Description of the egg of Ochlerotatus japonicus japonicus (Diptera: Culicidae) using variable pressure scanning electron microscopy.

The egg of Ochlerotatus japonicus japonicus (Theobald) is described with the aid of variable pressure scanning electron micrographs. The egg is black, cigar shaped, and tapers ventrally. The length is approximately 591 microm and the width is approximately 172 microm. The outer chorionic cells are irregular in shape, either hexagonal or pentagonal, and decrease in size toward the anterior and posterior poles. Ventral tubercles typically range from three to six and contact the chorionic reticulum. Dorsal tubercles contain two large tubercles with small oval-shaped tubercles grouped around them. A large thread-shaped tubercle extends from this grouping either as a single tubercle or as a series of connected tubercles. The micropylar collar is low and discontinuous and is seldom complete. This description will aid researchers in the identification of this invasive vector species.

The mosquitoes of eastern Tennessee: studies on abundance, habitat preferences, and host-seeking behaviors.

A significant increase in the number of reported cases of La Crosse virus (LACV) infections in eastern Tennessee has occurred in the last ten years. The objective of this study was to determine the abundance and habitat preferences of the potential vectors of LACV in this region. Adult host-seeking mosquitoes were collected using CO(2)-baited CDC light traps and a series of human-landing catches in eastern Tennessee from 2004 to 2006. A total of 4,200 female mosquitoes of 23 species was collected by CO(2)-baited CDC trapping at ten sites during the study period. Aedes albopictus (Skuse) was the most abundant mosquito collected at all sites and vegetation types, with the ratios of total Ae. albopictus to Ae. triseriatus (Say) females collected being 2.1:1 in 2004, 3.8:1 in 2005, and 4.9:1 in 2006. Ten species were collected during a series of human-landing catches made at four different sites; one probable and three confirmed case sites of LACV infections, totaling 528 female mosquitoes. Aedes albopictus was the most abundant species collected, with a 4:1 ratio of Ae. albopictus to Ae. triseriatus females. Aedes albopictus exhibited two clear peaks of "landing" activity, one in the early morning and one in the late afternoon or early evening. Simple and multiple regression analyses of the predictors of the number of mosquitoes collected showed that populations of Ae. albopictus were three times more likely to be collected overall than Ae. triseriatus. Species (Ae. albopictus), vegetation (residential), and the previous cumulative precipitation for the four weeks prior to collection were significantly (P < 0.05) associated with the number of mosquitoes collected by CO(2)-baited CDC trapping. Aedes albopictus was also more likely to be collected than Ae. triseriatus at confirmed cases of LACV infections.

First collection of Ochlerotatus japonicus japonicus in the state of Tennessee.

This is the 1st report of Ochlerotatus japonicus japonicus in the state of Tennessee, USA. Adults were collected at 5 sites in northwestern Knox County from June 9 through November 3, 2003, and from 1 site in both 2003 and 2004.

Temporal abundance, parity, survival rates, and arbovirus isolation of field-collected container-inhabiting mosquitoes in eastern Tennessee.

Surveillance of container-inhabiting mosquitoes was conducted from June 17 through November 9, 1998, at 2 1997 La Crosse virus (LAC) human case sites (Knox and Cocke counties, Tennessee). Mosquitoes were collected weekly with 2 dry ice-baited Centers for Disease Control miniature light traps, 2 omnidirectional Fay traps, and 40 oviposition traps at each site. A total of 8,408 mosquitoes, composed of Ochlerotatus triseriatus (n = 2,095) and Aedes albopictus (n = 6,313), were reared or collected and assayed for virus. The majority of host-seeking Ae. albopictus (n = 567) collected from July through October from both sites were dissected to determine parity status. Monthly parity rates ranged from 0.78 to 0.85 and 0.79 to 0.92 in Knox and Cocke counties, respectively. The high parity rates indicate that this population of Ae. albopictus has a high daily survival rate and may have a high vector potential. The temporal patterns in Ae. albopictus and Oc. triseriatus egg collections from both of the human case sites were significantly correlated, suggesting that the populations fluctuate in a similar manner across the eastern Tennessee region. Although LAC was not isolated from either species, one isolation of a California serogroup virus, most likely a subtype of Jamestown Canyon virus (JC), was recovered from a pool of 50 male Ae. albopictus reared from eggs collected at the Knox County site (minimum field infection rate of 1.89 per 1,000). This is the 1st report of a very closely related JC-like virus in Ae. albopictus and from Tennessee, as well as the 1st time this potential human pathogen has been isolated from transovarially infected field populations of Ae. albopictus.

La Crosse encephalitis in Eastern Tennessee: clinical, environmental, and entomological characteristics from a blinded cohort study.

A blinded cohort study was conducted in 2000 to better understand the emergence of La Crosse virus infection in eastern Tennessee, with special emphasis on the potential mosquito vector(s). Children with suspected central nervous system infection were enrolled at the time of clinical presentation at a large pediatric referral hospital. Clinical, environmental, and entomological data were collected prior to case confirmation. Sixteen of the 40 children included in the final analysis were confirmed to have La Crosse infection by a fourfold increase in antibody titers between collection of acute- and convalescent-phase sera. Factors significantly associated with La Crosse infection included average number of hours per day spent outdoors (5.9 for La Crosse virus cases vs. 4.0 for noncases, p = 0.049); living in a residence with one or more tree holes within 100 m (relative risk = 3.96 vs. no tree holes within 100 m, p = 0.028); and total burden of Aedes albopictus (number of female and male larvae and adults collected at a site), which was more than three times greater around the residences of La Crosse virus cases versus noncases (p = 0.013). Evidence is accumulating that the newly introduced mosquito species Ae. albopictus may be involved in the emergence of La Crosse virus infection in eastern Tennessee.