Masters Theses

Date of Award

12-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Reid R. Gerhardt

Committee Members

Roberto M. Pereira, John New Jr.

Abstract

Mosquito surveillance in 1998 and 1999 was conducted in an eleven-county region in eastern Tennessee to determine the regional fauna and investigate disease vectoring potential of container-inhabiting species. The eastern Tennessee region has experienced an increase in the number of human cases of La Crosse (LAC) encephalitis since 1996. The virus is endemic in western North Carolina and the etiological agent of human disease since the early 1980's. Due to the recent increase in eastern Tennessee cases, the virus is suspected of reaching a new endemic focus in the Appalachian region. The introduction of an exotic species, Aedes albopictus, that is capable of transmitting the virus under laboratory conditions, may play a role in virus transmission in eastern Tennessee mosquito populations.

Weekly surveillance of Ae. triseriatus and Ae. albopictus was conducted from June through November, 1998 at two 1997 LAC virus human case sites in Knox and Cocke Counties, Tennessee. Adult females of both species were collected weekly in host-seeking COj-baited Centers for Disease Control (CDC) miniature light traps and dissected to determine parity status. Aedes albopictus females were collected in sufficient numbers to make inferences about the female population and high parity rates were found (Knox 77- 80%, Cocke 80-92%) indicating high survivability and potentially high vector competence.

Although the Knox and Cocke County sites were located approximately 82 km apart, the seasonal patterns of egg collections from both species were significantly correlated suggesting that populations fluctuate in a similar manner across the region. The lU eggs of both species collected in oviposition traps were reared to the adult stage and tested for viruses by the CDC. Although, the rearing success of the eggs was minimal, 8,408 mosquitoes (Ae. triseriatus n=2,095, Ae. albopictus n=6,313) were reared for virus isolation and a pool of male Ae. albopictus was positive for Jamestown Canyon (JC) virus (MIR=0.16/1,000). This is the first time JC has been isolated from transovarially infected field populations of Ae. albopictus and the first documentation of the virus in mosquitoes collected in Tennessee.

Surveillance of the mosquito fauna from ten collection sites in ten counties was done bi-weekly from May-October, 1998 and April-July, 1999. The known LAC virus vector, Ae. triseriatus, and suspected vector, Ae. albopictus, are well-distributed in the region constituting 60% of adult mosquitoes collected in 1998 and 47% in 1999. These collection sites will be surveyed during future seasons to develop baseline data of mosquito species in the region. Adult Ae. albopictus were collected in larger numbers than Ae. triseriatus while the oviposition traps collected Ae. triseriatus eggs far more readily than Ae. albopictus eggs. For this reason, adult trap collections do not give a good indication of the population in the majority of habitats. One exception is habitat with numerous artificial containers (trash and tire dumps), where host-seeking traps collected numerous adults, while, due to the competition of larval sites, the oviposition activity in ovitraps was extremely low.

Each of the collections sites was located in the vicinity of Tennessee Valley Authority (TVA) reservoir and few adult Anopheles species (>5%) were collected during both years. The public mosquito complaints are likely not the result of species produced in TVA lakes and waters, since the majority of species collected were container-inhabiting mosquitoes, and few lake-inhabiting species.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS