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PubMed1982

Melanization and encapsulation in Aedes aegypti and Aedes togoi in response to parasitization by a filarioid nematode (Breinlia booliati).

In Aedes aegypti (Singapore strain), s refractory host, there was a marked progressive decline of developing larvae of Breinlia booliati during the incubation period. However, in Aedes togoi, a susceptible host, the filarial larvae developed normally and the number of larvae remained constant throughout the incubation period. Encapsulation and melanization of B. booliati larvae in Ae. aegypti and Ae. togoi were studied. Ae. togoi occasionally mounted a defence reaction to the infection. In Ae. aegypti, various stages of filarial larvae were frequently affected by the defence mechanisms of the host, and a relatively large number of melanized larvae were recovered in dissections throughout the incubation period. The process of melanization is described and the relationship between melanization and haemocytes of mosquitoes is discussed. Haemocytes of the mosquito host appeared to be involved in the encapsulation of filarial larvae, as evidenced by adherence of cells to the cuticle of the larvae and the formation of a translucent, gelatinous envelope which contained intact cells, necrotic cells, spaces and numerous whitish granules. The possible involvement of a humoral reaction in bringing about the degeneration and retardation of the filarial larvae is discussed.

Aedes↗
PubMed1999

Immunity proteins from mosquito cell lines include three defensin A isoforms from Aedes aegypti and a defensin D from Aedes albopictus.

An Aedes aegypti mosquito cell line, Aag-2, exhibits a response to immune stimulation that is qualitatively similar to that of C7-10 cultured cells from the related mosquito, Aedes albopictus. Using SDS polyacrylamide gels, we found that a small peptide was preferentially induced by the treatment of growing cells with heat-killed, Gram-positive bacteria. By an analogy with other studies, this small peptide was postulated to be a member of the defensin family of insect immunity peptides. A differential display was used to obtain partial polymerase chain reaction products corresponding to mRNAs that were preferentially expressed in induced cells. One of these products, which contained the partial sequence of a defensin gene, was used to screen cDNA libraries from Ae. aegypti and Ae. albopictus cells. From Ae. aegypti cells, we found two previously described isoforms (A1 and A4) of mosquito defensin A, as well as a new isoform which we defined as A5. From Ae. albopictus cells, we found a new mature mosquito defensin, named D, which contains proline and isoleucine as the final amino acids. In both Ae. aegypti and Ae. albopictus cell lines, the expression of defensin mRNA was visible on Northern blots as early as 3 h after exposure to heat-killed bacteria, and defensin mRNA abundance was maximal at 12-36 h after induction.

Aedes↗
PubMed1992

Differential oviposition by Aedes hendersoni and Aedes triseriatus (Diptera: Culicidae) in response to chemical cues associated with treehole water.

The oviposition behavior of Aedes hendersoni Cockerell and Aedes triseriatus (Say) was examined in the laboratory by offering gravid females oviposition sites containing water from different treehole types and by varying the physical characteristics of oviposition sites. Ae. hendersoni females oviposited more frequently in containers with water from treeholes in which they are found commonly in nature (maple "deep rotholes") than in containers with water from holes in which they are found rarely (beech "pans"). In contrast, Ae. triseriatus eggs were distributed uniformly in containers holding the two types of treehole water. There were no differences between species in response to oviposition container height or orientation of the entrance hole (vertical or horizontal). Females of both species laid nearly all their eggs in containers with horizontal openings, and most were deposited at the higher of two levels. We suggest that the adaptive value of the oviposition behavior of Ae. hendersoni is to maximize fitness by reducing interspecific contact with Ae. triseriatus.

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PubMed1992

Susceptibility of selected strains of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) to chikungunya virus.

The relative susceptibility of selected strains of Aedes aegypti (L.) and Aedes albopictus (Skuse) fed on a viremic monkey to infection with chikungunya virus was determined. Infection rates were consistently higher in 10 strains of Ae. albopictus tested than in 7 strains of Ae. aegypti tested, regardless of the geographic location from which the strains originated or the dose of virus ingested. Similarly, virus dissemination rates were higher in the Ae. albopictus strains compared with the Ae. aegypti strains. For nearly all (11 of 12) strains tested of both species, groups of mosquitoes with one or more females with a disseminated infection transmitted virus by bite to weanling mice. Based on these studies, Ae. albopictus appears to be a more competent laboratory vector of chikungunya virus than does Ae. aegypti.

Aedes↗
PubMed1998

Laboratory and field evaluations of oviposition responses of Aedes albopictus and Aedes triseriatus (Diptera: Culicidae) to oak leaf infusions.

Organic infusions created by fermenting white oak (Quercus alba L.) leaves in water were evaluated as sources of attractant odorants and contact oviposition stimulants for gravid Aedes albopictus (Skuse) and Aedes triseriatus (Say). Infusions were bioassayed in the laboratory by giving single females a choice of ovipositing in 1 container with infusion and 7 containers with water. Ae. albopictus laid significantly more eggs in containers with infusion, regardless of concentration (dilutions ranging from 10 to 100%) or age (fermentation periods of 7, 28, 60 d), than in containers holding water. The largest proportion of eggs (76.8%) was deposited in response to a 60% concentration of 7-d-old infusion. In contrast, Ae. triseriatus exhibited variable oviposition responses but generally deposited the largest number of eggs in only a few concentrations of older age infusions. In binary "sticky screen" bioassays, there was no difference between the numbers of females attracted to infusion or water, indicating that oviposition responses to infusion were mediated by contact chemostimulants rather than by attraction to odorants. Oviposition responses to infusions by field populations of Ae. albopictus and Ae. triseriatus in Raleigh, NC, were evaluated with pairs of oviposition traps, one containing infusion and the other containing water. Generally, Ae. albopictus laid significantly more eggs in ovitraps containing infusion regardless of its age (7, 28, and 60 d old) or the mass of leaves fermented (126 g = 1x or 504 g = 4x) than in water. In contrast, Ae. triseriatus deposited an equivalent number of eggs in traps containing water or 1x, 80% infusion regardless of its age; however, the oviposition response to ovitraps containing 4x, 7-d-old, 50% infusion was significant. Placement of an automobile tire behind an ovitrap did not increase the number of Ae. albopictus eggs laid in ovitraps containing 4x, 7-d-old, 50% infusion or water relative to ovitraps without a tire. Our research indicates that baiting ovitraps with oak leaf infusion would increase the sensitivity of surveillance efforts for Ae. albopictus and Ae. triseriatus.

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PubMed1999

Vector competence of Aedes notoscriptus (Diptera: Culicidae) for Barmah Forest virus and of this species and Aedes aegypti (Diptera: Culicidae) for dengue 1-4 viruses in Queensland, Australia.

Aedes notoscriptus (Skuse) mosquitoes colonized from Brisbane, Queensland, Australia, were fed on blood suspensions containing either Barmah Forest (BF) virus, dengue virus type 1 (DEN-1), dengue virus type 2 (DEN-2), dengue virus type 3 (DEN-3), or dengue virus type 4 (DEN-4). Ae. notoscriptus was shown to be moderately susceptible to oral infection with BF virus, ID50 = 10(3.3) CCID50 per mosquito, with titers in infected mosquitoes peaking 10 d after infection. BF virus transmission occurred between days 5 and 12, with an average rate of 45% (range, 40-50%). For DEN 1-4, Ae. notoscriptus showed low level susceptibility to oral infection, with maximum head and thorax squash infection rates of 8, 5, 13, and 3%, respectively. Rates of infection were notably higher in a north Queensland strain of Aedes aegypti (L.) used as a positive control, with maximum thorax squash infection rates of 58, 68, 78, and 60% for DEN 1-4, respectively. On the basis of these data, it is concluded that Ae. notoscriptus could act as an efficient vector of BF in urban environments, but it is unlikely to be an important vector of DEN.

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PubMed2000

Invertebrate carcasses as a resource for competing Aedes albopictus and Aedes aegypti (Diptera: Culicidae).

Terrestrial invertebrate carcasses are an important resource for insects developing in pitcher plants. However, little is known of the role of these carcasses in other containers, which also receive leaf fall and stemflow inputs. This experiment investigated effects of accumulated invertebrate carcasses as a resource for two competing mosquitoes, Aedes albopictus (Skuse) and Aedes aegypti (L.), whether either species differentially benefited from accumulated carcasses, and if such a benefit affected interspecific competition. First, we measured accumulation of invertebrate carcasses in standard containers at a field site. We then used a replacement series with five different species ratios at the same total density, and varied the input of invertebrate carcasses [dead Drosophila melanogaster (Meigen) ] in three levels: none, the average input from our field site, or the maximum input recorded at our field site. Survivorship, development time, and mass were measured for each mosquito species as correlates of population growth, and were used to calculate a population performance index, lambda'. There were strong positive effects of invertebrate carcass additions on all growth correlates and lambda'. Differences in performance between species were pronounced in small or no carcass additions and absent in large inputs of invertebrate carcasses, but there was little evidence that inputs of invertebrate carcasses altered the competitive advantage in this system. These results suggest that terrestrial invertebrate carcasses may be an important resource for many types of container communities, and large accumulations of dead invertebrates may reduce resource competition between these mosquitoes, thus favoring coexistence. We propose that the total amount of resource, including accumulated invertebrate carcasses, may explain observed patterns of replacement involving these mosquitoes.

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PubMed2005

Comparative study on nocturnal behavior of Aedes aegypti and Aedes albopictus.

Nocturnal behavior of nonblood-fed females of Aedes aegypti (L.) and Aedes albopictus (Skuse) was studied using an automatic recording device equipped with a photoelectric sensor. Carbon dioxide, heating, and the contrast of the black and white colors were used as attractive cues for mosquitoes. The nocturnal host-seeking activity positively correlated with the increasing light intensity in both species. Ae. aegypti was found to be more sensitive to light than Ae. albopictus. The threshold of light intensity for the activation of the nocturnal host-seeking activity was <0.1 lx (approximately 0.01 foot candle) in Ae. aegypti and >10 lx (approximately 1 foot candle) in Ae. albopictus. Complete darkness during the daytime deactivated the host-seeking activity of both species, irrespective of their increasing flight activity controlled by their intrinsic circadian rhythms. This finding suggested that visual cues are indispensable for host-seeking behavior. The eye parameter value, the product of the ommatidial diameter, and the interommatidial angle were significantly larger in Ae. aegypti than those in Ae. albopictus, indicating that the eye of Ae. aegypti is more adapted to a darker environment.

Aedes↗
PubMed2005

Geographic distribution and breeding site preference of Aedes albopictus and Aedes aegypti (Diptera: culicidae) in Cameroon, Central Africa.

Presence in Cameroon of the recently introduced Aedes (Stegomyia) albopictus (Skuse) in association with the indigenous Aedes aegypti (L.) raises public heath concerns because it might alter the risk of arbovirus transmission. The breeding site and distribution of the two Stegomyia species are updated and reported following entomological surveys carried out in 22 localities throughout Cameroon, with a total of 1,353 containers with water visited. Ae. aegypti was found in every location sampled, showing higher infestation rates in northern Cameroon. Breeding populations of Ae. albopictus were observed in all 19 southern localities, up to the Adamaoua mountains, but the species was not recorded further north. In the area where both species are present, they were often sampled in the same larval developmental sites, suggesting convergent habitat segregation. The most frequently encountered artificial and natural breeding sites were used tires, discarded tins and plastic containers, abandoned car parts, brick holes, dead leaves on the ground, tree holes, and rock pools. Further monitoring of the demographic as well as geographic expansion of Ae. albopictus in this Afrotropical environment and its relationships with indigenous Ae. aegypti should provide insight into the biology of this highly invasive species and help to implement arboviruses surveillance programs in the area.

Aedes↗
PubMed2005

Blood feeding patterns of Aedes aegypti and Aedes albopictus in Thailand.

Aedes aegypti (L.) and Aedes albopictus (Skuse) were collected with aspirators from Mae Sot, Nakhon Sawan, Nakhon Ratchasima, Surat Thani, and Phatthalung study sites in Thailand from July 2003 though April 2004. The sandwich-B enzyme-linked immunosorbent assay was used to analyze 1,021 blood-fed specimens. Ae. aegypti almost exclusively fed on humans (99%, 658/664) in single host species, and 97% (86/88) of multiple-host bloodmeals included at least one human host. A low frequency of other hosts, including bovine, swine, cat, rat, and chicken were detected, but they represented <1% of bloodmeals. An even higher percentage of human feeding was detected in Ae. albopictus. Hosts of Ae. albopictus collected from sites in southern Thailand were entirely human (100%, n = 105) from both single and mixed meals. In the small number of double-host meals from Ae. albopictus, we detected 3.8% as swine-human and <1% from dog-human and cat-human. Forage ratios for Ae. aegypti indicated that human, dog, and swine were preferred hosts in order of preference. In contrast, bovine and chicken were avoided hosts for this species in Thailand.

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PubMed2005

Aedes aegypti (L.) and Aedes polynesiensis Marks (Diptera: Culicidae) in Moorea, French Polynesia: a study of adult population structures and pathogen (Wuchereria bancrofti and Dirofilaria immitis) infection rates to indicate regional and seasonal epidemiological risk for dengue and filariasis.

Populations of Aedes aegypti (L.) and Aedes polynesiensis (Marks) on Moorea Island, French Polynesia, the local vectors of dengue and filariasis, respectively, were sampled by landing/biting collection at nine localities on the east, north, and west coasts, during the late dry season, early and late wet season (September-May) 2003 and 2004, to investigate epidemiologically important features of the populations and compare them between regions and months. Biting rates of both species tended to increase (but not always significantly) for each species in each region each month from the late dry season to the late wet season, and the north coast region had significantly higher biting rates of Ae. aegypti. Insemination rates of Ae. polynesiensis females (94.5-98.8%) were consistently greater than those of Ae. aegypti (87.5-93.5%) throughout the study, but there was no significant difference in the insemination rates of either species between months and regions. Parity rates were generally highest in north coast samples and lowest in west coast samples for both species and generally increased (albeit not always significantly) by month for each species, with a range of 52.9-88.8% for Ae. polynesiensis and 28.6-53.6% for Ae. aegypti, although the high gravid rate (15.8-45.9%) of Ae. aegypti samples (reflecting its feeding more than once in a gonotrophic cycle) confounded both intraspecific and interspecific comparisons. Filarial infection was rare in Ae. aegypti, although both W. bancrofti and D. immitis were recorded, and infection rates in Ae. polynesiensis increased through the study period in each region for both filarias, with up to 4.6% infected and 1.4% infective for W. bancrofti and up to 6.3% infected and 2.5% infective for D. immitis. For W. bancrofti, infection rates were significantly lower on the west coast and also in the dry season, whereas rates for infective stages were significantly greater in the late wet season. For D. immitis there was no significant difference in infection rates between regions, but rates were significantly greater in the late wet season. Rainfall in all months sustains populations of both vectors and explains the relatively few significant differences between seasons; however, the wet season may provide for increased vector abundance and longevity, and present a potentially increased risk for transmission. Although the differences shown between regions also were limited in a statistical sense, there were increased risks for the northern and eastern regions, where both locals and tourists are concentrated and where the seaports and airport are located, and these areas should be priority targets for disease surveillance and vector control.

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PubMed1989

The vector competence of Culex annulirostris, Aedes sagax and Aedes alboannulatus for Murray Valley encephalitis virus at different temperatures.

Culex annulirostris Skuse, colonized from Brisbane, Queensland, and Mildura, Victoria, Australia, were effective vectors of Murray Valley encephalitis virus at 20, 27 and 32-35 degrees C with full extrinsic incubation periods of 15, 10 and 4 days respectively. At 20 degrees C, 7-11 days post-infection, transmission by the Mildura colony (0-20%) was less efficient than the Brisbane colony (30-70%) but both were capable of 75-100% transmission after longer extrinsic incubation periods. Discriminant analysis of body and salivary gland titres showed that these were not satisfactory indicators of transmission. Wild-caught Aedes sagax (Skuse) and Cx annulirostris from the Murray Valley showed equal competence, but Aedes alboannulatus (Macquart) was a poor vector. The results provide data on rural amplification of Murray Valley encephalitis virus during spring and suggest that further work on the potential of Ae. sagax as a natural vector is warranted.

Aedes↗
PubMed1991

Prospects for an invasion: competition between Aedes albopictus and native Aedes triseriatus.

Competition between larval populations of the native North American treehole mosquito Aedes triseriatus and Aedes albopictus, recently introduced from Asia to North America, was assessed by comparing per capita growth rate estimates for experimental cohorts of larvae developing under a variety of initial density combinations in fluid obtained from tires or from treeholes. Estimates of carrying capacities and competition coefficients indicate that competition between the two species will result in stable coexistence in treehole communities but local extinction of A. triseriatus in tire habitats.

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PubMed1987

Mechanical transmission of Bacillus anthracis by stable flies (Stomoxys calcitrans) and mosquitoes (Aedes aegypti and Aedes taeniorhynchus).

We evaluated the potential of stable flies, Stomoxys calcitrans, and two species of mosquitoes, Aedes aegypti and Aedes taeniorhynchus, to transmit Bacillus anthracis Vollum 1B mechanically. After probing on Hartley guinea pigs with a bacteremia of ca. 10(8.6) CFU of B. anthracis per ml of blood, individual or pools of two to four stable flies or mosquitoes were allowed to continue feeding on either uninfected guinea pigs or A/J mice. All three insect species transmitted lethal anthrax infections to both guinea pigs and mice. Both stable flies and mosquitoes transmitted anthrax, even when they were held at room temperature for 4 h after exposure to the bacteremic guinea pig before being allowed to continue feeding on the susceptible animals. This study confirms that blood-feeding insects can mechanically transmit anthrax and supports recent anecdotal reports of fly-bite-associated cutaneous human anthrax. The potential for flies to mechanically transmit anthrax suggests that fly control should be considered as part of a program for control of epizootic anthrax.

Aedes↗
PubMed1991

[Sampling study for larval density quantification of Aedes aegypti and Aedes albopictus in the state of São Paulo, Brazil].

The Yellow Fever and Dengue Vector Control Program developed by the Superintendency for the Control of Endemic Diseases in the State of S. Paulo recommends Aedes aegypti and Aedes albopictus larval density monitoring in cities with domiciliar infestation. The sampling plan which has been applied in the countries of the Presidente Prudente region (SP- Brazil) since 1987 is described. The infestation is measured by using the Breteau Index. A sample of buildings is drawn, monthly and independently, in the infested cities, in which measurements are to be made. The sample is stratified and the elementary unit selection is made by using two-stage cluster sampling: of blocks and buildings. The sample sizes were defined using the coefficient of variation and the intraclass correlation as estimated for towns covered by the Regional Health Service of S. José do Rio Preto. These sizes must be corrected periodically in accordance with the values of the Breteau Index and its variance obtained in previous months.

Aedes↗
PubMed2000

[Infestation of S. Paulo State, Brazil, by Aedes aegypti and Aedes albopictus].

OBJECTIVE: To study the influence of the distance between infested and non-infested areas in the geographical spread of Aedes aegypti and Aedes albopictuspopulations in the state of S. Paulo. Regional patterns were also studied, considering the determinants related to soil occupation. METHODS: Information related to the counties in the state of S. Paulo where were concentrations of Ae. aegypti and Ae. albopictus and counties infested up to the end of each year (1985 to 1995), both in the state of S. Paulo and in the neighboring states, were used. Four indicators were defined to analyze the infestation process. RESULTS/CONCLUSIONS: The analysis indicated the contribution of the states of Mato Grosso do Sul and Paraná for the initial Ae. aegypti infestation in the state of S. Paulo and Ae. albopictus infestation in the states of Rio de Janeiro and Minas Gerais. In the counties where there was a concentration of these species, their establishment was more frequent among those closer to the infested area. Seventy-five percent of the counties where there were established populations of Ae. aegypti and Ae. albopictus were situated up to 34 km and 60 km, respectively, from the nearest infested county. The analysis of the geographical spread rate of the Ae. aegypti revealed three different large areas with unexpected patterns: the area with greater demographic population density (east of the state) had the lower rate of geographical mosquito spread, indicating the existence of other factors with preponderant influence on the macro-regional patterns. For Ae. albopictus, there was no evidence of a relationship between their geographical spread patterns and the demographic population density.

Aedes↗
PubMed2002

[Climate and the superimposed distribution of Aedes aegypti and Aedes albopictus on infestation of São Paulo State, Brazil].

OBJECTIVE: To study the influence of climatic factors and superimposed distribution of Aedes aegypti and Aedes albopictus populations on their geographic dispersal in the state of São Paulo. METHODS: Data from government agencies on Ae. aegypti and Ae. albopictus foci and their distribution throughout counties of the state of São Paulo year by year, from 1985 to 1995, were obtained. Temperatures and rainfall data were also collected. Two indicators were used: infestation and rate. RESULTS AND CONCLUSIONS: The analysis indicated that the lower the temperature, the slower the geographic dispersal of Ae. aegypti population. This factor predominantly influenced the macro regional dispersal patterns of the species in the state of São Paulo. There was no clear influence of temperature on the dispersal of Ae. albopictus. The influence of rainfall on dispersal patterns was seen only for Ae. aegypti in a state area. No influence was detected on the prior presence of Ae. albopictus on the establishment of Ae. aegypti.

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