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The presence of Aedes albopictus (Skuse) was recently confirmed for the first time in northwestern Greece. This location is within the distribution range of a morphologically similar species, Aedes cretinus Edwards, and is a potentially favorable region for the reintroduction of Aedes aegypti (L.). It was thus compelling to use methods in addition to morphology-based keys to correctly identify specimens badly damaged, rubbed, or otherwise altered in their external characteristics. It was decided to use molecular techniques as a novel and reliable method for differentiating the three Stegomyia species. The nuclear internal transcribed spacer 2 (ITS2) fragments from morphologically identified Ae. albopictus and Ae. cretinus specimens were amplified, and their sequences were compared with those in GenBank for Ae. albopictus, Ae. cretinus, and Ae. aegypti. Also, mitochondrial cytochrome oxidase I (COI) fragments were amplified for Ae. albopictus and Ae. cretinus (so far not available in GenBank) and compared with Ae. aegypti fragments. ITS2 and COI sequences generated in our study were deposited in GenBank and could be useful in future studies of mosquitoes by other research workers.
Aedes triseriatus (Say) (Diptera: Culicidae), the major vector of La Crosse (LAC) virus, efficiently transmits LAC virus both horizontally and transovarially. We compared the vector competence and transovarial transmission ability of Ae. triseriatus, Aedes albopictus Skuse, and Aedes aegypti (L.) for LAC virus. Ae. triseriatus and Ae. albopictus were significantly more susceptible to oral infection with LAC virus than Ae. aegypti. The three species also differed in oral and disseminated infection rates (DIRs). Transovarial transmission (TOT) rates and filial infection rates (FIRs) were greater for Ae. triseriatus than either Ae. albopictus or Ae. aegypti. These measures were integrated into a single numerical score, the transmission amplification potential (TAP) for each species. Differences in TAP scores were due mainly to the differences in DIRs and FIRs among these mosquitoes. Although the TAP score for Ae. albopictus was lower than that of Ae. triseriatus, it was 10-fold greater than that for Ae. aegypti.
Bluetongue virus multiplied in cell lines derived from Aedes albopictus and Aedes pseudoscutellaris cells. Virus reached a maximum titre in the Ae. pseudoscutellaris cells three days post inoculation, and in Ae. albopictus cells six days p.i. Virus growth was demonstrated in both cell lines at 27 degrees C and 37 degrees C. Significant titres of virus were still present in the Ae. albopictus cells after five subcultures at 27 degrees C over a period of six weeks. No cytopathic effect was observed in either cell line. A third cell line derived from the mosquito Ae. aegypti did not support the growth of Bluetongue virus.
The paper reports some observations on the subgenus Aedes (genus Aedes, Diptera, Culicidae) in northeast Italy. Two species were collected: Ae. cinereus and Ae. geminus, the latter recorded for the first time in Italy. Morphological, ecological and biological data of the two species are presented. The identification is possible only on the male hypopigium; larvae, pupae and adult females show no differential characters. For both species, the larval breeding sites were fresh water marshes mainly within woods; preimaginal development took place twice a year, in Spring and Autumn. The females were strongly anthropophilic. No biological differences between the two species were noticed, but more data are needed to ascertain their relationships and the presence of subtle biological divergences.
The time course and pattern of the replication and dissemination of La Crosse virus was studied in orally infected Aedes triseriatus (Say) and Ae. hendersoni Cockerell. Development of La Crosse virus was approximately the same in both species when plaque assay titers of intact mosquitos or dissected tissues were compared. The mosquitoes were equally susceptible to infection; all Ae. hendersoni and 99% of the Ae. triseriatus tested showed detectable midgut infections. Virus was first detected in hemolymph, salivary glands, and ovaries 10-13 d after infection in both species. The pattern of infection suggests virus dissemination beyond the midgut to be via the hemolymph. By 21 d after infection, 100% (10 of 10) of Ae. triseriatus and 70% (7 of 10) of Ae. hendersoni had infected salivary glands, and the geometric mean titer of Ae. hendersoni salivary glands was 10 times higher than the geometric mean titer of those of Ae. triseriatus, However, when tested for transmission 22 d after infection by refeeding on suckling mice, only 9% (2 of 22) of the Ae. hendersoni with disseminated infections transmitted virus versus 71% (12 of 17) of the Ae. triseriatus. A salivary gland escape barrier was shown to be primarily responsible for the failure of Ae. hendersoni to orally transmit La Crosse virus. However, eight parenterally infected Ae. hendersoni females transovarially transmitted the virus to 25% (5 of 20) of their progeny.
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.
Morphology and behavior of chromosomes and development of testes and sperm were examined in hybrids from interspecific crosses involving Aedes cooki and four sibling species of the Aedes (Stegomyia) scutellaris subgroup of mosquitoes. The degree of abnormality in hybrid spermatogenesis in interspecific crosses involving Aedes cooki males and females of four sibling species paralleled the geographic distributions of these species and the genetic divergence indicated by other genetic studies. Hybrids from crosses involving Aedes malayensis females and Aedes cooki males were characterized by atrophied testes and extensive chromosome breakage. Hybrids from crosses involving Aedes alcasidi females and Aedes cooki males suggested a possible pericentric inversion distinguishing the largest autosome of Aedes alcasidi from that of Aedes cooki. Hybrids from interspecific crosses involving females of Aedes polynesiensis and Aedes pseudoscutellaris and males of Aedes cooki showed high percentages of univalents of the smallest chromosome pair. Hybrid spermatogenesis in two interspecific crosses involving Aedes cooki females differed from results of reciprocal crosses. Data were scant, however, and interpretation was difficult in view of negligible hatch in all interspecific crosses involving Aedes cooki females.
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.
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 Iguaçu, 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.
Previous studies have demonstrated that the synthesis of juvenile hormone (JH) by the isolated corpora allata (CA) complex in vitro as well as the JH titer in the yellow fever mosquito Aedes aegypti are elevated before feeding and low after a blood meal. In the present study, we used an in vitro radiochemical assay to analyze the effect of farnesoic acid (FA) and Aedes allatotropin (Aedes-AT) on the biosynthesis of JH and methyl farnesoate (MF) by the isolated CA complex of A. aegypti adult female. CA complex from day-0 females (0-1 h after emergence) exhibited a low basal juvenile hormone III (JH III) biosynthetic activity and did not respond to either allatotropic or FA stimulation. However, incubation of CA complexes from newly emerged females with Aedes-AT plus FA resulted in very high production of JH III. This is the first report suggesting that allatotropin makes corpora allata in newly emerged females capable for JH biosynthesis. When we studied CA complexes dissected from females 1 day after emergence, the stimulatory action of Aedes-AT was strong and dose-dependent, with maximum stimulation in the range of 10(-8)-10(-9) mol l(-1), suggesting that Aedes-AT is indeed a true allatotropin (a molecule with allatotropic activity) in A. aegypti. The addition to the culture medium of 40 micro mol l(-1) FA, a JH precursor, resulted in a 9-fold increase in JH III biosynthesis in 2-, 4- and 6-day-old sugar-fed females. The two major labeled products synthesized by the stimulated CA complex were identified as JH III and MF by RP-HPLC and GC-MS. Treatment of CA complexes with FA, but not Aedes-AT, resulted in an increase in MF. Application of both Aedes-AT and FA to the CA complexes of 2-, 4- and 6-day-old females resulted in the same effects as FA alone. These data suggest that in sugar-fed females, FA and Aedes-AT exert different effects on the terminal steps in JH biosynthesis.
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The breeding habitats of the dengue vector, Aedes aegypti and Aedes albopictus, were studied using larval collection method inside and outside houses in 6 villages of Barru, South Sulawesi, Indonesia from July 1994 to August 1995. Aedes aegypti was the dominant species, being abundant indoors especially in the coastal areas. Aedes albopictus was breeding primarily in outdoor containers in the hill and mountain areas. Earthen jar was the most common breeding habitat of Aedes aegypti in all villages surveyed. Drum can was the most common outdoor breeding habitat of Aedes albopictus in the hill and mountain areas. The high Breteau indices of Aedes aegypti and Aedes albopictus suggests that these species may play an important role in the transmission of dengue hemorrhagic fever in Barru where epidemics of the fever occur occasionally.