas tiveram os ovários removidos e classificados em estágios inicial, intermediário e final. Adicionalmente, as fêmeas foram dissecadas para determinação da paridade de acordo com as condições do sistema traqueal. A taxa de sobrevivência e a longevidade das fêmeas foram estimadas por mês, para cada localidade. RESULTADOS: Foram coletados 2.062 Culex quinquefasciatus, porém a densidade mensal deste vetor não apresentou correlação com temperatura e precipitação. Dissecamos os ovários de 625 Culex quinquefasciatus e obtivemos maior proporção de fêmeas nulíparas durante os meses mais secos, enquanto fêmeas grávidas foram mais frequentes nos meses chuvosos. A taxa de paridade foi de até 93,75% no bairro de classe média, com sobrevivência de 0,979. Menores valores de paridade e sobrevivência foram obtidos no subúrbio (começando em 36,4% de paridade e 0,711 de sobrevivência diária). Até 84,7% das fêmeas de Culex quinquefasciatus poderiam sobreviver ao período de oito dias, necessário para completar o período de incubação do vírus da febre do Nilo Ocidental. CONCLUSÕES: A taxa de sobrevivência de Culex quinquefasciatus variou significativamente entre os bairros, o que sugere que a capacidade vetorial e o risco de transmissão de doenças podem variar entre diferentes áreas urbanas, informação relevante para o planejamento dos programas de controle de vetores.

OBJETIVO: Evaluar densidad, tasa de paridad, sobrevivencia diaria y longevidad de poblaciones naturales de Culex quinquefasciatus de tres localidades con diferentes perfiles socioeconómicos y de infraestructura. MÉTODOS: Mosquitos de la especie Culex quinquefasciatus fueron colectados semanalmente en dos períodos de cuatro meses, de agosto a noviembre de 2008 y de marzo a junio de 2009, en un barrio, un área de suburbio y una urbanización de clase media en Rio de Janeiro, Litoral Sudeste de Brasil. Las colectas se realizaron con ayuda de aspiradores costales en 20 domicilios, aleatoriamente seleccionados por semana y por área, durante 15-20 minutos por domicilio. A las hembras capturadas se les retiraron los ovarios y clasificaron en fases inicial, intermediario y final. Adicionalmente, las hembras fueron diseccionadas para determinar la paridad de acuerdo con las condiciones del sistema traqueal. La tasa de sobrevivencia y la longevidad de las hembras fueron estimadas por mes para cada localidad. RESULTADOS: Se colectaron 2.062 Culex quinquefasciatus, sin embargo, la densidad mensual del vector no presentó correlación con la temperatura y precipitación. Se diseccionaron los ovarios de 625 Culex quinquefasciatus y se obtuvo mayor proporción de hembras nulíparas durante los meses más secos, mientras que las hembras grávidas fueron más frecuentes en los meses de lluvia. La tasa de paridad alcanzó el 93,75% en la urbanización de clase media, con sobrevivencia de 0,979. Menores valores de paridad y sobrevivencia se obtuvieron en el suburbio (comenzando en 36,4% de paridad y 0,711 de sobrevivencia diaria). El 84,7% de las hembras de Culex quinquefasciatus podrían sobrevivir al período de ocho días, necesario para completar el período de incubación del virus de la fiebre del Oeste del Nilo. CONCLUSIONES: La tasa de sobrevivencia de Culex quinquefasciatus varió significativamente entre las urbanizaciones, sugiriendo que la capacidad vectorial y el riesgo de transmisión de enfermedades pueden variar entre diferentes áreas urbanas, información relevante para la planificación de los programas de control de vectores.

Tire-breeding mosquitoes of public health importance along an urbanisation gradient in Buenos Aires, Argentina

Used vehicle tires are a source of mosquito vectors and a means of their introduction and expansion. With the aim of assessing the effects of urbanisation on the main mosquito vectors in temperate Argentina, the infestation levels of Aedes aegypti (L.) and Culex pipiens L. were studied in used tires from highly urbanised cities to low-urbanised small towns in Buenos Aires. Immatures of both species accounted for 96 percent of the 9,722 individuals collected; the total individuals collected represented seven species. The percentage of water-filled tires containing mosquitoes [container index (CI)] was 33 percent and the percentage of infested sites [site index (SI)] was 65.2 percent. These indexes decreased significantly from low to high urbanisation levels for both mosquito species. The relative abundance (RA) of Ae. aegypti immatures was slightly higher toward large cities, but showed no difference for Cx. pipiens. The CI of shaded tires was significantly higher than the CI of exposed tires for both mosquito species. There was no difference in RA values between shaded and sunlit tires. The CI and the SI were highest during the summer across the urbanisation levels, except for Cx. pipiens, which continued to increase during the autumn in small towns. Results related to urbanisation gradient, sunlit exposure and seasonality are discussed.

Development of a controlled release formulation of an indigenous insect growth regulator, DPE-28, a substituted diphenylether, for controlling the breeding of Culex quinquefasciatus.

Background & objectives: DPE-28, a substituted diphenyl ether (2,6-ditertiarybutyl phenyl-2’,4’-dinitro phenyl ether) was reported to exhibit promising insect growth regulating activity against Culex quinquefasciatus, the vector of lymphatic filariasis. A controlled release formulation (CRF) of DPE-28 has been developed to control Cx. quinquefasciatus in its breeding habitats. Toxicity of DPE-28, safety to non-target mosquito predators and the release profile of the CRF of DPE-28 are studied and discussed. Methods: The acute oral and dermal toxicity was tested in male and female Wistar rats as per the Organization for Economic Cooperation and Development (OECD) guidelines 425 and 402 respectively. The toxicity of DPE-28 to non-target predators was tested as per the reported procedure from this laboratory. The CRF of DPE-28 was prepared by following the reported procedure developed at this laboratory earlier. The concentration of DPE-28 released from the CRF was monitored by HPLC by constructing a calibration graph by plotting the peak area in the Y-axis and the concentration of DPE-28 in the X-axis. Results: DPE-28 has been tested for acute oral toxicity and found to be moderately toxic with LD50 value of 1098 mg/kg body weight (b.w). The results of the acute dermal toxicity and skin irritation studies reveal that DPE-28 is safe and non-irritant. DPE-28 when tested at 0.4 mg/litre against non-target mosquito predators did not produce any mortality. The release profile of the active ingredient DPE-28 from the CRF by HPLC technique showed that the average daily release (ADR) of DPE-28 ranged from 0.07 to 5.0 mg/litre during first four weeks. Thereafter the matrix started eroding and the ADR ranged from 5 to 11 mg/litre during the remaining 5 wk. The cumulative release of active ingredient showed that > 90 per cent of the active ingredient was released from the matrix. Interpretation & conclusions: The controlled release matrix of DPE-28 was thus found to inhibit the adult emergence (>80%) of Cx. quinquefasciatus for a period of nine weeks. The CRF of DPE-28 may play a useful role in field and may be recommended for mosquito control programme after evaluating the same under field conditions.

Spatio-temporal variations in adult density, abdominal status & indoor resting pattern of Culex quinquefasciatus Say in Panaji, Goa, India.

Background & objectives: Goa is one of the filariasis endemic states of India. However, information on density pattern and resting behavior of Culex quinquefasciatus Say, the principal vector of filariasis in Goa is lacking. Therefore, current longitudinal study was undertaken to investigate these aspects. Methods: Panaji was divided into six zones and a total of 240 man hours were spent in 60 fixed catching sites to collect the adult Cx. quinquefasciatus mosquitoes on fortnightly basis from indoor resting sites during 2005-06. The female mosquitoes were classified as unfed, fed, semi-gravid and gravid to ascertain the resting behavior of Cx. quinquefasciatus adults. The data were analysed to evaluate the spatio-temporal variations in adult density, abdominal status and indoor resting sites and linked to meteorological variables like temperature, relative humidity, rainfall and number of rainy days. Results: Cx. quinquefasciatus adults were prevalent perennially in Panaji with highest per man hour density of females (48.6) in February and the lowest density (6.6) in September. Monthly variations in the densities between different months was significant (F=15.3; P<0.05). Rainfall significantly influenced the population of Cx. quinquefasciatus (t=2.63; P<0.05). Fed group and semi-gravid group showed a strong correlation with the relative humidity (P<0.05), rain fall (P<0.05) and number of rainy days (P<0.05). 62.4 per cent of females and 65.1 per cent of males preferred to rest on hanging objects. Spatio-temporal variations in the number of Cx. quinquefasciatus females and males resting on different sites and also the variations in different sites (P<0.05) were significant. Interpretation & conclusion: The density of female Cx. quinquefasciatus encountered in all the months was higher than the estimated tolerated level of density of 34 per ten man hours up to which there is no risk of filariasis transmission. The strong correlation between the abdominal conditions and relative humidity, rainfall and number of rainy days imply that these meteorological variables significantly influenced the feeding and fecundity of the species. 85.3 per cent of the indoor resting population comprising of fed, semi-gravid and gravid females confirmed the endophilic nature of the species. The preferential resting behavior of both females and males on hanging objects suggest that use of insecticide treated long-lasting bed nets as personal protective measure can be exploited to reduce the density of the vector species.

Culex quinquefasciatus vitellogenesis: morphological and biochemical aspects

The vitellogenic process in Culex quinquefasciatus, which is triggered by a blood meal, involves the synthesis, distribution and storage of the nutrients necessary for embryo development. The fat body of an adult female Cx. quinquefasciatus revealed two cell types: large trophocytes and small, eosinophilic, "oenocyte-like" cells, which show no morphological changes throughout the gonotrophic cycle. Trophocytes, which only begin to synthesise vitellogenin (Vg) 12 h post-blood meal (PBM), undergo a series of morphological changes following engorgement. These changes include the expansion of the rough endoplasmic reticulum (RER) and Golgi complex, which are later destroyed by autophagosomes. At 84 h PBM, trophocytes return to their pre-engorgement morphology. The ovarian follicles of non-blood-fed Cx. quinquefasciatus contain a cluster of eight undifferentiated cells surrounded by follicular epithelium. After engorgement, the oocyte membrane facing the perioocytic space increases its absorptive surface by microvilli development; large amounts of Vg and lipids are stored between 24 and 48 h PBM. Along with yolk storage in the oocyte, follicular cells exhibit the development of RER cisternae and electron-dense granules begin to fill the perioocytic space, possibly giving rise to endochorion. Later in the gonotrophic cycle, electron-dense vesicles, which are possible exochorion precursors, fuse at the apical membrane of follicular cells. This fusion is followed by follicular cell degeneration.

Análise comparativa dos ritmos de atividade locomotora e expressão circadiana de Aedes aegypti e Culex quinquefasciatus / Comparative analysis of the rhythms of locomotor activity and circadian expression of Aedes aegypti and Culex quinquefasciatus

A grande maioria dos seres vivos complexos apresenta um relógio endógeno, conhecido como relógio circadiano, responsável por dirigir as oscilações rítmicas de fisiologia e comportamento dentro de um período de aproximadamente 24 horas. Em insetos, as bases genéticas deste marcapasso têm sido elucidadas em Drosophila melanogaster. Diversos loci já foram identificados e o mecanismo molecular regulando o relógio circaiano consiste de alças regulatórias interligadas que controlam a expressão rítmica de muitos genes. Muitas espécies de mosquitos são vetores de doenças. Elas exibem um variedade de padrões de atividade e hematofagia, de diurnos a crepusculares e noturnos e estes ritmos são importantes para a dinâmica da transmissão de doenças. Entretanto, apesar da sua importância epidemiológica, pouco se sabe quanto à genética molecular do relógio circadiano que controla seus ritmos de atividade. Nosso grupo tem estudado as bases moleculares do relógio circadiano em duas espécies de mosquitos, Aedes aegypti e Culex quinquefasciatus. Ambos são importantes vetores de doenças tropicais, mas com diferentes padrões de atividade. Ae. aegypti é o vetor diurno da Dengue e da Febre amarela, enquanto Cx. quinquefasciatus é o vetor noturno da Filariose e da Filariose e da Febre do Oeste do Nilo. Análises preliminares indicam uma conservação dos padrões de expressão entre as duas espécies em alguns dos mais importantes genes do relógio em claro-escuro e escuro constante. Entretanto, nós achamos diferenças na expressão do gene cryptochrome2 (cry2), um ortólogo dos genes codificando criptocromos de mamíferos e que foi encontrado em muitos insetos, mas que não está presente em Drosophila. Nós sugerimos que cry2 pode estar envolvido no controle dos padrões de atividade de Ae. aegypti e Cx. quinquefasciatus, e propusemos um modelo para explicar as diferenças na expressão de cry2. Nós também estudamos a expressão circadiana dos principais genes de relógio, além dos ritmos de atividade locomotora destas duas espécies em ciclos de temperatura. Observamos que ambas são arrastadas pela temperatura e mostram diferenças entre seus comportamentos de atividade. Em ciclos de temperatura, a atividade locomotora de Ae. aegypti é mais restrita a termofase, enquanto Cx. quinquefasciatus apresenta sua atividade mais restrita a criofase. Além disso, após o arrastamento em ciclos de claro-escuro, Ae. aegypti mostrou um padrão transiente de atividade por alguns dias em escuro constante com ciclos de temperatura, enquanto Cx. quinquefasciatus permaneceu estável nesta condição. Também foram observadas, em ciclos de temperatura, algumas diferenças espécies-específicas nos padrões de expressão de cycle e cry2. Finalmente, nós observamos diferenças na fase da expressão circadiana de Ae. aegypti em ciclos de temperatura e escuro constante entre mosquitos criados com uma combinação de ciclos de claro-escuro e de temperatura com mosquitos criados em ciclos de claro-escuro com temperatura constante. Isto sugere um importante papel do desenvolvimento na determinação dos padrões de expressão circadiana de insetos adultos submetidos a oscilações de temperatura.

Occurrence of apocrine secretion in the larval gut epithelial cells of Aedes aegypti L., Anopheles albitarsis Lynch-Arribálzaga and Culex quinquefasciatus say (Diptera: Culicidae): a defense strategy against infection by Bacillus sphaericus Neide? / Ocorrência de secreção apócrina nas células epiteliais do intestino de larvas de Aedes aegypti L., Anopheles albitarsis Lynch-Arribálzaga e Culex quinquefasciatus say (Diptera: Culicidae): um mecanismo de defesa contra infecção causada por Bacillus sphaericus Neide?

Cell hypertrophy was the first reaction of the gut epithelial cells of Aedes aegypti (L.), Anopheles albitarsis (Lynch-Arribálzaga) and Culex quinquefasciatus (Say) to the toxins of strains 2362 and S1116 of Bacillus sphaericus, as cells had an increase of intracellular secretory activity. Soon after the cell hypertrophy developed, vesicles were formed at the cell apical portion, which detached with the plasma membrane, characterizing a type of apocrine secretion like. The first pathway of contamination of the mosquito larvae by these bacteria is through the gut, by feeding. Depending on the species of Culicidae and on the bacterial strain used, the hypertrophy of the gut epithelium occurred between 5 and 15 min after exposure to the contaminated environment. The second aspect observed after hypertrophy was the increase in apocrine secretion. The basophilic vesicles that detached from the cells remained between the peritrophic membrane and the gut lumen, such vesicles were filled with material of unknown nature. The gut posterior region showed secretory activity in both control and treated larvae, being much more intense in bacteria-exposed larvae. There were remarkable differences in the epithelial cell reaction according to the toxins of the two bacterial strains, but C.quinquefasciatus was the most susceptible. Differences in the gut cell reactions to the toxins produced by the two bacterial strains are discussed.

Observou-se hipertrofia das células do epitélio intestinal de Aedes aegypti (L.), Anopheles albitarsis (Lynch-Arribálzaga) e Culex quinquefasciatus (Say) devido ao aumento da atividade secretora intracelular como primeira reação às toxinas das linhagens 2362 e S1116 de Bacillus sphaericus (Neide). Após a hipertrofia epitelial, formaram-se vesículas na porção apical das células, as quais eram compostas de fragmentos de membrana plasmática contendo material de natureza desconhecida em seu interior, caracterizando um tipo de secreção apócrina. A via de contaminação das larvas dos mosquitos por essas bactérias é pelo intestino, através da alimentação. Dependendo da espécie de Culicidade e da linhagem bacteriana utilizada, a hipertrofia do epitélio ocorreu entre 5 a 15 min após a exposição das larvas ao meio contaminado. O segundo aspecto observado no processo de contaminação foi o aumento da atividade de secreção apócrina. As vesículas basófilas que se desprendiam das células permaneciam entre a membrana peritrófica e o lúmen intestinal. Observou-se atividade secretora tanto no grupo controle como no experimental, porém muito mais intensa no grupo experimental. Os Culicidae estudados apresentaram diferenças marcantes nas respostas às toxinas das bactérias utilizadas, sendo C. quinquefasciatus a espécie mais suscetível. As diferenças de reações das células em relação às toxinas produzidas pelas duas linhagens bacterianas são discutidas.

Vulnerability of the mosquito larvae to the guppies (Poecilia reticulata) in the presence of alternative preys.

BACKGROUND & OBJECTIVES: The predatory potential of the larvivorous fishes can be affected by the presence of alternative preys. In the present study the predation pattern of the sewage dwelling Poecilia reticulata (Peters 1872) on the larvae of Culex quinquefasciatus Say 1823 (Diptera: Culicidae) was evaluated in the presence of alternative preys. METHODS: The predation of Cx. quinquefasciatus larvae by different size groups of R. reticulata fishes was evaluated. In addition to this, the niche breadth (N) and diet breadth (B) were measured following Manly's selectivity index (Si) as an indicator of variation of such predation pattern in the presence of alternative prey types, like chironomid larvae and tubificid worms. RESULTS: The consumption of IV instar Cx. quinquefasciatus larvae by individual P. reticulata ranged between 65 and 84 in a 3 h feeding period and varied with the size of fish (F2,33 = 34.91; p < 0.001). The selectivity coefficient revealed a significantly low preference for the Cx. quinquefasciatus larvae (0.16, CL: 0.05-0.27; p < 0.05) compared to the chironomid larvae and tubificid worms, when all the three prey types were present. The niche breadth (N) and diet breadth (B) ranged from 0.77 to 0.92 and 0.69 to 0.93, respectively. The total consumption of all the prey types varied with the predator density, but the selectivity index for the mosquito larvae was significantly low in all the instances. INTERPRETATION & CONCLUSION: P. reticulata can consume a good number of mosquito larvae, with the consumption rate varying with the body size. P. reticulata fishes exhibit low preference for mosquito larvae as prey in the presence of alternative controphic preys like chironomid larvae and tubificid worms. Though establishment and sustenance of P. reticulata in new habitats will be favoured by the presence of alternative preys, but vulnerability of mosquito larvae may be reduced with availability of multiple preys in natural conditions.

Studies on mosquitoes breeding in rock pools on inselbergs around Zaria, northern Nigeria.

BACKGROUND & OBJECTIVES: Rainwater often collects in depressions on rocks to form pools that are ideal breeding sites of mosquito vectors of diseases. Knowledge on the existence of disease vectors in these remote and relatively inaccessible locations could improve epidemiologic understanding and control capabilities. This study identifies mosquito species, their relative abundance and physicochemical characteristics of breeding microhabitats in rock pools on four inselbergs in northern Nigeria. METHODS: Soup ladle dipper was used to obtain representative samples of larval mosquitoes breeding in 141 rock pools on four inselbergs. Physicochemical parameters (depth, electrical conductivity, pH, surface area, temperature and total dissolved solids) of the pools were determined. Larvae were preserved in 70% alcohol and identified microscopically to species using taxonomic keys. Statistical correlation analysis and ANOVA were used to test the associations between physicochemical parameters and mosquito abundance, and for differences amongst inselbergs. RESULTS: Of 2991 larvae, five species of mosquito distributed in three genera (Anopheles, Aedes and Culex) including Ae. vittatus (92.88%), An. ardensis (0.13%), An. distinctus (1.67%), An. wilsoni (0.13%) and Cx. ingrami (5.18%) bred in the rock pools, Up to five species occurred per pool in various conspecific and heterogeneric combinations. Except for Ae. vittatus, the physicochemical parameters of the pools correlate significantly with species abundance. CONCLUSION: Ae. vittatus, a potential vector of yellow fever in Nigeria breeds profusely in rock pools on inselbergs around Zaria. For comprehensive vector implication and control, rock pools should be amongst the habitats of focus in yellow fever epidemiology.

Evaluación del nicho ecológico deformas larvales de Aedes aegypti y Culex quinquefasciatus (Díptera: Culicidae) en una comunidad urbana de San José, Costa Rica / Evaluation of the ecological niche of Aedes aegpti and Culex quinquefasciatus (Díptera: Culicidae) larvae in an urban community of San José, Costa Rica

Observations related to the width and overlap of the ecological niche for larval forms of Aedes aegypti and Culex quinquefasciatus in artificial containers were performed using the data obtained during two laval surveys in the four sectors of the neighborhood 'La Carpio', San Jose, Costa Rica. 'La Carpio' was the first community of the Metropolitan Area of San José that suffered a dengue outbreak. The first survey was performed in the dry season of 2003 and the second one in the wet season of the same year. The width of niche was expressed using the Levin Index, and the overlap of niche was determined by the Morisita Index modified by Horn. In both larval surveys Ae. aegypti and Cx. quinquefasciatus were present. Ae. aegypti showed higher values for width of niche in the four sectors of the neighborhood and during both surveys.During the first larval survey (dry season of 2003), there was an overlap of niche only in sectors I and 3. In the wet season, the overlap was observed in the four sectors, but the values were higher in sectors I and 2. Results show that Ae. aegypti is the most common species of mosquitoes in artificial containers in the neighborhood, and that the role of Cx. quinquefasciatus as modulator of the Ae. aegypti populations could be limited.

Se realizaron observaciones relativas a la amplitud y solapamiento del nicho ecológico para las formas larvales de Aedes aegypti y Culex quinquefasciatus en contenedores artificiales, utilizando datos obtenidos in dos encuestas larvales que se ejecutaron en los cuatro sectores que conforman el poblado 'La Carpió', San José, Costa Rica. 'La Carpió' fue la primer comunidad del Área Metropolitana de San José en sufrir un brote de dengue. La primera encuesta tuvo lugar en la estación seca del 2003 y la segunda se realizó en la estación lluviosa del mismo a +/- o. La amplitud de nicho fue expresada por medio del índice de Levin y el solapamiento de nicho fue calculado mediante el índice de Morisita modificado por Horn. En ambas encuestas Ae. aegypti y Cx. quinquefasciatus estuvieron presentes. Ae. aegypti mostró los valores más elevados en lo referente a amplitud de nicho en los cuatro sectores de la comunidad durante ambas estaciones. En la primer encuesta larval (estación seca del 2003), hubo solapamiento de nicho sólo en los sectores 1 y 3. En la estacón lluviosa el solapamiento fue observado en los cuatro sectores, pero los valores más elevados se dieron en los sectores 1 y 2. Los resultados muestran que Ae. aegypti es el mosquito más abundante en contenedores artificiales en la comunidad y el papel de Cx. quinquefasciatus como modulador de las poblaciones parece ser limitado.

Predatory efficiency of the sewage drain inhabiting larvae of Toxorhynchites splendens Wiedemann on Culex quinquefasciatus Say and Armigeres subalbatus (Coquillett) larvae.

The rate of predation by stage IV instar Toxorhynchites splendens larvae on the equivalent instar stage larvae of Culex quinquefasciatus and Armigeres subalbatus, co-occurring in sewage drains, were noted for a period of three consecutive days in the laboratory using different prey densities and combinations. The rate of predation varied by age of the predator, density of prey, and prey type. The number of Ar. subalbatus larvae consumed by a single Tx. splendens larva ranged between 0.50 +/- 0.71 and 16.40 +/- 2.01; while for Cx. quinquefasciatus larvae, the number consumed ranged from 0.20 +/- 0.42 to 20.40 +/- 1.43 per day. The pupation rates of the prey species varied in respect to control, with a minimum of 0.20 +/- 0.42 pupa/day to a maximum of 12.20 +/- 2.30 pupa/day in the presence of Tx. splendens. The values for the controls were 1.00 +/- 0.87 and 14.44 +/- 2.83 pupa/day, respectively. Irrespective of prey densities and combinations, a single Tx. splendens fourth instar larvae was found to consume on average 10.07 larvae on the first day 16.57 larvae on the second day and 4.38 larvae on the third day, killing a total of 17.70 to 45.10 larvae, in three days. In the presence of Tx. splendens, the cumulative pupation, irrespective of prey, remained between 12.20 and 45.10, and differed significantly from control where the values were between 13.90 and 54.70. The results indicate that Tx. splendens can significantly reduce immature numbers and lower the rate of pupation of Cx. quinquefasciatus and Ar. subalbatus. Tx. splendens may be a potential biological resource in the control of mosquitoes inhabiting sewage drains.

Laboratory and field evaluation of an oviposition trap for Culex quinquefasciatus(Diptera: Culicidae)

An ovitrap (BR-OVT) based on physical and chemical stimuli for attracting gravid Culex quinquefasciatus (Diptera: Culicidae) females was developed and evaluated under laboratory and field conditions. Attractants were assayed using alternative chamber bioassays prior to being used in the BR-OVT oviposition trap. A significant preference of gravid females for sites containing conspecific egg rafts was observed, as a response to the natural oviposition pheromone, as well as for sites treated with the synthetic pheromone erythro-6-acetoxy-5-hexadecanolide. Five- to 20-day old grass infusion was strongly attractive to gravid females for laying eggs. On the other hand, entomopathogenic Bacillus sphaericus (Bs) did not influence the choice of an oviposition site when used in combination with grass infusion and can therefore be used as a larvicide in ovitraps. Results from field trials showed that the BR-OVT with grass infusion and with or without Bs works as a preferred oviposition site for Cx. quinquefasciatus. The BR-OVT was more effective for egg collection when placed indoors and comparison with the number of egg rafts laid in cesspits over 40 days indicates that this very simple ovitrap may be a useful tool for monitoring populations of the most important of the vectors of bancroftian filariasis.

New record and larval habitats of Culex eduardoi (Diptera: Culicidae) in an irrigated area of Patagonia, Chubut Province, Argentina

The object of the present work was to identify the larval habitats of Culex eduardoi and to determine the microenvironmental conditions related to their presence in different artificial freshwater environments (temporary, semi-permanent, irrigation ditches, and drainage ditches) in tillable areas of Chubut Province, Argentina. This report represents the first record of Cx. eduardoi from this Province and extends its range to latitude 45°S. Immature stages of Cx. eduardoi were found in 8 out of 109 (7.3 percent) freshwater habitats and were significantly more prevalent in semi-permanent water bodies. Positive sites had significantly larger surface areas and more vegetation cover than negative sites.

Behavioural biting preference of Culex quinquefasciatus in human host in Lagos metropolis Nigeria.

BACKGROUND & OBJECTIVES: Olfactory cues play an important role in the attraction of major disease vectors towards their host. Hence we intend to investigate the contribution of selected parts of the human host on the behavioural biting preference of Culex quinquefasciatus. METHODS: Two volunteers were trained to collect host seeking female mosquitoes landing to feed on different parts of the lower limbs. The Cx. quinquefasciatus were collected in paper cups with the aid of a flash-light and aspirator. Each paper cup was labeled to represent the selected parts where the mosquitoes were collected. RESULTS: The composition of Cx. quinquefasciatus from the total mosquitoes collected showed that Cx. quinquefasciatus was more predominant (90%) over other species present. The average minimum and maximum atmospheric temperature recorded during the night catches were 27 and 29.5 degrees C while the average relative humidity range was 78-81.6%. The behavioural biting preference results obtained showed that the density of Cx. quinquefasciatus mosquitoes preferring the foot region (298) was significantly higher (p > 0.05) when compared with other different parts of the human host such as the ankle, calf and the thigh. INTERPRETATION & CONCLUSION: The study indicates that the foot region of the human host has a stronger influence in orientating mosquitoes towards the human host. Hence, the exploitation of the characteristic human odour will add to the existing vector control strategies.