Masters Theses

Date of Award

5-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Reid R. Gerhardt

Committee Members

Carl J. Jones, Arnold M. Saxton

Abstract

West Nile Virus (WNV) was reported as present in ShelbyCountyin 2001 with 44 blue jays testing positive for WNV. The first reported human WNV case had an onset date of 27 July 2002. There were 40 human cases in 2002, six of which were fatal. The 2002 human cases were clustered within the I-240 beltway, the older residential area of greater ShelbyCounty. Adult mosquito collections were made from the first week in June through the first week in November for 2003 and 2004. A representative site was selected from both the high and low human WNV incidence area of ShelbyCounty, and mosquito populations surveyed using CDC light-traps, omni-directional Fay traps, gravid traps, and by aspiration of natural and artificial resting stations. Collection data for 2004 reported here are only through 6 October. There were significantly higher numbers of Aedes vexans, Anopheles quadrimaculatus, and Ochlerotatus triseriatus collected in the low human WNV incidence area and higher numbers collected of Culex pipiens collected in the high incidence area in a site by species comparison (P= 0.0025). Total number of mosquitoes collected did not differ between sites (P= 0.36). 2003 Memphis Botanic Gardens (MBG) gravid trap data were compared with collection data from 26 Shelby County Vector Control (SCVC) gravid trap sites. There were differences between 2003 surveillance sites overall (P< 0.0001) with MBG sites having lower numbers of Cx. pipiens than any SCVC site. However, the two sites were not statistically different. Rainfall was found to play a significant role in weekly collection totals (P= 0.0089), as was average weekly temperature (P < 0.0001). This varied for individual years indicating that climatalogical effects cannot be assessed based on one year’s data.

Blood-fed mosquitoes were collected from Shelby County, Tennessee in 2003 and 2004 using backpack and handheld battery-powered aspirators in addition to gravid traps. Only three of the collected species, Aedes vexans, Culex pipiens, and Ochlerotatus triseriatus, have been processed to identify blood-meal host. Combined trapping methods produced 399 engorged female mosquitoes. Of the 53 female mosquitoes tested, 33 Cx. pipiens, 18 Ae. vexans, and two Oc. triseriatus, hosts for 32 of those were positively identified using a polymerase chain reaction method, which utilized avian and mammalian specific oligoneucleotide pimers designed from conserved portions of the large mitochondrial ribosomal subunit gene (16S). The results for Cx. pipiens analyzed thus far varied by collection season with winter collections (N=9) being 100% avian (2 of 2 identified) and summer collections (N=24) being 94% mammalian (15 of 16 identified).

Adult female mosquitoes previously identified to species were dissected and parity determined. Approximately 40 individuals per month

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