The energetic costs of diving in Aedes aegypti and Aedes albopictus pupae

Undisturbed mosquito pupae rest at the water surface and respond to passing shadows or vibrations by diving. Pupae do not feed and rely solely on energy stored from the larval stage. The ability of a newly emerged adult mosquito to survive, and therefore to transmit disease, depends on these energy reserves. Earlier studies of diving behavior in Aedes aegypti, Ae. albopictus, and Ae. triseriatus pupae provided evidence that pupae sense their state of buoyancy and modify their diving behavior accordingly. With strong stimulation pupae tend to dive to a depth where they become neutrally or negatively buoyant and commonly rest on the bottom. This behavior, as well as the tendency to rest when not disturbed, may logically be viewed as energy-conserving. The results of these studies also generated the hypothesis that the diving behavior displayed by these container-breeding mosquitoes helps them avoid being washed from their container by overflowing water during rainfall. Rainfall stimulates diving and logically, prolonged, heavy rainfall stimulates excessive diving, a likely drain on energy reserves. Our objectives were to determine, in Ae. aegypti and Ae. albopictus, the energetic costs associated with resting behavior, with frequent diving, and with buoyancy reduction. Using survival rate, mean survival after adult emergence, and measurement of total calories, we found a clear energetic cost associated with frequent diving. In contrast, relative to diving, essentially no energy cost was associated with buoyancy reduction, that is, pupae behave in response to variations in buoyancy in a way that does not impact significantly on energy reserves.     

Frequency and spatial distribution of Aedes aegypti and Aedes albopictus (Diptera, Culicidae) in Rio de Janeiro, Brazil

We evaluated the intra- and peri-domiciliary distribution of Aedes aegypti and Ae. albopictus in urban, suburban, and rural districts in the municipalities of Nova Igua?u and Rio de Janeiro, Brazil, from August 2002 to July 2004. Mostly Ae. aegypti females and males were captured in urban areas (56%) and indoors (78%), suggesting a preference by this species to rest inside houses and in areas with high human density, a behavior that favors vector-human contact. Meanwhile, Ae. albopictus females and males were much more common in rural areas (93%) and outdoors (90%), demonstrating their preference to rest in areas with more vegetation, reducing both the probability of vector-human contact and thus their potential role in dengue transmission in the area.     

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.     

Dominance of Aedes aegypti over Aedes albopictus in the southeastern coast of Brazil

OBJECTIVE: To assess infestation of Aedes aegypti and Aedes albopiticus and describe their association with weather conditions and container colonization in urban areas. METHODS: The town of S?o Sebasti?o in the southeastern coast of Brazil was selected. It was used data from the Dengue and Yellow Fever Vector Control Program of the State of S o Paulo, Brazil, that encompasses entomological surveillance at strategic positions, traps and foci demarcation. Strategic positions sites are fixed sites with containers in adequate conditions for larvae growth. Statistical analysis was performed using Kruskal-Wallis test, Dwass-Steel-Chritchlow-Fligne test and Mann-Whitney test. RESULTS: There was found an annual growth of positive traps and strategic positions of Ae. aegypti and a drop in Ae. albopictus population. An increase in immature Ae. aegypti and a drop of the other species were also seen. A gradual increase of positive dwellings for Ae. aegypti was noticed outgrowing Ae. albopictus population. There was a weak correlation of the Aedes species with abiotic factors. Higher numbers of immature mosquitoes of both species were found in artificial containers which could be eliminated. CONCLUSIONS: The study showed Ae. aegypti was predominant in urban areas, indicating that its growth seems to have affected the coexistence with other species. Natural selection could be in place contributing to Aedes aegypti and albopictus species separation.     

Biology and distribution of Aedes albopictus and Aedes aegypti in Madagascar

The biology and distribution of the 2 Malagasy Stegomyia species, Aedes aegypti and Aedes albopictus, is updated and reported. Aedes aegypti is present in the western and southern regions and Ae. albopictus in the east and on the high plateau. Some unusual locations are noted. The ranges of Ae. albopictus and Ae. aegypti on Madagascar overlap only slightly. Aedes aegypti is present in the west and in the south, while the Ae. albopictus distribution area is in the east and on the central high plateau. Climatic factors (number of dry months, annual rainfall and temperature), rather than competitive interactions, appear to be the major determinants of the distribution of these species. Aedes aegypti is just slightly anthropophilic, contrary to Ae. albopictus. Babanki virus and MMP 158 virus were isolated from Ae. aegypti; no virus has been isolated from Ae. albopictus.     

Replacement of Aedes aegypti by Aedes albopictus in Mobile, Alabama.

Aedes albopictus was first detected in Mobile, AL, in 1987 during a CDC sponsored ovitrap survey in the Historic District. A comparison of ovitrap and larval surveys, done in 1957, 1984, 1987 and 1990, indicates that Ae. albopictus had replaced Aedes aegypti in urban Mobile. Possible explanations of this replacement, including displacement, are discussed.     

Experimental infection of Aedes aegypti and Aedes albopictus with dengue viruses

The susceptibility of two Aedes (Stegomyia) species, Ae. aegypti and Ae. albopictus, to infection with dengue virus was assessed using both natural feeding on a viraemic gibbon and a membrane feeding technique. Both species were highly susceptible to dengue virus infection.     

Susceptibility of Aedes aegypti larvae to the insecticide temephos in the Federal District, Brazil

OBJECTIVE: To study the susceptibility status of Aedes aegypti to the organophosphate insecticide temephos. METHODS: Samples of Ae. aegypti larvae were obtained, using ovitraps, from eight cities of the Federal District, central Brazil, in 2000 and 2001. Larvae were submitted to the diagnostic dose of 0.012 mg/l temephos, as recommended by standard World Health Organization methodology. Field populations were tested in parallel with reference strains Rockefeller and DIVAL, from the Environmental Surveillance Directory (DIVAL) insectary. The concentration and purity of temephos solutions were verified by gas chromatography. Correlation calculations were performed using StatView - SAS Institute Inc., version 5. Student's t test was used for detecting differences in susceptibility, with significance levels of alpha=0.05. RESULTS: In 2000, Ae. aegypti larvae populations from Taguatinga, Guara, and Nucleo Bandeirante showed resistance to temephos, with mortality ranging from 54.1 to 63.4%. The populations from Gama, Planaltina, and Sobradinho showed altered levels of susceptibility (mortality ranging from 83.6 to 92.8%). The population from Ceilandia was the only susceptible one, with 98% mortality. In 2001, all populations tested were resistant (44.4 to 66.4% mortality). No significant correlation was found between the susceptibility of populations and the distance between the cities of origin, or the amount of insecticide applied in the years preceding the study. CONCLUSIONS: Ae. aegypti susceptibility to temephos is changing in the Federal District. It is essential to continue monitoring the resistance of this vector to insecticides in order to ensure the efficiency of programs aimed at vector control and at the protection of human health.     

两种重要登革热媒介蚊虫的种间竞争研究

目的　了解白纹伊蚊和埃及伊蚊的种间关系。方法　在温度 2 5～ 2 8℃、RH 65 %～ 80 %、光周期 (L∶D)12∶12的实验条件下 ,将两种伊蚊Ⅳ龄幼虫各 10 0条混合饲养 (亲代P0 ) ,用电动吸蚊器吸取各代成蚊约 10 0 0只进行分类观察。结果　在各代中 ,白纹伊蚊的种群数量大于埃及伊蚊 ,且随着传代次数的增加而增大 ,到子 2代 (P2 )时 ,该混合群落中已经观察不到埃及伊蚊。结论　白纹伊蚊和埃及伊蚊存在着激烈的种间竞争关系 ,并以白纹伊蚊优胜。     

Sampling study for larval density quantification of Aedes aegypti and Aedes albopictus in the state of S?o 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.     

Integration of Bacillus thuringiensis H-14 formulations and pyriproxyfen for the control of larvae of Aedes aegypti and Aedes albopictus

Studies were carried out on the bioefficacy and residual activity of Bacillus thuringiensis israelensis H-14 (Bti) (water-dispersible granules of VectoBac ABG 6511 and liquid formulations of VectoBac 12AS) and pyriproxyfen (insect growth regulator, Sumilarv 0.5%) as direct applications for control of larvae of Aedes aegypti and Aedes albopictus. Two dosages of each Bti formulation (285 and 570 international toxic units [ITU]/liter) and the integration of both Bti formulations and pyriproxyfen were used for residual tests with 45-liter earthen jars for a period of 4 wk. In 1 test series, the treated water was replenished daily with 6 liters of seasoned untreated water. In the 2nd test series, the water in the jars was topped up to the 40-liter level during evaluation. Neither Bti formulation remained effective for a full week. Water-dispersible Bti granules provided effective initial control activity against Ae. aegypti and Ae. albopictus for both test designs (with replenishment and without replenishment of water). The higher dosage (570 ITU/liter) for both Bti formulations was only partially effective at the end of 1 wk after being diluted. After 1 wk, water-dispersible Bti granules provided greater larval mortality than did liquid Bti formulation against both mosquito species when integrated with pyriproxyfen. Pyriproxyfen (79.5 and 159 mg/liter) on its own showed low larvicidal activity but provided very effective control of adult emergence. In this study, integration of Bti (285 and 570 ITU/liter) with pyriproxyfen (79.5 mg/liter) extended the duration of partial larval control somewhat, but live larvae persisted throughout the 4-wk test. The integration effect was more obvious when water-dispersible Bti granules were integrated with pyriproxyfen than when liquid Bti was used. Integration of Bti with pyriproxyfen had a negative effect on adult emergence, which was completely inhibited by pyriproxyfen after day 1. Daily replenishment of water increased Bti activity and provided slightly better larval control. Aedes albopictus and Ae. aegypti were both completely susceptible to the higher concentration of Bti and pyriproxyfen in both test designs (with replenishment and without replenishment of water).     

Tyrophagus putrescentiae predating adult insects of Aedes aegypti and Aedes albopictus in laboratory

The present study aimed at identifying a mite infesting a colony of Aedes aegypti and Ae. albopictus as well as investigating the source of infestation. The mite species was identified after it was mounted on slides in Hoyer's medium and examined under an optical microscope. It showed to be Tyrophagus putrescentiae. Fish and rabbit food samples were kept in an environmental chamber at 27 degrees C and 90% humidity for 21 days and were weekly examined. The presence of T. putrescentiae was only observed in rabbit food. It is assumed that T. putrescentiae had been introduced into the colonies through phoresy among guinea pigs, which were kept at the time near the insectary under favorable conditions for their development (28.7 degrees C, 72% humidity, photoperiod of 14L:10D hours).     

Ground application of AquaReslin and AquaKontrol against Anopheles quadrimaculatus, Aedes aegypti, and Aedes albopictus

Two permethrin formulations, AquaReslin and AquaKontrol, were applied by ultra-low volume truck-mounted sprayers on test plots under appropriate meteorological condition at Jacksonville, FL. The method of application was followed from the product label. The application rate for each formulation was 0.79 g permethrin per acre. AquaReslin and AquaKontrol demonstrated similar results against Anopheles quadrimaculatus; the former was superior to the latter used against Aedes aegypti, and Ae. albopictus. Teflon-coated standard glass slides were used to collect the aerosol components. Volume median-diameter droplets per square centimeter varied with pesticides and distance from spray source, and the mortality of the 3 species at 18 h ranged from 61.3% to 91.7%.     

Toxicity of permethrin-, malathion-, and fipronil-treated plant foliage to Aedes albopictus and Aedes aegypti

The toxicities of malathion-, permethrin-, and fipronil-treated plant foliage against laboratory colonies of adult Aedes aegypti and Aedes albopictus were evaluated. The exposure times significantly affected the percentage knockdown of mosquitoes. Fipronil-impregnated plant leaves caused higher mortality than malathion- and permethrin-impregnated leaves at the same application rates. Aedes albopictus was more sensitive to the 3 kinds of insecticides than Ae. aegypti. The method for bioassay of mosquito adulticides using plant foliage has been described, and the advantage and disadvantage of leaf bioassay method has been discussed and compared with other existing methods.     

Age-dependent bloodfeeding of Aedes aegypti and Aedes albopictus on artificial and living hosts

In order to quantify age-dependent acquisition of a bloodmeal, we compared bloodfeeding patterns of Aedes aegypti and Aedes albopictus starting from the time of first responsiveness to a bloodmeal up to 15 days postemergence. In separate experiments, cohorts of Ae. aegypti and Ae. albopictus of known age were offered their first bloodmeal from a silicon-membrane system or a restrained chicken. For cohorts ranging from 3 to 15 days old, the proportions feeding were significantly affected by species, age, feeding protocol, and the age x feeding protocol interaction. For both feeding protocols, a higher proportion of Ae. aegypti than Ae. albopictus, on average, consumed blood. Regressions of proportion feeding versus age indicated significantly positive slopes for Ae. albopictus and Ae. aegypti on the membrane system, and no significant relationship was observed for either species on the restrained chicken. Additionally, slopes for Aedes, as a group, fed on the membrane system were significantly different from those fed on the living host. For both Aedes species fed on the restrained chicken and for Ae. aegypti fed on the membrane system, the proportions feeding exhibited periodic patterns, with peaks approximately 2 days apart, suggesting possible control by endogenous rhythms.     

Differences in the larval alarm reaction in populations of Aedes aegypti and Aedes albopictus

The time spent submerged during the larval alarm reaction was measured for several strains of Aedes aegypti and Ae. albopictus from different locations. Differences between the 2 species were not significant. Differences in strains within the species were highly significant. Greater differences were seen among strains of Ae. albopictus than among strains of Ae. aegypti. These differences represent an additional indication of extensive local differentiation in Ae. albopictus.