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.     

Relative suitability of Aedes albopictus and Aedes aegypti in North Carolina to support development of Dirofilaria immitis

The relative suitability of two colonies established from local strains of Aedes albopictus (Wilmington and Rockingham) and a local (Raleigh) and laboratory (Liverpool) strain of Ae. aegypti to support development of Dirofilaria immitis was investigated. High levels of mortality occurred 1-2 days after mosquitoes fed on a heavily microfilaremic (28,617 microfilariae/ml) dog but not when mosquitoes were fed on a dog exhibiting a moderate microfilaremia (3,300 microfilariae/ml). At 15-16 days postfeeding, development of D. immitis to the third larval stage occurred to some extent in mosquitoes of all four strains. Microfilariae were only found in the Raleigh strain of Ae. aegypti. Aedes albopictus most frequently contained first and second stage larvae that were deteriorated which suggested that their development had been arrested. Third stage larvae were found most often in the Liverpool strain of Ae. aegypti. Colonies established from local strains of Ae. albopictus and Ae. aegypti do not appear to be suitable hosts of D. immitis.     

Infection and dissemination of dengue virus type 2 in Aedes aegypti, Aedes albopictus, and Aedes scutellaris from the Torres Strait, Australia

To determine their relative roles in transmission of dengue virus (DENV) in the Torres Strait region of northern Australia, we examined infection and dissemination of a sympatric strain of dengue virus type 2 (DENV-2) in Aedes scutellaris, Ae. albopictus, and Ae. aegypti. In experiments using membrane feeders for virus exposure, infection rates were 83% and 43% for Ae. scutellaris and Ae. aegypti, respectively. Salivary gland infection rates for both species were 43%. In experiments using pledgets for virus exposure, infection rates for Ae. aegypti, Ae. scutellaris, and Ae. albopictus were 68%, 55%, and 37%, respectively. Aedes albopictus exhibited the greatest barriers to infection with only 7% tested developing a salivary gland infection, compared to 42% and 24% of Ae. aegypti and Ae. scutellaris, respectively. These results suggest that Ae. scutellaris may have been responsible for DENV transmission on Torres Strait islands, where Ae. aegypti does not occur. In contrast, Ae. albopictus may not be an important vector of DENV-2 from the Torres Strait.     

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.     

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.     

Vector competence of Aedes albopictus from Houston, Texas, for dengue serotypes 1 to 4, yellow fever and Ross River viruses

A combination of virus infection and transmission experiments showed that a Houston, Texas strain of Aedes albopictus is a competent vector for dengue (DEN), yellow fever (YF) and Ross River (RR) viruses. However, at 14 days incubation, DEN virus infection rates in a Puerto Rican strain of Aedes aegypti were significantly higher for each of the four DEN serotypes, except DEN-1, than in Houston Ae. albopictus fed simultaneously on the same virus suspensions. The degree of correlation between disseminated DEN infection rates in Houston Ae. albopictus and transmission to an in vitro system ranged from 42 to 88% for the four DEN serotypes. No significant difference was noted in YF virus infection rates or transmission rates in the two mosquito species fed on the same virus suspensions and incubated for the same time period. Also, RR virus infection and transmission rates in Houston and Hawaiian strains of Ae. albopictus were generally comparable.     

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.     

Susceptibility of laboratory and field-collected Aedes aegypti and Aedes albopictus to Bacillus thuringiensis israelensis H-14

Susceptibility levels of a few laboratory-cultured and dengue-endemic area field-collected strains of Aedes aegypti and Aedes albopictus to Bacillus thuringiensis israelensis (Bti) at different storage ages were studied. The susceptibility of laboratory-cultured World Health Organization (WHO) Bora Bora reference, Vector Control Research Unit (VCRU), and Fumakilla Malaysia Berhad (FMB) strains of Ae. aegypti to Bti was examined. The sensitivity to Bti decreased with storage age. The median lethal concentration (LC50) for Bti increased by 2-3 times after 2 years compared to a fresh sample (3-6 months of storage). However, after the 2-year storage period, Bti still provided very good efficacy against all laboratory-cultured susceptible strains of Ae. aegypti and Ae. albopictus. The observed 95% lethal concentration values were about 20 times lower than the recommended concentration (6,000 international toxic units (ITU)/liter). Results obtained from the study against the dengue-endemic area field-collected strains of Ae. aegypti and Ae. albopictus confirmed the effectiveness of the Bti after storage for 2 years (18-24 months). For Ae. aegypti, the Ujung Batu strain was the most susceptible to Bti, whereas the Sungai Nibong strain showed the most tolerance. Susceptibility of laboratory-cultured strains varied; the Air Itam strain of Ae. albopictus was the most susceptible to Bti, whereas the Kampung Serani strain was the most tolerant among the field strains. However, the laboratory strain of Ae. albopictus was more susceptible than all the field strains.     

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.     

A comparison of seven traps used for collection of Aedes albopictus and Aedes aegypti originating from a large tire repository in Harris County (Houston), Texas

Among 7 traps tested, significantly higher (P < 0.01) mean numbers of Aedes albopictus (269) and Aedes aegypti (55) females were collected within the Mosquito Magnet Liberty trap compared with the remaining traps. The second highest mean captures for both species were obtained from omnidirectional Fay-Prince (77 Ae. albopictus) and Dragonfly (13 Ae. aegypti) traps, which were not significantly different (P > 0.01) from an experimental moving-target trap that produced mean captures of 40 Ae. albopictus and 6 Ae. aegypti (alpha = 0.01). In terms of Ae. albopictus capture, no significant differences (P > 0.01) existed between Dragonfly, CDC without light (CDC -), and CDC with light (CDC +) captures, which were significantly different (P < 0.01) from Mosquito Deleto. No statistical significance existed between moving-target, omnidirectional, CDC +, CDC -, and Mosquito Deleto traps in terms of Ae. aegypti capture (P > 0.01), individual trap positions, or number of Ae. albopictus and Ae. aegypti females collected throughout the 21-day test (P > 0.05). Mosquito Magnet Liberty collected 7,208 Ae. albopictus, 1467 Ae. aegypti, and 13 other species representing 5 genera, which comprised the largest total (9662) and percentage (62.5%) of mosquitoes collected by all traps combined. Omnidirectional and moving-target traps captured 1941 and 1050 Ae. albopictus, 138 and 220 Ae. aegypti, and 2171 (14.0%) and 1397 (9.0%) of the total mosquitoes captured by all traps, with 8 and 10 species representing 5 genera, respectively, included in these collections. The Dragonfly captured 476 Ae. albopictus, 376 Ae. aegypti, and 1008 total specimens (6.5%) representing 8 species and 4 genera in these collections. CDC + and CDC - traps collected nearly identical numbers of Ae. albopictus (431, 450) and Ae. aegypti (71, 71) with 537 (3.4%) and 551 (3.5%) total specimens, respectively. Eight species representing 5 genera were captured from CDC +, whereas CDC - captured 6 species representing 4 genera. Mosquito Deleto captured 118 mosquitoes, including 19 Ae. albopictus and 62 Ae. aegypti females (0.7%), with 6 species representing 4 genera. Battery-powered traps with contrasting color schemes and movement worked considerably better than stationary CDC miniatures without color or movement. Omnidirectional Fay-Prince and moving-target traps without octenol captured Ae. albopictus and Ae. aegypti females as frequently as some commercial traps. Additionally, costs incurred per mosquito trapped, future trap design, and important consumer-centered issues are briefly discussed.     

Long-term surveillance data and patterns of invasion by Aedes albopictus in Florida

We used geographic information system (GIS) and long-term mosquito surveillance data from Lake, Pasco, Manatee, and Sarasota Counties, FL, to look at patterns of invasion by Aedes albopictus and concurrent changes in resident Ae. aegypti. We investigated environmental factors associated with population changes in these species with the use of satellite climate data. Aedes aegypti densities attenuated rapidly following the arrival of Ae. albopictus in most counties, yet both species persisted in equilibrium in Manatee County. We discuss the relative importance of rainfall, habitat, and proximity to urban areas in the population dynamics of these species in sympatry.     

Susceptibility of adult field strains of Aedes aegypti and Aedes albopictus in Singapore to pirimiphos-methyl and permethrin

The susceptibilities of field strains (Fl) of Aedes aegypti and Ae. albopictus adult females to pirimiphos-methyl and permethrin were investigated and compared with a susceptible laboratory strain (S) by using a filter paper (12 x 15 cm) impregnation method. The resistance ratio between the 50% lethal concentration values (RR50) of the Fl and the S strains shows that the RR50 of Fl Ae. aegypti for pirimiphos-methyl was 1.5 and the RR50 of Fl Ae. aegypti for permethrin was 12.9. The RR50 of Fl Ae. albopictus for pirimiphos-methyl was 1.4, and that for permethrin was 1.8. This indicates that the field strain Ae. aegypti, but not Ae. albopictus, has developed resistance to permethrin. However, both species are still susceptible to pirimiphos-methyl. Therefore, control with pirimiphos-methyl will still be effective.     

Comparison of blood feeding response and infection of Aedes aegypti to Wuchereria bancrofti using animal membranes and direct host contact

Comparison of an artificial, whole-blood membrane feeding procedure was performed by feeding Aedes aegypti (Liverpool strain) on the blood of patients infected with Wuchereria bancrofti microfilariae with the use of 3 types of membranes produced from chicken and mouse skin and swine intestine. Direct feeding of Ae. aegypti on the skin of infected human patients served as control. For all 3 types of membranes, mosquito survival, infection, and number of infective-stage larvae per mosquito did not differ significantly from the control. However, the blood feeding response between swine intestine layer (32%) compared to chicken skin (75.3%), mouse skin (70%), and direct feeding (84%) differed significantly. The response in direct feeding method was significantly higher than those in all membranes tested (F = 18.89; df = 3; P < 0.05) Chicken skin preparation was shown to be the preferred membrane for blood feeding Ae. aegypti and experimental infection with W. bancrofti.     

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.     

Invasion of cemeteries in Florida by Aedes albopictus.

Aedes albopictus has been found in 53 of the 67 Florida counties. The initial discoveries in 11 of these counties were made in cemeteries. At several locations, Ae. albopictus became well-established in cemeteries before appearing in nearby accumulations of waste tires. The recycling of plastic floral baskets may be aiding the spread of Ae. albopictus. Mosquitoes were commonly found in all types of flower-holding containers in cemeteries, except bronze vases. In the laboratory, most Aedes aegypti eggs laid in bronze vases hatched, but larvae subsequently died. The spread of Ae. albopictus in cemeteries seems to occur at the expense of Ae. aegypti populations. At one cemetery immature Ae. albopictus and Ae. aegypti were found in about 70% of the Aedes-positive containers at the start of a monitoring program. In subsequent collections from this site, Ae. albopictus was found in nearly all Aedes-positive containers, whereas there was a progressive decrease in containers with Ae. aegypti. This trend did not appear to be the result of any seasonal pattern because in a nearby cemetery where Ae. albopictus was absent, Ae. aegypti did not show a similar decline. Limiting flower-holding containers to those with drain holes or to bronze vases would greatly limit mosquito production.     

Vector competence of geographic strains of Aedes albopictus and Aedes polynesiensis and certain other Aedes (Stegomyia) mosquitoes for Ross River virus

The vector competence of geographic strains of Aedes albopictus and Ae. polynesiensis and Fiji strains of Ae. pseudoscutellaris and Ae. aegypti was assessed for Ross River (RR) virus, the etiologic agent of epidemic polyarthritis. Strains of Ae. polynesiensis from Fiji, Rarotonga, Somoa and Tahiti were the most susceptible to infection per os (MID50 less than or equal to 10(1.2) Vero cell plaque-forming units [PFU]/blood meal). Virus transmission data were variable, but all strains except the one from Fiji transmitted virus at 14 to 21 days postinfection. Shanghai and Hawaii Ae. albopictus and Fiji Ae. pseudoscutellaris were also highly susceptible to per os infection with RR virus (MID50 10(2.0) to 10(2.6) PFU). Singapore and Sri Lanka Ae. albopictus and Fiji Ae. aegypti were the least susceptible (MID50 10(4.0) to 10(4.2) PFU). With one exception, virus transmission rates for Ae. pseudoscutellaris and Ae. aegypti and the four strains of Ae. albopictus ranged from 52 to 100%. A total of 4,718 third- and fourth-instar larvae from the second gonotrophic cycle of potentially infected females were tested for RR virus in 39 pools. Infection rates in parental females ranged from 87 to 100% in Ae. albopictus, Ae. pseudoscutellaris and Ae. polynesiensis and 40 to 48% in Ae. aegypti. Virus was not isolated from larval progeny.     

不同动物(血)对蚊虫的引诱作用

目的比较不同动物及动物血液对蚊虫的引诱作用,探讨蚊虫对动物宿主的嗜血习性。方法以不同动物血液引诱实验室饲养的蚊虫,以不同动物进行野外现场引诱蚊虫实验。结果实验室内淡色库蚊对猪血的吸血率最高,为51%,其他依次为人血、狗血、绵羊血和牛血;白纹伊蚊对牛血吸血率最高,为47%,其他依次为绵羊血、狗血、人血和猪血;埃及伊蚊对牛血吸血率也最高,为44%,其他依次为狗血、绵羊血、人血和猪血。现场实验表明家鸡对淡色库蚊引诱力较强,共诱集到1420只,其他依次为肉鸽、麻雀和大白鼠;家鸡对白纹伊蚊引诱力较强,共诱集到11只,其他依次为大白鼠、肉鸽和麻雀。结论淡色库蚊嗜吸猪血,白纹伊蚊、埃及伊蚊嗜吸牛血;家鸡对淡色库蚊的引诱效果较好。     

First record of Ascogregarina taiwanensis (Apicomplexa: Lecudinidae) in North American Aedes albopictus

Aedes albopictus collected in the East St. Louis, Illinois, area were found infected with the gregarine protozoan, Ascogregarina taiwanensis. Infection rates varied from 67 to 95% at 4 sites and 0 to 10% at 2 others. Lower infection levels were found in Ae. epactius (42%) and Culex restuans (one larva). Four mosquito species were cross-infected in the laboratory with gregarines isolated from field-collected hosts. Aedes atropalpus was 90% susceptible to A. taiwanensis (100% in Ae. albopictus), with abnormal development and some melanization of trophozoites and gametocysts. In Ae. aegypti and Cx. restuans, the experimental infection was much lower (12-56%) and exhibited abnormalities similar to the Ae. atropalpus infections. Ascogregarina oocysts recovered from both Ae. aegypti and Ae. atropalpus hosts were subsequently infective to Ae. albopictus. In Ae. triseriatus, A. taiwanensis infection was very low (25%, 1-2 trophozoites per larva); gametocysts were not observed nor were infectious oocysts obtained. We conclude that A. taiwanensis, newly introduced to the USA with Ae. albopictus, can develop in 4 indigenous mosquito species and can produce deleterious effects in at least 2, Ae. aegypti and Ae. atropalpus.     

Evaluation of cyclopoid copepods for Aedes albopictus control in tires

Six species of cyclopoid copepods in New Orleans were tested for biological control of Aedes albopictus larvae in discarded tires. Six to 8 weeks after introduction, Diacyclops navus, Acanthocyclops vernalis, Mesocyclops ruttneri and Mesocyclops edax reduced the number of Ae. albopictus larvae by 83, 90, 95 and 96%, respectively. Macrocyclops albidus and Mesocyclops longisetus were the most effective species. Six to 8 weeks after introduction, Macrocyclops albidus reduced Ae. albopictus larvae by 99%. Three months after introduction Macrocyclops albidus reduced Ae. albopictus larvae by 100%, and Mesocyclops longisetus reduced Ae. albopictus larvae by 99.8%. Macrocyclops albidus and Mesocyclops longisetus were equally effective at eliminating Ae. aegypti and Ae. triseriatus larvae.