[Aedes albopictus (Skuse) (Diptera, Culicidae) in eastern Veneto]

A survey was carried out in autumn 1992 and spring-autumn 1993 to study the seasonal distribution and the dispersal of Aedes albopictus (Skuse) in Portogruaro (province of Venice; North-Eastern Italy). Larvae and pupae were found from May through September; the larvae hatching from eggs after the end of September seemed unable to complete development. The adults bit until October. The mosquito spread in new areas of Portogruaro town, even after insecticidal treatments. Private areas seemed to play an important role in the preservation of the infestation, as they were not treated by the public pest control service.

Synergism of mosquitocidal toxicity between CytA and CryIVD proteins using inclusions produced from cloned genes of Bacillus thuringiensis

The toxicity to mosquito larvae of the parasporal body produced by Bacillus thuringiensis subsp. israelensis and the PG-14 isolate of B. thuringiensis subsp. morrisoni is at least 20-fold greater than any of the four mosquitocidal proteins of which it is composed (CytA, CryIVA, B, and D). This high toxicity is postulated to be due to synergistic interactions among parasporal proteins. However, this remains controversial because values reported for the specific toxicity of individual proteins, especially the CytA protein, vary widely owing to the methods used to purify and assay toxins against larvae. In an attempt to resolve questions of purity, specific toxicity, and synergism, individual genes encoding the CytA and CryIVD toxins were cloned and expressed in acrystalliferous B. thuringiensis subsp. israelensis cells using the shuttle vector pHT3101. CytA and CryIVD inclusions were purified and their toxicity was determined alone and when combined at different ratios using bioassays against first instars of Aedes aegypti. The LC50 for the CytA inclusion was 60 ng ml-1, whereas the LC50 for the CryIVD was 85 ng ml-1. In comparison, the LC50s for different combinations of CytA and CryIVD inclusions ranged from 12-15 ng ml-1, 4-5 times higher than the toxicity of either protein alone, demonstrating marked synergism between these two proteins. These results suggest that the high toxicity of the wild-type parasporal bodies of B. thuringiensis subspp. israelensis and morrisoni is due to synergism among three or four of their major proteins.

Field studies on populations of Aedes albopictus and Toxorhynchites species in bamboo pots in Malaysia

Between April 1987 and March 1988, populations of immature Aedes albopictus and Toxorhynchites spp. in bamboo pots were sampled weekly. Populations of Ae. albopictus and rainfall varied from month to month. During the heavy rainfall months of September and October 1987, larval counts of Ae. albopictus were high, between 30.8 and 49.2 larvae per week compared to 16 larvae per week during the low rainfall month of January 1988. A higher population of Toxorhynchites spp. was associated with a low population of the vector.

Quantitative sampling of immature Aedes aegypti in metal drums using sweep net and dipping methods

The behavior of aquatic stages of Aedes aegypti was evaluated in 200-liter metal drums to develop improved surveillance. When known numbers of larvae recovered with a rectangular net and with a standard dipper were compared, all stages except 1st instar were most numerous in the top 1/3 of the drum. Water temperature was the only significant variable affecting the vertical distribution of 4th-instar larvae; light intensity and pH were nonsignificant factors. Rust in the water was also thought to influence distribution towards the surface layer. When 100-400 immatures were released into a full drum, immatures were detected by sweeping and dipping the surface layer on 93.3 and 72.9% of trials, respectively. The correlation coefficients (r) of recoveries of known numbers of immatures by sweeping and dipping varied from 0.92 to 0.98 and from 0.38 to 0.89, respectively. The coefficients of variation were 2-5 times smaller for sweeping than for dipping. Recoveries from dipping were shown to be affected by the water volume in the drum. Counts of 4th-instar larvae from one sweep around the top are sufficient to assess productivity in drums.

Acetyl CoA generation and N-acetylation of serotonin (5HT) in the mosquito, Aedes togoi

Acetyl CoA synthetase (ACS; EC 6.2.1.1) was studied in the mosquito, Aedes togoi, by a novel assay which coupled the acetyl-CoA generated to p-aminosalicylic acid (ASA). The N-acetylated product was determined by an HPLC-fluorimetric procedure. High ACS activity was observed in the newly-pupated pupae of both sexes and in the adult male mosquito whose activity was five times that of the female. Acetyl CoA-dependent N-acetyltransferase (NAT; EC 2.3.1.5) activity toward serotonin (5HT) was also studied using HPLC-electrochemical detection (HPLC-ECD). A progressive increase in the 5HT-NAT activity was observed from the fourth-instar larvae to the adult mosquito with the latter showing 6-fold higher activity in the head compared to the abdomen-thorax region. Kinetic studies on the pupal enzyme extracts showed that the apparent Km values for 5HT and acetyl CoA were 63 and 66 microM respectively. Tryptamine inhibited 5HT-NAT non-competitively with a Ki value of 8 microM.

De novo biosynthesis of juvenile hormone III and I by the accessory glands of the male mosquito

The role of the male accessory glands (MAG) in reproduction was investigated in the mosquito Aedes aegypti. MAG incubated with [14C]acetate synthesized radioactively labeled JH III, JH III bisepoxide and methyl farnesoate. MAG incubated with L-[methyl-3H]methionine synthesized [3H]JH III and a molecule that chromatographed on HPLC with JH I. Analysis of MAG and whole males extract by glass capillary combined gas-chromatography-selected ion monitoring mass spectrometry identified JH III and I as the main analogs that were synthesized by male mosquitoes. MAG of Culex nigripalpus, Anopheles rangeli and Anopheles trinkae also synthesized JH III from L-[methyl-3H]methionine, which indicates that the male mosquito has a complete JH III biosynthetic pathway. Unfed and unmated Culex quinquefasciatus do not develop their ovaries to the resting stage. Females injected with one MAG extract equivalent or implanted with A. aegypti MAG developed their ovaries to the resting previtellogenic stage, whereas females that were injected with saline did not. These results indicate that MAG synthesize and secrete JH III. The corpora allata (CA) of the male Aedes aegypti also synthesize JH III from L-[methyl-3H]methionine. This observation may suggest that JH synthesized by the male's CA is used for internal regulation, whereas JH synthesized by the MAG is transferred with the sperm into the female.

Aedes aegypti lipophorin

The purified lipophorin of Aedes aegypti (Diptera) is composed of two apolipoproteins: apolipophorin I (M(r)=224,000) and apolipophorin II (M(r)=73,000). The density of lipophorin is constant during the Aedes life-cycle and equal to 1.11 +/- 0.01 g/ml. The amount of lipophorin per animal, during the gonotrophic cycles, increases until 48 hr after blood-feeding and then decreases until there is a new blood intake. The density values and quantification of lipophorin during Aedes aegypti gonotrophic cycle suggest that the adaptation to a higher lipid transport demand during oogenesis in Aedes aegypti is accomplished by increasing the amount of lipophorin in the hemolymph. This response is different from that observed in Musca domestica (Diptera) that does not involve changes in hemolymph lipophorin levels.

[A new species of mosquitoes for Guinea Aedes (Aedimorphus) pseudotarsalis van Someren]

The Aedes pseudotarsalis mosquito that is new in Guinea was found in the Middle Guinea (the Fouta-Djallon mountains) in the prefectures of Pita and Kindia in October 1990. The preimaginal phases of this species were collected in the late rainy period in the small temporary water reservoirs (in the erosive hollows), in the axils of herb leaves and in the tanbarks of trees in the vicinities of populated areas.

Cold acclimation, diapause, and geographic origin affect cold hardiness in eggs of Aedes albopictus (Diptera: Culicidae)

Eggs of five strains of Aedes albopictus (Skuse) were obtained in both diapause and nondiapause conditions and exposed to various cold acclimation regimes in the laboratory, after which they were subjected to diverse chilling treatments. Larvae that survived chilling as eggs survived to the pupal stage. Eggs of Aedes aegypti (L.) and Aedes triseriatus (Say) were included as control species. Eggs of temperate Ae. albopictus were more cold-hardy than eggs of Ae. aegypti but less cold-hardy than the eggs of Ae. triseriatus. Cold acclimation and diapause enhanced cold hardiness of only temperate Ae. albopictus. Cold acclimation had a greater influence on cold hardiness than did diapause. Both the temperature and the duration of cold acclimation modulated cold hardiness. Cold hardiness induced in the laboratory was similar to cold hardiness induced in the field in northern Indiana. The cold hardiness of Ae. albopictus from central Florida was intermediate in comparison with temperate and tropical strains. Tropical Brazilian Ae. albopictus and tropical Asian Ae. albopictus were similar in cold hardiness.

Larval diet, adult size, and susceptibility of Aedes aegypti (Diptera: Culicidae) to infection with Ross River virus

The relationship of larval nutrition and adult body size to the susceptibility of Aedes aegypti (L.) to Ross River virus infection was examined. Large adult mosquitoes produced by feeding larvae a high-level diet consumed significantly more virus particles than did smaller mosquitoes. However, when a correction for body size was made, smaller mosquitoes were found to consume significantly more virus per unit of body weight. A host viremia of 2.4 log10 PFU/ml failed to infect mosquitoes of any size. Large Ae. aegypti mosquitoes were significantly more susceptible than small mosquitoes when fed on hosts with viremias of 4.8, 5.7, 6.4, and 7.5 log10 PFU/ml, but differences in susceptibility were less apparent at higher viremias.

[Effect of metallic copper on the larva of Aedes albopictus: 1st laboratory data]

Laboratory experiments were carried out to test the larvicidal properties of metallic copper against Ae albopictus, a species which has spread in Italy during the last 3 years. The results show the strongest lethal effect on 1st stage larvae and support the use of copper as a simple, cheap and environmentally safe agent to control larval breeding of Ae albopictus in peridomestic containers.

Dynamic life table model for Aedes aegypti (Diptera: Culicidae): analysis of the literature and model development

The container-inhabiting mosquito simulation model (CIMSiM) is a weather-driven, dynamic life table simulation model of Aedes aegypti (L.). It is designed to provide a framework for related models of similar mosquitoes which inhibit artificial and natural containers. CIMSiM is an attempt to provide a mechanistic, comprehensive, and dynamic accounting of the multitude of relationships known to play a role in the life history of these mosquitoes. Development rates of eggs, larvae, pupae, and the gonotrophic cycle are based on temperature using an enzyme kinetics approach. Larval weight gain and food depletion are based on the differential equations of Gilpin & McClelland compensated for temperature. Survivals are a function of weather, habitat, and other factors. The heterogeneity of the larval habitat is depicted by modeling the immature cohorts within up to nine different containers, each of which represents an important type of mosquito-producing container in the field. The model provides estimates of the age-specific density of each life stage within a representative 1-ha area. CIMSiM is interactive and runs on IBM-compatible personal computers. The user specifies a region of the world of interest; the model responds with lists of countries and associated cities where historical data on weather, larval habitat, and human densities are available. Each location is tied to an environmental file containing a description of the significant mosquito-producing containers in the area and their characteristics. In addition to weather and environmental information, CIMSiM uses biological files that include species-specific values for each of the parameters used in the model. Within CIMSiM, it is possible to create new environmental and biological files or modify existing ones to allow simulations to be tailored to particular locations or to parameter sensitivity studies. The model also may be used to evaluate any number and combination of standard and novel control methods.

Dynamic life table model for Aedes aegypti (diptera: Culicidae): simulation results and validation

The container-inhabiting mosquito simulation model (CIMSiM) is a weather-driven, dynamic life table simulation model of Aedes aegypti (L.) and similar nondiapausing Aedes mosquitoes that inhabit artificial and natural containers. This paper presents a validation of CIMSiM simulating Ae. aegypti using several independent series of data that were not used in model development. Validation data sets include laboratory work designed to elucidate the role of diet on fecundity and rates of larval development and survival. Comparisons are made with four field studies conducted in Bangkok, Thailand, on seasonal changes in population dynamics and with a field study in New Orleans, LA, on larval habitat. Finally, predicted ovipositional activity of Ae. aegypti in seven cities in the southeastern United States for the period 1981-1985 is compared with a data set developed by the U.S. Public Health Service. On the basis of these comparisons, we believe that, for stated design goals, CIMSiM adequately simulates the population dynamics of Ae. aegypti in response to specific information on weather and immature habitat. We anticipate that it will be useful in simulation studies concerning the development and optimization of control strategies and that, with further field validation, can provide entomological inputs for a dengue virus transmission model.

Protection from ultraviolet irradiation by melanin of mosquitocidal activity of Bacillus thuringiensis var. israelensis

A process for production, isolation, and purification of melanin produced by the fermentation of Streptomyces lividans 66 harboring a recombinant plasmid pIJ702-bearing tyrosinase gene has been developed. The efficacy of melanin in the protection of mosquito larvacidal activity of Bacillus thuringiensis var. israelensis against uv light has been studied. Results obtained by the live cell counts and the bioassay of residual mosquitocidal activity of B. thuringiensis var. israelensis after exposure to uv radiation showed that melanin is an excellent photoprotective agent.

Three simple devices for preventing development of Aedes aegypti larvae in water jars

We developed three types of covers that are easily fabricated from plastic screen locally manufactured in Thailand. The covers were designed to permit normal use of water jars for drinking, utility water uses, and water storage. Tests of the covers in the laboratory and field demonstrated that they could completely prevent successful development of Aedes aegypti (L.) in water jars. Initial experience in a village setting demonstrated that these devices were readily manufactured and used in a community-based program. Village residents adapted the covers to local patterns of water use, collecting rainwater through the screen and adjusting cover use to water depth.

Vector and host relationships of California serogroup viruses in western Siberia

During 1990 and 1991, adult mosquitoes were collected along the Ob River and its tributaries in western Siberia from approximately 51 degrees 18'N to 66 degrees 4'N. Fifteen virus strains were isolated from 74,196 mosquitoes tested in 1,874 pools. These included Tahyna virus from Aedes cataphylla-punctor subgroup (one) and Ae. excrucians (one), and Inkoo (INK) virus from Ae. communis (one), Ae. communis subgroup (one), Ae. hexodontus (two), Ae. punctor subgroup (two), Ae. punctor complex (one), and unidentified Aedes species (three). In addition, a single Ae. euedes yielded a strain of snowshoe hare (SSH) virus and a strain of Getah, an alphavirus. A Bunyamwera serogroup virus was isolated from Ae. excrucians. With the exception of the two isolates from a single mosquito, minimum infection rates among mosquito taxa ranged from 0.4 to 16.7 per 1,000. The INK virus isolates were widely distributed geographically; however, seven of the 10 isolates were from two sites north of the Arctic Circle. During 1991, sera from two mouse species, five vole species, and four shrew species were collected along the upper Ob River for serologic tests. The prevalence of neutralizing antibody to SSH virus in these sera was 80%. Prevalence rates in the four most abundant species were Apodemus agrarius, 73%; Clethrionomys rutilus, 71%; Microtus arvalis, 80%; and Sorex araneus, 91%. This is the first attempt to clarify the vector and vertebrate host relationships of California serogroup viruses in western Siberia.

Habitat overflow, a source of larval mortality for Aedes sierrensis (Diptera: Culicidae)

In laboratory and field tests, larvae of the western tree hole mosquito, Aedes sierrensis (Ludlow), were flushed by rainfall from both glass containers and natural tree holes. After 7 d and an accumulated rainfall of 7.9 cm (3.1 in), between 0 and 327 Ae. sierrensis immatures were recovered in collection devices placed below four natural tree holes. Habitat overflow affected all larval stages and may be an important, but overlooked, density-independent source of larval mortality for mosquitoes developing in some water-filled containers.

Entomologic investigations of an epidemic of St. Louis encephalitis in Pine Bluff, Arkansas, 1991

An epidemic of St. Louis encephalitis (SLE) occurred in Jefferson County, Arkansas during July-August 1991. At least 26 human cases were involved, with 25 cases in the town of Pine Bluff. Twelve isolates of SLE virus were obtained from mosquitoes collected in Pine Bluff between August 13 and 24: 11 from pools of Culex pipiens quinquefasciatus, resulting in a minimum infection rate of 1.6 per 1,000 (n = 6,768) for this subspecies, and one isolate from a pool of 22 mosquitoes identified as Cx. (Culex) spp. Three of the SLE-positive pools, two from Cx. p. quinquefasciatus and one from Cx. (Cux.) spp., also yielded isolates of Flanders virus. Larval surveys resulted in the collection of seven species in four genera from 28 larva-positive habitats and the identification of one significant site of Cx. p. quinquefasciatus production. Ecologic assessments conducted at 12 randomly selected residences resulted in the identification of 17 larva-positive habitats, for an average mosquito-positive habitat rate of 1.4 per residence, and a Cx. p. quinquefasciatus larva-positive habitat rate of 0.6 per residence. Aedes albopictus and Cx. p. quinquefasciatus were the species most frequently encountered in larval surveys in residential neighborhoods.

Anthropophilic mosquitoes and malaria transmission at Edea, Cameroon

An entomological study was carried out during 1990 in the town of Edea in the south of Cameroon to study anthropophilic mosquitoes with special reference to malaria transmission. Man-biting mosquitoes were caught regularly during one night each month in two different districts: Bilalang which is a well planned suburb with 160 houses on a hill-top, provided with a piped water supply; and Pongo which is a densely urbanised suburb in a valley. From 188 man-nights 1030 mosquitoes were collected, comprising 700 Culex quinquefasciatus (68%), 262 Anopheles gambiae (25%) and others species (7%) belonging to the genus Anopheles, Mansonia, Culex and Aedes. The estimated annual biting rates of mosquitoes were 811 bites per man in Bilalang and 2,866 in Pongo. The estimated yearly malaria inoculation rates were 3.8 and 30.2 infective bites per man in Bilalang and Pongo, respectively. In different parts of Pongo district much variation existed; extreme values of the estimated yearly inoculation rate were zero and 86.3 in two houses 200 m apart, located on the top of a hill and in the bottom of a valley, respectively. This study is one of the first conducted on malaria transmission in a moderate sized African town; it shows that the mosquito populations are typically urban and differ greatly from rural ones.

Sustainable urban development and human health: septic tank as a major breeding habitat of mosquito vectors of human diseases in south-eastern Nigeria

Septic tank mosquitoes in Abia State University Okigwe, south-eastern Nigeria were studied using exit traps between November 1988 and April 1989. The results were revealing and striking. Apart from the common septic tank mosquitoes, Culex p. quinquefasciatus, Cu. cinereus and Aedes aegypti, which have been previously commonly found breeding in ammonia and nitrate-rich waters of latrines and septic tanks, the other species, Cu. horridus, Cu. tigripes and Aedes vittatus, have not been commonly reported as colonizing septic tanks in Nigeria. Three out of these six mosquito species observed are vectors of human diseases: Aedes aegypti and Aedes vittatus are vectors of Yellow fever and Cu. p. quinquefasciatus is a potential vector of Bancroftian filariasis and a world-wide vector of various arboviruses. The fact that these mosquito vectors are able to breed in highly polluted waters of septic tanks during the harsh dry months when most surface water bodies are dry is epidemiologically important. The breeding of these mosquito vectors of human diseases around human dwellings indicates an intense man-vector contact creating a high level risk to the crowded urban population. The public health implications of this urbanization/modernization problem and solutions are discussed.

[Extension of the area of Aedes albopictus in Italy. 1st report of the species in central Italy]

A new infestation by Aedes albopictus was discovered in Civitavecchia, Central Italy, in October 1992. This follows previous records of the species in North Italy, where the first infestation was observed in 1990 in the city of Genoa. The present finding clearly indicates the capacity of Aedes albopictus to spread all over Italy and to become a permanent pest in Southern Europe. In spite of the expected embryonic diapause in October, larval breeding was observed in a fifteen-liter glass jar with a narrow neck, left outdoor.

Variation in Aedes aegypti mRNA populations related to strain, sex, and development

Translation products were used to monitor changes in gene expression between different strains and developmental stages of Aedes aegypti. Total RNA was isolated from fourth stadium larvae, male and female pupae, and male and female adults collected at fixed time intervals following pupation and ecdysis. Differences in RNA populations were assessed by in vitro translation followed by one- and two-dimensional polyacrylamide gel electrophoresis and fluorography. Variations in gene expression between sexes and during development were examined in Liverpool (LVP) and Rockefeller (RKF) Ae. aegypti strains. Sex-related differences consisted primarily of differing lengths of expression for certain polypeptides, although two-dimensional electrophoresis revealed changes in intensity of a 44-kD polypeptide with a pI of 7.9 between males and females. Fourth stadium larvae, pupae, and adults expressed different translation products, which probably correlated with developmental differences. Strain-related differences were observed between LVP and RKF.

Influence of temperature on developmental parameters of the parasite/host system Edhazardia aedis (Microsporida: Amblyosporidae) and Aedes aegypti (Diptera: Culicidae)

Larvae of Aedes aegypti, transovarially infected with Edhazardia aedis, were reared between 20 and 36 degrees C to determine the influence of temperature on the development of the parasite and the infected host. Development of the parasite was evaluated based on spore yield and size. The predicted optimum temperature for maximum spore production of E. aedis in A. aegypti was 30.8 degrees C. The results demonstrate that the E. aedis-A. aegypti system has a wide temperature tolerance; whereas spore yield will be lower at unfavorable temperatures, the host will remain infected. Additionally, spores were significantly smaller from individual reared at 34 degrees C than those reared at either 20 or 27 degrees C. Development of the infected host was evaluated based on pupal weight and time of pupation. Infected pupae were significantly larger than uninfected pupae. There was also a significant difference in the pupation rate between controls and infected A. aegypti larvae. Controls had a 50% cumulative pupation time (CPT50) of 65.7 degree days and infected individuals a CPT50 of 76.6 degree days.

First reported outbreak of classical dengue fever at 1,700 meters above sea level in Guerrero State, Mexico, June 1988

An outbreak of classical dengue fever occurred from March to August 1988 in the city of Taxco, Guerrero State, Mexico. Taxco is at an elevation of 1,700 meters above sea level, and this study represents the highest altitude at which an outbreak of dengue has been documented. An investigation was conducted to obtain serologic confirmation of dengue infection, determine the extent of the outbreak, and identify risk factors for dengue illness. Toxorhynchites cell lines were used for viral isolation, and hemagglutination inhibition was used to measure anti-dengue antibody titers. The case definition used in the investigation was any person with fever, headache, myalgias, and arthralgias, or rash or retroocular pain. Dengue virus type 1 was isolated from five acute cases. Of 1,686 persons living in the affected area, 42% (715) met the case definition. Large (200-liter) water containers were significantly associated with infection (relative risk = 1.7, 95% confidence interval 1.5-1.9). The effect of altitude on epidemic transmission is most likely modulated by seasonal temperatures. The epidemiologic and serologic confirmation of a dengue outbreak at 1,700 meters above sea level represents the capability of Aedes aegypti to adapt to new environments, and the potential for epidemic spread in cities at comparable altitudes or higher.

Influence of short time exposure to an insect growth regulator, hexaflumuron, on mortality and adult emergence of vector mosquitoes

Hexaflumuron, an insect growth regulator (IGR), was found to greatly affect the development of immatures and emergence of adults of three species of vector mosquitoes, Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi, when larvae were subjected to short time exposure of < or = 1 h. This IGR could completely prevent adult emergence even at a minimum exposure time of 10 min at 0.001, 0.01 and 0.1 mg/l. On treatment, larval and pupal mortality as well as varying degrees of morphogenetic abnormalities were induced in immatures and adults of the three species. Four weeks of control achieved in a slow moving sullage canal breeding Culex quinquefasciatus indicates that this IGR can be of use in such breeding habitats.

Intradomestic mosquito breeding sources and their management

Seven mosquito species were found to breed in intradomestic breeding sources. An. stephensi and An. subpictus bred in almost all types of containers. Among the culicines, Cx. quinquefasciatus and Ae. aegypti were predominant. Larval breeding was controlled through source reduction or introduction of larvivorous fish Poecilia reticulata. Health education helped in acceptance of the programme by the community. Intradomestic breeding positivity was 2-6% and 16-31% in experimental and control areas respectively.

Adult longevity of certain mosquito species after larval and pupal exposure to sublethal concentration of an insect growth regulator, hexaflumuron

Longevity of the adults of three vector species, Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti was drastically reduced when they were exposed at larval and pupal stages to sublethal concentrations of an insect growth regulator hexaflumuron. When the three species were exposed to 0.05 mg/l at the pupal stage, males and females of Cx. quinquefasciatus suffered a more shortened life span than other species. Among the females whose feeding activity was adversely affected by IGR treatment at the pupal stage, Ae. aegypti showed the minimum survival duration with LT50 of 2.74 days.

Aedes albopictus introduction into continental Africa, 1991

From April 15 through July 20, 1991, an epidemic of yellow fever (YF) occurred in Delta State, Nigeria. In September 1991, as part of a follow-up investigation, mosquito oviposition cups were deployed in four rural communities with YF, all within a 24-kilometer radius of the principal town of Agbor. Based on findings from the follow-up investigation, this report documents the first record of breeding populations of Ae. albopictus--a competent YF virus vector--in continental Africa.

An insular outbreak of dengue fever in a rural south Indian village

In mid 1990, an epidemic of fever affected a single village in Kaniyambadi Block, South India. The illness was characterized by a fever of approximately five days duration, accompanied by headache, chills, sweating and muscle pain. The overall attack rate was 22.5 per cent. The attack rate was uniform across the various age groups and between the sexes. Testing of the acute and convalescent serum samples obtained from cases showed a serological response to dengue virus. The Aedes house index in the village was found to be 36 per cent with toilets serving as active breeding sites. Adjacent villages studied showed similarly high rates of Aedes prevalence, although no cases of the same fever were seen. Since previous exposure to dengue increases the risk for epidemics of dengue hemorrhagic fever and dengue shock syndrome, health education on methods of Aedes control is continuing.

[Biological cycle of Aedes albopictus (Diptera, Culicidae), in the laboratory]

Twelve colonies of Aedes albopictus were maintained at laboratory conditions, with the following results: Insectary conditions--Air humidity: 90-95%; Temperature: 25 degrees C; Blood source: human; Breeding places: Plastic glass or bamboo; Number eggs per female: 36.37; Incubation time: 1 to 6 days; Larval period: 4 to 9 days; Pupal period: 1 to 5 days; Adults life span: females--30.8 days and males--26.6 days.

[Aedes albopictus in Italy and possible diffusion of the species into the Mediterranean area]

Aedes albopictus (Skuse), the important Asian vector mosquito recently introduced in United States and Brazil, is reported from Genoa, North Italy. The infestation was discovered in a kindergarten pre-school center in September 1990 just after the summer holidays. Many discarded tires, well known to provide excellent breeding places for Ae albopictus, had been left in the school playground to be used as toys by the children. After sampling a few biting mosquito specimens for identification, the local health service carried out on September 18 an extensive indoor/outdoor treatment with pyrethroid insecticide. The extent of the infestation in the city of Genoa and in other areas of the Ligurian region has not been evaluated since the identification of the species was available in October, at the end of Ae albopictus reproductive period. A general survey in various Italian regions is being planned for the 1991 spring-summer period. The present record, together with the previous report of Ae albopictus in Albania, clearly supports the hypothesis of a spreading of the species in the Mediterranean area.

Persistence of mosquito-borne viruses in Kern County, California, 1983-1988

The persistence of arboviruses was studied from 1983 to 1988 in mixed agriculture, marsh, riparian, and foothill habitats in Kern County, CA. Western equine encephalomyelitis (WEE) virus was isolated frequently during 1983 from Culex tarsalis and Aedes melanimon and was detected by the seroconversion of sentinel chickens. WEE virus then disappeared, even though vector competence studies during 1984-1986 showed that Cx. tarsalis was able to transmit WEE virus. St. Louis encephalitis (SLE) virus was detected sporadically in 3 of the 6 years of the study by isolation from Cx. tarsalis and/or by sentinel chicken seroconversion. When mosquito pools were screened for virus in suckling mice, Turlock (TUR) and Hart Park (HP) viruses were isolated from Cx. tarsalis during each summer. Vertical transmission of HP was indicated by the isolation of virus from a pool of male Cx. tarsalis. California encephalitis (CE) virus was isolated repeatedly from host-seeking Ae. melanimon females, males, and adults reared from field-collected immatures, verifying vertical transmission in nature. Horizontal transmission of CE virus among both jackrabbits (Lepus californicus) and desert cottontails (Sylvilagus auduboni) appeared to amplify Ae. melanimon infection rates during the summer of 1985, but elevated herd immunity depressed infection rates during 1986. Thus, CE, HP, and TUR viruses persisted in Kern County, while WEE virus appeared to become extinct and required reintroduction. The sporadic occurrence of SLE virus activity remains unexplained, but its persistence may require both vertical transmission and reintroduction.

Temperature-dependent development and survival rates of Culex quinquefasciatus and Aedes aegypti (Diptera: Culicidae)

Development, growth, and survival of Culex quinquefasciatus Say and Aedes aegypti (L.) were determined at six constant temperatures (15, 20, 25, 27, 30, 34 degrees C). The Sharpe & DeMichele four-parameter model with high-temperature inhibition described the temperature-dependent median developmental rates of both mosquito species. In both species, body size generally decreased as temperature increased. Head capsule widths in all instars in both species were significantly greater at 15 than at 30-34 degrees C. Except for the third instar of Ae. aegypti, the larval body lengths in both species were significantly greater at 15 than at 34 degrees C. All instars and pupae of both species and the adults in Cx. quinquefasciatus were significantly heavier at 15 than at 27-34 degrees C. In Cx. quinquefasciatus, survival from eclosion to adult emergence was highest in the range from 20 to 30 degrees C (85-90%) and dropped drastically at 15 (38%) and 34 degrees C (42%). In Ae. aegypti, survival to adult stage was high at 20 (92%) and 27 degrees C (90%) and lowest at 15 degrees C (3%).

Is Aedes albopictus in Australia?

In Brisbane during October 1988 one larva of the exotic dengue vector Aedes albopictus (Skuse) was collected by quarantine officers from a consignment of used vehicle tyres imported from Asia. Although this is not the first report of this mosquito in Australia, the finding was of sufficient importance to change quarantine procedures. Subsequently in Darwin during June 1989, two Ae. albopictus larvae were recovered from an ovitrap located near the wharves. This article reviews the global expansion of this species and, on the basis of previous imports of tyres into Australia, suggests that Ae. albopictus may already be established in this country.

Biosynthesis of mosquito vitellogenin

Vitellogenin (Vg), the hemolymph precursor to the major yolk protein in mosquitoes, is synthesized in the fat body of blood-fed females. Mosquito Vg consists of two subunits with Mr = 200,000 and 66,000. Here, we demonstrate that both the Vg subunits are first synthesized as a single precursor. The identity of this Vg precursor was confirmed by immunoprecipitation with subunit-specific monoclonal antibodies. In cell-free translation of fat body poly (A)+ RNA, the Vg precursor had Mr = 224,000 which increased to 240,000 in the presence of canine pancreatic microsomal membranes. A precursor with Mr = 250,000 was immunoprecipitated in microsomal fractions isolated from rat bodies. With in vitro pulse labeling, the 250-kDa precursor could be detected in homogenates of fat bodies from blood-fed mosquitoes only during the first few hours accumulation of the Vg precursor was achieved by an in vitro stimulation of Vg synthesis in previtellogenic fat bodies cultured with an insect hormone, 20-hydroxyecdysone. The 250-kDa precursor was glycosylated and to a much lesser degree phosphorylated. Treatment of fat bodies with tunicamycin yielded the precursor with Mr = 226,000 which was neither glycosylated nor phosphorylated. The reduction in molecular mass of the 250-kDa Vg precursor and of both mature Vg subunits combined was similar after digestion with endoglycosidase H, indicating that glycosylation is completed prior to cleavage of the Vg precursor. In vitro pulse-chase experiments revealed rapid proteolytic cleavage of the 250-kDa precursor to two polypeptides with Mr = 190,000 and 62,000 which transformed into mature Vg subunits of 200- and 66-kDa as the last step prior to Vg secretion. This last step in Vg processing was inhibited by an ionophore, monensin, and therefore occurred in the Golgi complex. Sulfation as an additional, previously unknown, modification of mosquito Vg was revealed by the incorporation of sodium [35S]sulfate into both Vg subunits. Since sulfation of Vg was predominantly blocked by monensin, the final maturation of Vg subunits in the Golgi complex is, at least in part, due to this modification.

Age dependence of salivary bacteriolytic activity in adult mosquitoes

1. Bacteriolytic activity in the salivary glands of adult Aedes aegypti female mosquitoes starts from a low level upon emergence, increases 6-fold over the first 3 days, then levels off. 2. Mosquitoes start sugar-feeding after 2 days, when lytic activity is one-half of the peak level. 3. Bacteriolytic activity in salivary gland extracts is not influenced by removal of corpora allata.

[The effect of the conditions for the development of Aedes aegypti L. mosquitoes on their infectivity with Plasmodium gallinaceum Brumpt]

Relationship between the conditions of larvae development and mosquito infection with malaria agent was studied. Using the Plasmodium gallinaceum--Aedes aegypti L. model, it was stated that alteration in temperature, number of specimens, and quantity of forage do not change the index of specimen morbidity. Worsening conditions in respect of every one of the enumerated factors lead to a decrease in quantity of agents in carrier.

A decrease in cysteine levels causes the glutathione deficiency of aging in the mosquito

Our previous results indicated that a glutathione (GSH) deficiency is a determinant of the aging process in many tissues and organisms. Correction of this deficiency in the aging mosquito by feeding the cysteine (Cys) precursor magnesium thiazolidine carboxylic acid (MgTc) suggested that the cause could be a lack of Cys. Adult mosquitoes (Aedes aegypti) were fed either a control diet or a diet supplemented with MgTC and then were analyzed for their Cys, cystine, GSH, and glutathione disulfide contents with our HPLC method. The life span profile of Cys levels paralleled that of GSH in the control group with high levels in the young that decreased during maturity and aging. Cystine and glutathione disulfide were undetectable. The causal relationship between the Cys and the GSH deficiencies was shown in the MgTC-supplemented group with an 83% increase in Cys and a 39% increase in GSH relative to control values. Further the conversion steps of MgTC to Cys and then to GSH were verified by use of buthionine sulfoximine. These results demonstrate that a Cys deficiency occurs in the aging mosquito and is the cause of the GSH deficiency.

[Epidemiological research on cases of yellow fever in the northwestern region of the State of São Paulo, Brazil]

Descreve-se investigação epidemiológica conduzida a partir da notificação de três casos suspeitos de febre amarela em moradores da região noroeste do Estado de São Paulo, Brasil, onde se identificou a presença de Aedes aegypti. Concluiu-se que se tratavam de casos de febre amarela silvestre adquirida em área endêmica do Estado vizinho de Mato Grosso. Apesar da presença de focos de Aedes aegypti nos locais de residência dos doentes, não foram encontradas evidências de transmissão do vírus amarílico nesses locais. O teste MAC ELISA mostrou-se de grande utilidade no rápido esclarecimento diagnóstico dos casos suspeitos da moléstia, ao lado das técnicas tradicionais, e no inquérito sorológico conduzido entre familiares, vizinhos e colegas de trabalho dos doentes.

Aedes albopictus in North America: probable introduction in used tires from northern Asia

North American strains of Aedes albopictus, an Asian mosquito recently introduced into the Western Hemisphere, exhibit photoperiodic sensitivity and cold-hardiness characteristics similar to strains originating from temperate zone Asia. Trade statistics for used tire imports, the most likely mode of introduction, also indicate a north Asian origin. Aedes albopictus, an important vector of dengue and a potential vector of many other arboviral diseases, may therefore have the capability of infesting much of temperate North America.

Multiple forms of cerebral peptides with steroidogenic functions in pupal and adult brains of the yellow fever mosquito, Aedes aegypti

In the adult mosquito, Aedes aegypti, the cerebral egg development neurosecretory hormone (EDNH) regulates reproduction by activating the ovaries to synthesize the steroid hormone ecdysone, while during postembryonic development the cerebral prothoracicotropic hormone (PTTH) activates the prothoracic glands to synthesize ecdysone. In each case, ecdysone than drives stage-specific physiological processes. Since EDNH and PTTH share a common steroidogenic function, it is conceivable that they are similar, if not the same, peptide(s). This investigation has begun to address this possibility by determining structural and functional relationships between these two families of neuropeptides. The peptides having EDNH activity in adult and pupal heads of Aedes aegypti were characterized on the basis of their molecular weights and their biological properties in in vitro and in vivo bioassays for EDNH. Gel filtration chromatography of extracts revealed fractions with EDNH activity having molecular weights of approximately 11 kDa and approximately 24 kDa. The similarities in the functional dynamics of these two activities in the different bioassays suggested that comparable moieties existed in pupal and adult brains. The sensitivity of these moieties to proteolytic hydrolysis indicated that they were proteins. Thus at least two EDNH-like peptides appear to be present in pupal and adult heads of Aedes aegypti. The apparent existence of more than one molecular weight form of EDNH has not been reported previously. Since these moieties are present in both pupal and adult heads, it is possible that they have the same steroidogenic function in the two different stages, i.e., to activate ecdysone synthesis, by prothoracic glands in larvae and pupae and by the ovaries in adults.

Sclerotization of mosquito cuticle

The mode of sclerotization of Aedes aegypti pupal and adult cuticle was examined by employing biochemical and radioactive techniques. During larval-pupal metamorphosis, tyrosine is converted to tanning precursors and is incorporated into aryl-amino adducts and beta-crosslinks. The major hydrolysis product of beta-crosslinks in pupal cases is identified to be arterenone. Examination of tanning modes in five different mosquito species shows that the ratio of quinone to beta-sclerotization not only differs within the life stages of the insects, but also differs between species.

Properties of a ribonuclease from Aedes aegypti larvae

1. The properties of a soluble ribonuclease from Aedes aegypti larvae have been compared with ribonuclease activity in adult female tissue. 2. In larval extracts ribonuclease activity was maximal at 40-45 degrees C whereas activity in tissue from adult females was highest at 50 degrees C. 3. Ribonuclease activity that was recovered in a 20-60% ammonium sulfate precipitate was further purified by batch elution from DEAE-Sephacel and from carboxymethylcellulose. 4. Ribonuclease activity in the partially purified fraction was sensitive to EDTA, stimulated by magnesium, had a pH optimum at 9.0 and a Mr of 45,000. 5. Agarose gels containing yeast RNA substrate were used to monitor partial purification of the larval ribonuclease.