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.     

Observations on possible competitive displacement between populations of Aedes aegypti Linnaeus and Aedes albopictus Skuse in Calcutta

The possibility of competitive displacement in Calcutta between Aedes aegypti, a known vector of arboviruses, and A. albopictus, a suspected vector, was explored by general collections of immature stages from all types of breeding-places and by exposing oviposition traps in tenement houses, and gardens in urban, suburban, and rural environments. A. aegypti was predominant in houses and tenements in urban areas, but A. albopictus was not excluded. Both species occurred in about equal densities in small urban gardens. In suburban and rural areas, A. albopictus was predominant, or the only one of the two species present. It readily entered houses for the purpose of oviposition, especially in the absence of A. aegypti.     

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.     

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.     

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。     

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.     

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).     

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.     

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.     

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.     

Frequency of Aedes aegypti and Aedes albopictus larvae and pupae in traps, Brazil

OBJECTIVE: To evaluate the monthly frequency of larvae and pupae of Aedes albopictus, Aedes aegypti and other mosquitoe species in tires, and the influence of environmental factors on that. METHODS: The immature stages of mosquitoes were collected monthly from four tires in the municipality of Nova Igua?u, Brazil, from November 1997 to October 1998. The following variables were measured: rainfall, temperature, water volume, water pH. The tires were arranged in a pyramid, one at the base (tire 1) and 3 others (2,3 e 4) laying over it. RESULTS: Were collected 10,310 larvae and 612 pupae. Aedes albopictus was the most common species in both the larval and pupal stages. Aedes aegypti and Aedes albopictus were collected throughout the year but were more frequent during in the rainy season. The number of Aedes aegypti was significantly correlated with the temperature, rainfall and water volume of the tires. The correlation between water pH and number of larvae was not significant. Aedes albopictus larvae were more frequent in tires left in the shade. CONCLUSIONS: Aedes albopictus was more abundant in tires than Aedes aegypti. Discarded tires seem to be an important source of both Aedes species throughout the year. The favored environmental conditions of the tires, such as water volume and exposure to sunlight differ for Aedes albopictus and Aedes aegypti.     

Susceptibility to organophosphate insecticides in larval Aedes albopictus

Larvae of 26 strains of Aedes albopictus were tested for susceptibility to 5 organophosphate insecticides. The recently collected geographic strains included 13 from the USA, 5 from Brazil, 3 from Southeast Asia and 5 from Japan. The greatest amount of variability was seen among U.S. populations, ranging from quite susceptible to potentially resistant. Brazilian samples were generally quite susceptible to all insecticides tested. Three Japanese strains showed tolerance or low level resistance to fenitrothion (2X, 3X and 8X), as did 2 U.S. strains (3X and 5X). Two U.S. strains showed tolerance to malathion (3X and 4X), while one strain from Chicago, Illinois, showed low level resistance (22X). Selection for resistance to malathion in a laboratory strain composed of multiple U.S. geographic strains resulted in a resistance ratio of 21X after 6 generations of selection.     

Interspecific mating between Louisiana strains of Aedes albopictus and Aedes aegypti in the field and laboratory

Interspecific mating between Aedes albopictus males and Ae. aegypti females was detected in the field using mark-release-recapture techniques. By 3 days after the release of virgin Ae. aegypti females into a field site containing only Ae. albopictus, 100% of the captured females were inseminated. Laboratory investigations indicated that male Ae. albopictus were very proficient at inseminating Ae. aegypti females and that Ae. aegypti males rarely inseminated Ae. albopictus females, especially if Ae. aegypti females were available. Most of the Ae. aegypti females inseminated by Ae. albopictus males contained only small amounts of dead sperm in their spermathecae, while inseminated females from the converse interspecific mating and from intraspecific matings contained only large amounts of live sperm. The results are discussed in relation to the decline in Ae. aegypti densities observed since the introduction of Ae. albopictus into the southern USA.     

The magnitude of seasonal changes in larval populations of Aedes aegypti in Bangkok, Thailand

Weekly surveys of Aedes aegypti larvae were made during 1966-67 in three localities in Bangkok in order to detect and measure any changes in the population which might be correlated with the seasons. The larval habitats were divided into water-jars and miscellaneous containers. Only the data from alternate weekly surveys were analysed. Analysis of variance showed that the changes in the numbers of habitats occupied varied greatly both by month and by locality. It is concluded that there was some reduction in the larval population during the cool and hot seasons and that the magnitude and timing of the fall varied from place to place. The reduction was of the order of 11%-26%. Local environmental changes, as well as climatic changes, greatly influenced the Ae. aegypti population.     

Anthropophilic activity of Aedes aegypti and of Aedes albopictus in area under control and surveillance

OBJECTIVE: To describe the hematophagous activity of Ae. aegypti and Ae. albopictus in an area under control and surveillance. METHODS: The study was conducted during 18 months, from April, 1993 to October, 1994, in Cosmopolis, Sao Paulo state, Brazil. Human baits were used to collect mosquitoes. The number of females captured is presented monthly by area of the city and local in the household. The rainfall was measured and indices are presented without model adjustment. RESULTS: The presence of females of both species was observed in 83% (Ae albopictus) and 61% (Ae. aegypti) of the period studied. The months of January, February and March presented the highest rates of activity for females of both species, with Ae. albopictus being more frequently captured than Ae. aegypti. Both species were captured in central and peripheral areas of the city, during the day from 9 to 12 am and from 4 to 7 pm. By a Poisson regression, it was observed that Ae. albopictus females were more frequently captured in the peri-housed area, in an independent way considering the area of the city. CONCLUSIONS: It has been identified difference on the hematophagous activity only for Ae. albopictus, being of importance the outside area of the house.     

灭蚊幼缓释包防治白纹伊蚊幼虫的研究

目的评价倍硫磷缓释包防治白纹伊蚊幼虫的效果。方法应用生物测试法测定药剂敏感性,气相色谱法测定药物释出浓度,模拟现场法评价防治效果。结果广州市各地区的白纹伊蚊幼虫对倍硫磷敏感,抗性倍数均在2以下。在半年内,不换水情况下投放在2 L水中倍硫磷颗粒剂和倍硫磷缓释包平均释出药物分别为5.73和0.242 mg/L,变异系数分别为50.12%和40.33%;每周换1次水情况下投放在2 L水中倍硫磷颗粒剂和倍硫磷缓释包平均释出药物分别为1.965和0.087 3 mg/L,变异系数分别为215.73%和92.21%;两种包裹方式均能致死受试的试虫,但缓释包比颗粒剂释出药物更稳定;倍硫磷缓释包控制野外小型积水容器的白纹伊蚊幼虫可长达1年以上,而颗粒剂只有不到半年的防效。结论倍硫磷缓释包适合广州地区白纹伊蚊的应急控制。     

Diversity of oviposition containers and buildings where Aedes albopictus and Aedes aegypti can be found

OBJECTIVE: To assess the diversity of oviposition containers and buildings where females of Aedes albopictus and Aedes aegypti can be found. METHODS: A study was carried out in the city of Rio de Janeiro, Southern Brazil, between 2002 and 2003. Larvae in different types of buildings were investigated, and immature forms found were then sent to the laboratory for identification. The larval frequency for both mosquitoes was estimated in the oviposition containers available. The Breteau index and the building infestation index were calculated and differences were tested using the Chi-square test. RESULTS: The types of buildings that were positive for Aedes albopictus and Aedes aegypti were: dwellings (83.9%); churches, schools, clubs (6.8%); vacant land (6.4%); and businesses (2.8%). Of 9,153 larvae collected, 12.0% were Aedes albopictus and 88.0% were Aedes aegypti. Aedes albopictus were mostly found in drains (25.4%); cans, bottles, empty bottles (23.9%); and plant vases (16.2%). Aedes aegypti was much more frequently found than Aedes albopictus (chi(2)=145.067; p<0.001). Both species were significantly more frequent in artificial than in natural oviposition containers (chi(2)=31.46; p<0.001). The building infestation index and Breteau index for Aedes albopictus were 0.3% and 0.28% in 2002 and 0.4% and 0.5 in 2003, respectively. For Aedes aegypti, they were 1.0%, 1.16 in 2002 and 3.5% and 4.35 in 2003, respectively. CONCLUSIONS: The present study assessed the frequencies of Aedes albopictus and Aedes aegypti females in various types of oviposition containers and types of buildings. The abundant availability of artificial containers in dwellings, associated with the capacity of Ae. albopictus to be also found in natural oviposition containers, has greatly contributed for their gradual adaptation to human environment.     

Seasonal changes in the larval populations of Aedes aegypti in two biotopes in Dar es Salaam, Tanzania

The seasonal dynamics of larval populations of Aedes aegypti was studied in two different biotopes in Dar es Salaam, Tanzania. The first biotope was located on the Msasani peninsula on the coast 6 km north of Dar es Salaam, where A. aegypti breeds exclusively in coral rock holes. The population dynamics was studied during both the rainy and the dry season. Seasonal changes in the density of A. aegypti larvae depend primarily on variation in rainfall. The population of larvae dropped to zero only for a short time during the driest period while the adult population was maintained at a low level. The second biotope was in an automobile dump in a Dar es Salaam suburb, where A. aegypti breeds in artificial containers such as tires, automobile parts, tins, coconut shells, and snail shells. The greater part of the A. aegypti population of this biotope is maintained in the egg stage during the dry season. It serves as a focal point for breeding during the dry season: with the coming of the rains, the population expands into the surrounding residential areas. More than 70% of the larval population developed in tires, 20% in tins, 5% in coconut shells, and 1% in snail shells.