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.     

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.     

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).     

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.     

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.     

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 3. Population fluctuations

Fluctuations in the adult Ae. aegypti and Ae. albopictus populations and their relationship to rainfall were studied by weekly collections from a number of stations in the city. Aedes aegypti populations generally fluctuated with the rainfall, with multiple peaks, except in the middle of the year when there was no increase in rainfall at the time of the peak in population. It is suggested that other regulating factors, in addition to rainfall, also determine the fluctuations of this species. Aedes albopictus also fluctuated, with three peaks in a year, and these bore a close relationship to rainfall.     

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 2. Larval habitats

Detailed information on the breeding habitats of Ae. aegypti and Ae. albopictus is necessary when planning programmes for their control. The larval habitats of the two species in 10 city areas were counted and classified according to type, frequency of occurrence, location, and function. Of all the breeding habitats recorded 95% were domestic containers. The most common Ae. aegypti breeding habitats were ant traps, earthenware jars, bowls, tanks, tin cans, and drums, ant traps being the most common indoors and earthenware jars the most common out doors. Breeding habitats for Ae. albopictus were commonly found in earthen ware jars, tin cans, ant traps, rubber tires, bowls, and drums; ant traps were the most common indoor habitat and tin cans were most common outdoors.     

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 1. Distribution and density

The distribution and density of Ae. aegypti and Ae. albopictus in Singapore were assessed from extensive larval surveys carried out from 1966 to 1968 to evaluate their respective roles in the epidemiology of dengue haemorrhagic fever and to study their ecology in the urban areas. Ten urban areas where the majority of dengue haemorrhagic fever cases occurred were surveyed.     

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 4. Competition between species

There is a current belief stemming from statements made in the literature that Ae. aegypti is displacing Ae. albopictus in a number of cities of South-East Asia and in Calcutta, India. A critical review of these works showed that either the observations were inconclusive or the methods of collection were biased for one or the other species.     

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。     

Aedes aegypti (L.) and Aedes albopictus (Skuse) in Singapore City. 5. Observations in relation to dengue haemorrhagic fever

Dengue haemorrhagic fever in Singapore was a disease of the urban human population, with concentrations of cases occurring in areas of high population density. Mosquito surveys revealed that these areas also had high population densities of Ae. aegypti and 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.     

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.     

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.     

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.     

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.