An important variable in determining the vectorial capacity of mosquito species for arthropod-borne infections is the degree of contact of the vector and the vertebrate reservoir. This parameter can be estimated by examining the host-feeding habits of vectors. Serological and polymerase chain reaction based methods have been used to study the host-feedings patterns of 21 mosquito species from New York, New Jersey, and Tennessee, 19 of which previously have been found infected with West Nile virus. Mammalophilic mosquito species in New Jersey and New York fed primarily upon whitetailed deer, while those from Memphis, Tennessee, fed mainly upon domestic dogs. A total of 24 different avian host species were detected among the avian-derived blood meals. American Robin, Northern Cardinal, Northern Mockingbird, Tufted Titmouse, and Brown-headed Cowbird were common avian hosts, while blood meals derived from the American Crow were relatively rare. Although the majority of common host species were potentially among the most abundant birds at each location, the proportion of blood meals from the most commonly fed upon avian species was greater than was predicted based upon the likely abundance of these species alone. These findings suggest that vector species for West Nile virus may preferentially feed upon certain avian hosts.

Introduction of potential disease vectors into a new geographic area poses health risks to local human, livestock, and wildlife populations. It is therefore important to gain understanding of the dynamics of these invasions, in particular its sources, modes of spread after the introduction, and vectorial potential. We studied the population genetics of Aedes (Finlaya) japonicus japonicus (Theobald), an Asian mosquito that was recognized for the first time in the United States in 1998. We examined patterns of genetic diversity using random amplified polymorphic DNA and sequences of ND4 of mtDNA by comparing samples from populations spanning the range of this mosquito in Japan (six samples) and the United States (nine samples) as well as specimens intercepted in New Zealand in 1999. We found geographically differentiated populations in Japan, indicating limited gene flow even on small spatial scales. In the United States, we found evidence of significant genetic differentiation between samples from New York, Connecticut, and New Jersey and those from mid-Pennsylvania and Maryland. We were unable to pinpoint the source location(s) in Japan, although some of the U.S. samples are genetically close to samples from south Honshu and western Kyushu. Further studies should include samples from Korean populations. Distinct genetic signatures in U.S. populations undergoing expansion suggest the possibility of local increases in genetic diversity if and where they meet.

Eastern equine encephalomyelitis virus (EEEV) is perpetuated in eastern North America in a mosquito-wild bird maintenance cycle that involves Culiseta melanura (Coquillett) as the principal enzootic vector and passerine birds as the primary amplifying hosts. We examined the role of birds in the EEEV cycle at a site in southern New Jersey where EEEV cycles annually at high levels. Birds and mosquitoes were sampled during three epiornitics and one season of limited virus activity. We examined antibody prevalence in birds in relation to eight physical and natural history characteristics. Our goal was to compare EEEV cycling in C. melanura and the primary avian hosts better to understand the mechanisms that initiate annual epiornitics. Antibody prevalence was highest in the Blue Jay (62%), Wood Thrush (60%), and Tufted Titmouse (44%). Resident status of birds was the natural history characteristic most closely linked to participation in the EEEV cycle. Species spending the greatest amount of time at our study site (permanent residents, summer residents) had the highest antibody rates. We captured viremic birds as early as 25 May, 51 d before we first detected virus in C. melanura. We recaptured 10 after hatching year adults and one hatching year (HY) bird that seroconverted before we detected virus in C. melanura. We also found EEEV antibody in 15 HY birds up to 31 d before we isolated EEEV from C. melanura. We provide evidence that a cryptic cycle develops weeks before epiornitic cycling is detected in C. melanura by traditional laboratory techniques, indicating that the early season cycle is initiated by the recrudescence of latent virus in previously infected birds.

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We describe methodology used for the laboratory colonization of Aedes japonicus japonicus, an exotic mosquito species native to eastern Asia and first collected in New Jersey as larvae in 1999. We created a free mating colony in 2000 that readily bloodfed on restrained bobwhite quail (Colinus virginianus). A larval diet of finely ground Purina Lab Diet dissolved in dechlorinated water has proven acceptable. This is the first report of Ae. j. japonicus colonization from mosquitoes collected in the United States.