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In 1920, Culex coronator was reported from San Benito, Texas, and later in Arizona, New Mexico, and Oklahoma. In 2005, this species was reported to be spreading across the southeastern USA. Now reported in 14 states, it has been found as far north as northern Oklahoma; Memphis, TN; and Suffolk, VA. The public health significance of Cx. coronator is not firmly established, even though it has been implicated as a potential vector of several arboviral diseases. This study aims to document additional Cx. coronator county-level records, to provide information about its continued expansion across the southern USA, and to provide a short research update into its vector potential. Data acquired through multistate collaborations and author collections resulted in 146 new county records from Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, and Texas. No new county records were presented for Arizona, New Mexico, Tennessee, or Virginia, which had previously reported this species. With these new data, this species has been documented in 386 counties in 14 states of the continental USA., (Copyright © 2021 by The American Mosquito Control Association, Inc.)

Aedes aegypti has reappeared in urban communities in the southwestern U.S.A. in the 1990s after a 40-year absence. In 2003 and 2004, a systematic survey was conducted throughout metropolitan Tucson, AZ, to identify human and environmental factors associated with Ae. aegypti distribution within an arid urban area. Aedes aegypti presence and abundance were measured monthly using the Centers for Disease Control and Prevention enhanced oviposition traps at sampling sites established in a grid at 3- to 4-km intervals across the city. Sampling occurred in the summer rainy season (July through September), the peak of mosquito activity in the region. Multiple regression analyses were conducted to determine relationships between mosquito density and factors that could influence mosquito distribution. House age was the only factor that showed a consistent significant association with Ae. aegypti abundance in both years: older houses had more mosquito eggs. This is the 1st study of Ae. aegypti distribution at a local level to identify house age as an explanatory factor independent of other human demographic factors. Further research into the reasons why mosquitoes were more abundant around older homes may help inform and refine future vector surveillance and control efforts in the event of a dengue outbreak in the region.

Aedes aegypti, the mosquito responsible for transmitting dengue, has colonized many cities and towns throughout Arizona. Determining both the migration between, and the origin of, local Ae. aegypti populations is important for vector control and disease prevention purposes. Amplified fragment length polymorphism was used to infer geographic structure and local substructure, and effective migration rates (M, migrants per generation) between populations, and to determine genetic differentiation between populations (PhiPT). Three geographically and genetically differentiated groups of populations were identified. Population substructure was only detected in the border town of Nogales. Reliable estimates of M between regions ranged from 1.02 to 3.41 and between cities within regions from 1.66 to 4.44. In general, pairwise PhiPT were lowest between cities within regions. The observed patterns of genetic differentiation suggest infrequent migration between populations and are compatible with the idea of human transport facilitating dispersal between regions.

Oviposition traps were used to follow changes in the population of Aedes aegypti (L.) (Diptera:Culicidae) in a seven-block area in midtown region of Tucson, Arizona. About 20,000 eggs were collected over a period from 1 June to 14 October 2000. Peak mosquito populations were correlated with the late summer rains. Mosquitoes seeking a blood meal were collected and dissected to determine if they had previously fed, i.e. if they were parous. Of the 241 females examined, 44% were parous, with a range from 0% to 80%. Females that had blood in their guts were collected and the source of blood was identified using an ELISA. Preliminary results suggest that 80% of them had fed on humans. These data suggest that the reproductive history of Tucson populations of Ae. aegypti could be conducive for transmission of dengue viruses.

Background: Oocyte development was studied in the autogenous black fly, Simulium vittatum (Diptera, Nematocera), a vector of Onchocerca volvulus, the causative agent of onchocerciasis., Results: Oocyte growth was nearly linear between adult eclosion and was complete by 72 hours at 21 degrees C. The oocyte became opaque at 14 hours after eclosion indicating the initiation of protein yolk deposition. The accumulation of vitellogenin was measured using SDS-PAGE. The density of the yolk protein bands at about 200 and 65 kDa increased during the first and second days after eclosion. The amount of protein in the 200 kDa band of vitellogenin, determined using densitometry, rapidly increased between 12 and 25 hours after eclosion. Ecdysteroid levels were measured using a competitive ELISA. Ecdysteroid levels increased rapidly and subsequently declined during the first day after eclosion., Conclusion: These data show a correlation between the appearance of vitellogenin in the oocyte, and the rise in ecdysteroids. A possible relationship to molting of the nematode, Onchocerca volvulus, is discussed.

Historically, malaria was a significant cause of morbidity and mortality throughout the western United States, and Anopheles freeborni Aitken was thought to be the vector west of the Continental Divide. In 1989, Anopheles hermsi Barr & Guptavanij was described and subsequently found to be an effective laboratory vector of Plasmodium. The adults of these two species are morphologically indistinguishable, and therefore polymerase chain reaction was used to analyze the DNA from 48 mosquitoes collected in Arizona and Colorado (identified morphologically as An. freeborni). All specimens were identified as An. hermsi. This was the first report of An. hermsi in Arizona and Colorado and indicated that this Anopheles species historically may have been a malaria vector in these two western states.

Vesicular stomatitis is an economically important arboviral disease of livestock. Viremia is absent in infected mammalian hosts, and the mechanism by which insects become infected with the causative agents, vesicular stomatitis viruses, remains unknown. Because infected and noninfected insects potentially feed on the same host in nature, infected and noninfected black flies were allowed to feed on the same host. Viremia was not detected in the host after infection by a black fly bite, but because noninfected black flies acquired the virus while co-feeding on the same host with infected black flies, it is concluded that a viremic host is not necessary for an insect to be infected with the virus. Thus co-feeding is a mechanism of infection for an insect-transmitted virus.

In previous experiments we have demonstrated that colonized and wild black flies are competent laboratory vectors of different Mexican and Western USA isolates of vesicular stomatitis virus, serotype New Jersey (VSV-NJ). We have recently demonstrated biological VSV-NJ transmission by black flies using animal models. In the study described here, we tested the vector competence of colonized and wild black flies for the vesicular stomatitis virus, serotype Indiana (VSV-IN). A 1998 equine isolate was used. After a 10 day incubation period, saliva from experimentally infected Simulium vittatum and S. notatum was individually collected and tested for the presence of infectious virus. Virus was detected in the saliva of both species following oral infection, indicating that they are competent laboratory vectors of VSV-IN. In addition, the results suggest that the black fly gut may exert evolutionary pressures on the virus.

Laboratory-reared female black flies (Simulium vittatum Zetterstedt) were infected experimentally with a 1997 vesicular stomatitis virus New Jersey serotype isolate and allowed to feed on susceptible laboratory mice. All mice exposed to black fly bite seroconverted by day 21 after infection, an indication of virus transmission. In addition, viral RNA was detected in the spleen of several mice. These findings are consistent with the hypothesis that black flies are involved in VSV-NJ transmission during epizootics in the western USA and represent the 1st confirmed example of biological transmission of an arbovirus by a member of the Simuliidae using an animal model.

Anticoagulant activity was determined in salivary gland extracts from four species of black flies, i.e., Simulium vittatum Zetterstedt, Simulium argus Williston, Simulium metallicum Bellardi, and Simulium ochraceum Walker. Inhibition of coagulation factor Xa occurred among all four, whereas thrombin inhibition was detected in S. argus and S. vittatum only. Both bovine and human alpha-thrombins were inhibited with the highest activity occurring with S. argus salivary gland extracts. Factor Xa inhibition was highest in S. ochraceum, an anthropophilic species and vector of Onchocerca volvulus, and lowest in S. vittatum, a primiparous autogenous species that is also zoophilic. Total soluble salivary gland extract protein also varied among the four species with the highest concentration measured in S. ochraceum and the lowest in S. vittatum. A positive correlation was observed between the amount of soluble protein and percentage of inhibition of factor Xa for the four species.

The salivary gland activities of apyrase, an enzyme that prevents platelet aggregation by eliminating ADP, were compared among five members of the Anopheles gambiae species complex and An. albimanus. Within the An. gambiae group, An. quadriannulatus exhibited the lowest amount of enzyme activity at all pH levels measured. Apyrase activity could be separated into three groups at pH 7.5 and 8.0. The two most anthropophilic species (An. gambiae and An. arabiensis) exhibited higher activity at pH 9.0. Anopheles merus and An. melas, both saltwater taxa, and An. albimanus, a New World species, exhibited peak apyrase activity at pH 8.0. When the effects of divalent cations (Ca++, Mg++) on enzyme activity were compared at pH 8.5, apyrase activity in the presence of Mg++ could be separated into three levels. Anopheles gambiae and An. quadriannulatus exhibited reduced activity in the presence of Mg++. Anopheles arabiensis, An. merus, and An. melas displayed the highest relative levels of activity. Anopheles albimanus, with a Mg:Ca ratio of 0.80, was most similar to An. arabiensis. These biochemical differences suggest that different isoenzymes of apyrase have developed within the genus Anopheles.

The humoral antibody responses to salivary antigens of Simulium vittatum Zetterstedt were investigated in a BALB/c mouse laboratory model. Production of antisera was stimulated by intraperitoneal immunization with salivary gland extract or by feeding flies directly on depilated mice. Antibody responses in these two groups of mice were compared by western blotting, thus characterizing "true" salivary immunogens present in salivary gland extract. Immunized mice developed IgG, IgM, and IgE antibodies which recognized several salivary gland components, ranging in molecular weight between 26 and 67 kDa. Sera from bitten mice recognized fewer antigens, indicating that some components of the salivary gland extract were poorly immunogenic or absent from the saliva secreted during blood feeding. Antisera raised against S. vittatum also were used to identify cross-reactive immunogens and allergens in salivary gland extracts from other New World simuliids (Simulium argus Williston, S. metallicum Bellardi, and S. ochraceum Walker). SDS-PAGE protein profiles indicated a high degree of similarity between salivary gland extract of S. vittatum and S. argus, and several cross-reacting antigens were identified by western blotting. In contrast, protein profiles of S. ochraceum and S. metallicum differed from the former species, both qualitatively and quantitatively. Antisera demonstrated a low degree of cross-reactivity against salivary gland extract of S. ochraceum, whereas no cross-reactivity was detected against S. metallicum. These observations were confirmed using a monoclonal antibody raised against S. vittatum salivary gland extract (designated SVSG.1.F10), which showed cross-reactivity against S. argus but failed to recognize salivary gland components of either S. ochraceum or S. metallicum.

Simulium vittatum females were shown to be competent vectors for the New Jersey serotype (VSNJ) of vesicular stomatitis virus (Camp Verde strain). Seventy percent of females infected intrathoracically transmitted infectious virions in their saliva after a 10-d incubation period. When infected with virus per os, 63% of the flies tested were positive at day 10, and 45% of flies infected in this manner also secreted virus in their saliva by day 9 or 10 after infection. When ingested by S. vittatum females, VSNJ virus readily replicated and increased from a mean baseline titer of 1.2 x 10(4) pfu per fly to 3 x 10(4) pfu per fly on day 10. An eclipse phase was demonstrated between approximately 18 and 48 h postinfection. This experimental evidence supports the hypothesis that black flies play a major role in the epizootic transmission of VSNJ. This is also the first confirmed example of biological transmission of an arbovirus by a member of the Simuliidae.