Does habitat modification affect oviposition by the salt marsh mosquito, Ochlerotatus vigilax (Skuse) (Diptera : Culicidae)?

Studies were conducted at sites in south-cast Queensland, Australia, to investigate the effect of habitat modification for mosquito control on the distribution of eggshells of the salt marsh mosquito, Ochlerotatus vigilax (Skuse). Modifications were mainly tunnelling, but an Open Marsh Water Management (OMWM) site and a grid-ditched site were also included. There were two separate experimental designs: one was data collected Before and After (BA) modification and the other was for other sites with a Treatment and Control (TC) experimental design. For the BA data, there were significant reductions in eggshells after modification. Eggshells were generally fewer after modification in areas which were close to unrestricted tidal flushing. A sandy substrate and vegetation changes which resulted in reduced Sporobolus virginicus or mixed Sporobolus and Sarcocornia quinqueflora also contributed to the effect. In the TC experiment, there was no effect of modification at the tunnelled site, eggshells were fewer at the OMWM site, but there were more eggshells at the grid-ditched site. There was some general indication that recent oviposition activity was reduced in sites that had been modified, evidenced by a relatively small proportion of young (dark coloured) eggshells.

Evaluation of liquid Bacillus thuringiensis var. israelensis products for control of Australian Aedes arbovirus vectors

Laboratory bioassay studies were conducted in southeast Queensland, Australia,: on the efficacy of Teknar (R), VectoBac (R) 12AS, and Cybate (R) (active ingredient: 1,200 international toxic units Bacillus thuringiensis var, israelensis [Bti]) against 3rd instars of the arbovirus vectors Aedes aegypti. Ae. notoscriptus, Ae. vigilax, and Ae. camptorhynchus. Probit analyses were then used to determine LD,, (median lethal dose), LD95, and lethal dose ratios (LDR). Aedes aegypti and Ae. notoscriptus, both container-habitat species, tolerated the highest Bti concentrations compared with saltmarsh Ae. vigilax and Ae. camptorhynchus. For example, the LDR for Ae. vigilax versus Ae. notoscriptus exposed to Cybate was 0.14 (95% confidence limit [CL] 0.03-0.61). Similarly, the Cybate LDR for Ae. camptorhynchus versus Ae. notoscriptus was 0.22 (95% CL 0.07-0.70). Teknar produced similar results with an LDR of 0.21 (95% CL 0.04-1.10) for Aedes vigilax versus Aedes notoscriptus. Differences in product efficacy were found when tested against the 2 container-breeding species. Cybate was less effective than Teknar with LDRs of 1.55 (95% CL 0.65-3.67) and 1.87 (95% CL 0.68-5.15) for Aedes aegypti and Ae. notoscriptus, respectively. The significant differences in susceptibility between mosquito species and varying efficacy between products highlight the importance of evaluating concentration-response data prior to contracting with distributors of mosquito control products. This information is crucial to resistance management strategies.

Enhancement or modulation of the vector competence of ochlerotatus vigilax (Diptera : Culicidae) for Ross River virus by temperature

Two different doses of Ross River virus (1111) were fed to Ochlerotatus vigilax (Skuse), the primary coastal vector in Australia; and blood engorged females were held at different temperatures up to 35 d. After ingesting 10(4.3) CCID50/Mosquito, mosquitoes reared at 18 and 25degreesC (and held at the same temperature) had higher body remnant and head and salivary gland titers than those held at 32degreesC, although infection rates were comparable. At 18, 25, and 32degreesC, respectively, virus was first detected in the salivary glands on days 3, 2, and 3. Based on a previously demonstrated 98.7% concordance between salivary gland infection and transmission, the extrinsic incubation periods were estimated as 5, 4, and 3 d, respectively, for these three temperatures. When Oc. vigilax reared at 18, 25, or 32degreesC were fed a lower dosage of 10(3.3) CCID50 RR/mosquito, and assayed after 7 d extrinsic incubation at these (or combinations of these) temperatures, infection rates and titers were similar. However, by 14 d, infection rates and titers of those reared and held at 18 and 32degreesC were significantly higher and lower, respectively. However, this process was reversible when the moderate 25degreesC was involved, and intermediate infection rates and titers resulted. These data indicate that for the strains of RR and Oc. vigilax used, rearing temperature is unimportant to vector competence in the field, and that ambient temperature variations will modulate or enhance detectable infection rates only after 7 d: extrinsic incubation. Because of the short duration of extrinsic incubation, however, this will do little to influence RR epidemiology, because by this time some Oc. vigilax could be seeking their third blood meal, the latter two being infectious.

Ross River virus transmission, infection, and disease: a cross-disciplinary review

Ross River virus (RRV) is a fascinating, important arbovirus that is endemic and enzootic in Australia and Papua New Guinea and was epidemic in the South Pacific in 1979 and 1980. Infection with RRV may cause disease in humans, typically presenting as peripheral polyarthralgia or arthritis, sometimes with fever and rash. RRV disease notificatïons in Australia average 5,000 per year. The first well-described outbreak occurred in 1928. During World War II there were more outbreaks, and the name epidemic polyarthritis was applied. During a 1956 outbreak, epidemic polyarthritis was linked serologically to a group A arbovirus (Alphavirus). The virus was subsequently isolated from Aedes vigilax mosquitoes in 1963 and then from epidemic polyarthritis patients. We review the literature on the evolutionary biology of RRV, immune response to infection, pathogenesis, serologic diagnosis, disease manifestations, the extraordinary variety of vertebrate hosts, mosquito vectors, and transmission cycles, antibody prevalence, epidemiology of asymptomatic and symptomatic human infection, infection risks, and public health impact. RRV arthritis is due to joint infection, and treatment is currently based on empirical anti-inflammatory regimens. Further research on pathogenesis may improve understanding of the natural history of this disease and lead to new treatment strategies. The burden of morbidity is considerable, and the virus could spread to other countries. To justify and design preventive programs, we need accurate data on economic costs and better understanding of transmission and behavioral and environmental risks.

Mosquito isolates of Ross River virus from Cairns, Queensland, Australia

During 1996-1998 60,619 mosquitoes were collected around Cairns, Australia and processed for Alphavirus isolation. Thirty-three isolates of Ross River (RR) virus were made from 9 species, Aedes imprimens, Aedes kochi, Aedes notoscriptus, Aedes vigilax, Culex annulirostris, Culex gelidus, Mansonia septempunctata, Verrallina (formerly Aedes) carmenti, and Verrallina lineatus. Attempts to isolate RR virus from 121 Aedes aegypti were unsuccessful. Twenty six (79%) of the isolates came from within 1 km of a colony of spectacled flying-foxes, Pteropus conspicillatus. The minimum infection rate for these mosquitoes was 1.0 compared with 0.2 per 1,000 for mosquitoes trapped at all other sites. Ross River virus has not previously been isolated from Ae. imprimens, Cx. gelidus, Ma. septempunctata, Ve. carmenti, or Ve. lineatus. This is also the first isolation of an arbovirus from Cx. gelidus in Australia. In conclusion, the vector status of Ve. carmenti, Ae. aegypti and Mn. septempunctata warrants further study. This study also provides evidence that P. conspicillatus may be a reservoir host.

Experimental infection of Australian brushtail possums, Trichosurus vulpecula (Phalangeridae : Marsupialia), with Ross River and Barmah Forest viruses by use of a natural mosquito vector system

Brushtail possums, Trichosurus vulpecula Kerr, were experimentally infected with Ross River (RR) or Barmah Forest (BF) virus by Aedes vigilax (Skuse) mosquitoes. Eight of 10 animals exposed to RR virus developed neutralizing antibody, and 3 possums developed high viremia for < 48 hr after infection, sufficient to infect recipient mosquitoes. Two of 10 animals exposed to BF virus developed neutralizing antibody. Both infected possums maintained detectable neutralizing antibody to BF for at least 45 days after infection (log neutralization index > 2.0 at 45 days). Eight possums did not develop neutralizing antibody to BF despite exposure to infected mosquitoes. These results suggest that T. vulpecula may potentially act as a reservoir species for RR in urban areas. However, T. vulpecula infected with BF do not develop viremia sufficient to infect mosquitoes and are unlikely to be important hosts for BF.

Spatial distribution of vectors of Ross River virus and Barmah Forest virus on Russell Island, Moreton Bay, Queensland

We used a network of 20 carbon dioxide- and octenol-supplemented light traps to sample adult mosquitoes throughout Russell Island in southern Moreton Bay, south-east Queensland. Between February and April 2001, an estimated 1365 564 adult female mosquitoes were collected. In contrast to an average catch of 9754 female mosquitoes per trap night on Russell Island, reference traps set on Macleay Island and on the mainland returned average catches of 3172 and 222, respectively. On Russell Island, Ochlerotatus vigilax (Skuse), Coquillettidia linealis (Skuse), Culex annulirostris Skuse and Verrallina funerea (Theobald), known or suspected vectors of Ross River (RR) and/or Barmah Forest (BF) viruses, comprised 89.6% of the 25 taxa collected. When the spatial distributions of the above species were mapped and analysed using local spatial statistics, all were found to be present in highest numbers towards the southern end of the island during most of the 7 weeks. This indicated the presence of more suitable adult harbourage sites and/or suboptimal larval control efficacy. As immature stages and the breeding habitat of Cq. linealis are as yet undescribed, this species in particular presents a considerable impediment to proposed development scenarios. The method presented here of mapping the numbers of mosquitoes throughout a local government area allows specific areas that have high vector numbers to be defined.

Ross River virus disease clusters and spatial relationship with mosquito biting exposure in Redland Shire, southern Queensland, Australia

The spatial heterogeneity in the risk of Ross River virus (family Togaviridae, genus Alphavirus, RRV) disease, the most common mosquito-borne disease in Australia, was examined in Redland Shire in southern Queensland, Australia. Disease cases, complaints from residents of intense mosquito biting exposure, and human population data were mapped using a geographic information system. Surface maps of RRV disease age-sex standardized morbidity ratios and mosquito biting complaint morbidity ratios were created. To determine whether there was significant spatial variation in disease and complaint patterns, a spatial scan analysis method was used to test whether the number of cases and complaints was distributed according to underlying population at risk. Several noncontiguous areas in proximity to productive saline water habitats of Aedes vigilax (Skuse), a recognized vector of RRV, had higher than expected numbers of RRV disease cases and complaints. Disease rates in human populations in areas which had high numbers of adult Ae. vigilax in carbon dioxide- and octenol-baited light traps were up to 2.9 times those in areas that rarely had high numbers of mosquitoes. It was estimated that targeted control of adult Ae. vigilax in these high-risk areas could potentially reduce the RRV disease incidence by an average of 13.6%. Spatial correlation was found between RRV disease risk and complaints from residents of mosquito biting. Based on historical patterns of RRV transmission throughout Redland Shire and estimated future human population growth in areas with higher than average RRV disease incidence, it was estimated that RRV incidence rates will increase by 8% between 2001 and 2021. The use of arbitrary administrative areas that ranged in size from 4.6 to 318.3 km2, has the potential to mask any small scale heterogeneity in disease patterns. With the availability of georeferenced data sets and high-resolution imagery, it is becoming more feasible to undertake spatial analyses at relatively small scales.

Dimorfismo sexual alar em Aedes scapularis (Diptera: Culicidae)

A detecção do sexo de mosquitos da família Culicidae é importante em estudos faunísticos e epidemiológicos, pois somente as fêmeas possuem competência vetora para patógenos. O dimorfismo sexual de genitália e de apêndices cefálicos é, em geral, facilmente visível em culicídeos. As asas também podem ser dimórficas e assim poderiam complementar o procedimento de sexagem. No entanto, tal distinção não é facilmente notável à observação direta. Visando descrever formalmente o dimorfismo sexual alar em Aedes scapularis, um culicídeo vetorialmente competente para arbovírus e filárias, asas de machos e fêmeas foram comparadas usando-se métodos de morfometria geométrica e análise estatística multivariada. Nestas análises, populações dos municípios São Paulo e Pariquera-Açu (Estado de São Paulo) foram amostradas. A forma das asas mostrou evidente dimorfismo sexual, o que permitiu um índice de acurácia de 100% em testes-cegos de reclassificação, independentemente da origem geográfica. Já o tamanho alar foi sexualmente dimórfico apenas na população de São Paulo. Aparentemente, a forma alar é evolutivamente mais estável que o tamanho, interpretação que está de acordo com a teoria de Dujardin (2008b), de que a forma alar de insetos seria composta por caracteres genéticos quantitativos e pouco influenciada por fatores não-genéticos, enquanto que o tamanho alar seria predominantemente determinado por plasticidade decorrente de influências ambientais.

Competição entre larvas de Aedes aegypti e Aedes albopictus em laboratório

Este estudo teve como objetivo avaliar os efeitos da competição larval intra e interespecífica entre Aedes aegypti e Aedes albopictus, sobre sobrevivência de larvas, tempo de desenvolvimento e comprimento de asa. O experimento foi realizado em três densidades com 5 proporções das espécies. A sobrevivência de Aedes aegypti apresentou-se superior a de Aedes albopictus em densidade intermediária e inferior em densidade alta. Somente Aedes albopictus teve seu tempo de desenvolvimento afetado. Diferenças encontradas nas comparações das combinações das espécies demonstraram que o comprimento médio de asas de Aedes aegypti, no geral, foi maior que Aedes albopictus. Nas duas espécies, a competição afetou mais o comprimento de asa e a sobrevivência que o tempo de desenvolvimento. Aedes aegypti parece apresentar maior capacidade competitiva em relação a Aedes albopictus em densidade intermediária.

Evaluation of oviposition traps as an entomological surveillance method for Aedes aegypti (Diptera, Culicidae)

This study aimed to describe the behavior of oviposition traps for Aedes aegypti over time, to compare it with the larval survey and to investigate the association with climatic variables. It was conducted in São José do Rio Preto city, São Paulo. Daily climatic data and fortnightly measurements for oviposition traps and larval infestation were collected from October 2003 to September 2004. Three different periods were identified in the behavior of oviposition traps' positivity and mean number of eggs: increase, plateau and decrease in values. These measurements followed the variation of climatic data from the first and third periods. High correlation was obtained between the positivity and the mean number of eggs. The oviposition traps showed higher capacity to detect the vector than did larval survey. It was observed that the first (October to December) and third (May to September) periods were considered to be the most suitable to use oviposition traps than larval surveys.

Estimação da infestação predial por Aedes aegypti (Díptera: Culicidae) por meio da armadilha Adultrap

Foi utilizada a armadilha Adultrap em uma amostra de domicílio preconizada pelo levantamento de índice rápido de infestação por Aedes aegypti (LIRAa) para mensuração do número de adulto de Aedes aegypti no domicílio. Foi vistoriada uma média de 555 imóveis mês: 15 unidades continham criadouros da espécie; e 53, a presença de fêmeas. O índice de infestação para larva/pupa (IPL) variou de zero ao máximo de 4,9 por cento, enquanto o índice de infestação para adulto (IPA), de 2,21 a 17,32 por cento. O teste de MacNemar mostrou diferenças significativas entre a positividade de IPL e IPA em todos os meses do ano. Além disso, detectaram-se fêmeas de Ae. Aegypti em período de baixa densidade populacional, sem o caráter invasivo e incômodo da pesquisa de recipientes para o IPL. A Adultrap mostrou-se útil para revelar situações propícias à transmissão da dengue, bem como de fácil operacionalidade

Proteção de Bromeliaceae para evitar a formação de criadouros de Aedes aegypti (Diptera: Culicidae)

As plantas da família bromeliaceae constituem criadouros de Aede aegypti. O presente estudo de campo mostrou que medidas mecânicas podem ser uma solução para o controle do mosquito nessas plantas. Na região norte do estado do Paraná, área de infestação por Ae. aegypti, q5 bromélias foram monitoradas durante um ano após receberem tratamento com palha de madeira e cascas de árvore. Nesse período não foram observadas formas imaturas de mosquitos, o que sugere que o uso deste material natural pode servir como medida complementar aos programas de controle vetorial.

Registro de Aedes albopictus em áreas epizoóticas de febre amarela das Regiões Sudeste e Sul do Brasil (Díptera:Culicidae)

Durante estudo biológico e ecológico sobre mosquitos levado a cabo em área com registro de epidemia de febre amarela silvestre e epizootia em macacos, foram encontrados adultos de Aedes Albopictus. A tendência da espécie para invadir ambiente extradomiciliar potencializa a chance de infecção natural, ao tempo em que evolui para formar um elo entre focos naturais de vírus e o ambiente urbano. Esta Nota Técnica representa um alerta aos gestores dos três poderes públicos sobre perspectivas de mudanças no perfil epidemiológico atual da febre amarela no Brasil