Thesis--Wisconsin. / Includes bibliographical references.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 119-122).

Thesis--Wisconsin. / Includes bibliographical references (leaf 85).

Thesis (M.S.)--University of Tennessee, Knoxville, 2003. / Title from title page screen (viewed Sept. 17, 2003). Thesis advisor: Reid R. Gerhardt. Document formatted into pages (viii, 67 p. : ill., maps, charts). Vita. Includes bibliographical references (p. 62-66).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1976. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 81-83).

Southwest Virginia has recently become an emerging focus of activity for La Crosse (LAC) virus, a mosquito-transmitted arbovirus in the California serogroup of Bunyaviruses. In 2005 and 2006, ovitrap surveys were conducted to access the spatiotemporal oviposition activity of LAC virus vectors Aedes triseriatus, Ae. albopictus and Ae. japonicus across a wide region of southwest Virginia. Egg abundance and oviposition patterns of these vectors were significantly different across the three study areas. The primary LAC virus vector, Ae. triseriatus, was collected in the greatest abundance from all three areas, and favored forested habitats. Aedes albopictus was the second most abundant species collected, and was found to favor urban environments. Aedes japonicus also has a preference for urban habitats, and is actively expanding its range throughout southwest Virginia. Dogs were used to determine their efficacy as sentinels for assessing the distribution of LAC virus in southwest Virginia. Canine serum samples were tested using plaque reduction neutralization (PRNT) assays. Of the 436 collected canine serum samples, 21 (4.8%) were positive for LAC virus antibodies. LAC virus seroprevalence was evident in dogs from each study region, including areas where LAC virus human cases and LAC virus positive mosquito isolates have not been reported. As a result, this study provided documentation of horizontal transmission of LAC virus throughout southwest Virginia, demonstrating that dogs make useful sentinels for assessing the distribution of LAC virus in an area. The final objective examined the effects of coinfection with D. immitis microfilariae and LAC virus in three species of Aedes mosquitoes. No significant differences were found between mosquitoes fed dually infected bloodmeals (i.e. D. immitis microfilariae and LAC virus) and those fed bloodmeals containing LAC virus only. A follow-up study found low mosquito midgut penetration rates by D. immitis, despite using biologically significant doses of microfilariae. Failure to demonstrate enhancement of LAC virus in vector mosquitoes suggests that D. immitis does not have a significant impact on LAC virus epidemiology in areas where these organisms co-exist. / Ph. D.

Mosquito surveillance is an integral part of understanding mosquito-borne disease, including and not limited to the La Crosse virus. The primary container-inhabiting Aedeni vectors include Aedes triseritatus, Aedes albopictus, and Aedes japonicus. To better understand the efficacy of gravid traps and oviposition traps as surveillance methods for these mosquitoes, field studies were conducted in three different habitat types. Ae. triseriatus, Ae. albopictus, Ae. japonicus, and Aedes aegypti eggs were described with the aid of color images and SEM. All eggs were broadly cigar shaped with Ae. triseriatus and Ae. japonicus eggs being dull or matte black while Ae. albopictus and Ae. aegypti eggs were shiny jet black. Ae. triseriatus eggs were larger, lighter in color, and have a rougher appearance when compared to Ae. japonicus. Ae. albopictus and Ae. aegypti can be differentiated by the distinct presence of a micropylar collars in Ae. aegypti. Ovitrap and gravid trap efficacy for the surveillance of Ae. triseriatus, Ae. albopictus, and Ae. japonicus were measured in three different habitats on two different sites. Both sites contained the same 2ha habitats with varying degrees of forest canopy disturbance. Ae. triseriatus was the most abundant mosquito on all sites. Ovitraps and gravid traps were efficient in collecting Ae. triseriatus, while ovitraps were not efficient in collecting Ae. japonicus and Ae. albopictus. / Master of Science in Life Sciences

The La Crosse virus (LACV) is an emerging pathogen in the Appalachian region of the United States. The virus maintains a complex natural cycle through horizontal transmission with sciurid rodents and Aedes mosquitoes in Virginia. Transovarial transmission also occurs in this host-parasite system and has evolved for the virus to persist through winter. The virus perpetuates in diapause induced embryos and infects naive rodents the following spring. As global temperatures rise, it is imperative we evaluate how the virus and its vectors overwinter. We conducted experiments to evaluate and determine the diapause induction, or prediapause stage, in Aedes japonicus japonicus, and the ecophysiology and low temperature biology of how LACV affects Aedes triseriatus and Aedes albopictus embryos at low temperatures. We found that the prediapause stage of Ae. j. japonicus is the maternal stage, the developing adult female that lays diapause eggs. This more closely resembles Ae. albopictus and not Ae. triseriatus. As measured in the field and laboratory, LACV has a clear negative effect on the ability of Ae. triseriatus and Ae. albopictus to survive the winter. There was no major effect of LACV infection on the ability of these two species to enter diapause or their critical photoperiods, but there was a significant negative effect of LACV infection on survivorship of embryos that were placed in their natural habitat and in their susceptibility to low temperatures. LACV infection had a more significant negative effect on Ae. albopictus than on Ae. triseriatus and suggests that Ae. albopictus is a subordinate vector relative to Ae. triseriatus in the maintenance of the virus over the winter season. Our findings highlight the need for the increased surveillance of LACV as temperatures continue to rise due to climate change. / PHD / In Virginia, mosquitoes may transmit the La Crosse virus (LACV) that can cause swelling of the brain in humans. This virus infects mosquitoes which is then transmitted to chipmunks. When a mosquito bites an infected chipmunk and then bites a human, the virus be transmitted to the human. Adult female mosquitoes can also pass the virus on to their developing offspring, which is the way it is maintained throughout the winter. Certain infected mosquitoes will spend the winter as eggs and the mosquitoes that hatch carry the virus and can infect chipmunks the following spring. The experiments conducted here looked at how one mosquito that can spread the LACV begins the process to survive the winter. We also did experiments to look at how the virus affects two other mosquito’s ability to begin the same process and then if they can survive the winter and cold temperatures while infected. We found that the Asian Bush Mosquito enters diapause in a different way than we suspected by the female mosquito sensing shorter days at the end of the summer; at this point she will then lay eggs that survive the winter. We discovered that viral infection will hurt the chances of the Asian Tiger Mosquito and Eastern Tree-hole Mosquito to survive the winter. We also found that virus-infected mosquitoes cannot survive temperatures as lower than those that are not infected. This means that the risk of the virus to humans can be greater as temperatures rise due to global warming.

The family Bunyaviridae is the largest of vertebrate diseases and includes the mosquito-borne disease La Crosse (LAC) virus. Vectors include the major vector Aedes triseriatus and two accessory vectors Aedes albopictus and Aedes japonicus. In the past several decades there has been an increase in the number of LAC cases, implication of new vectors, and the appearance of new foci of disease in the southeastern U.S. To better understand the vectors and the relationship between vectors and the virus, laboratory and field studies were conducted to determine oviposition preferences, effect of virus infection on blood-feeding behavior, and compare the efficacy of various methods to determine minimum infection rates of vectors. In laboratory studies of oviposition preference, only Ae. japonicus demonstrated a preference when presented with preexisting eggs. They deposited more eggs in cups containing either conspecifics or Ae. albopictus. The presence of 1st instar larvae Ae. albopictus larvae deterred oviposition by Ae. triseriatus and Ae. japonicus. Ae. japonicus and Ae. triseriatus preferred cups containing larval rearing water (LRW) of conspecifics and Ae. albopictus. Aedes albopictus preferred LRW regardless of species compared to control cups. Field experiments with fresh egg papers and preexisting eggs did not show significant differences, although the unequal population densities of species in the study area confounded the analysis. More work is needed to elucidate the interaction among these species and its effect on oviposition in the field. Blood-feeding experiments showed that LAC virus-infected Ae. triseriatus and Ae. albopictus imbibed significantly less blood compared to uninfected mosquitoes. Because blood meal size affects the subsequent inhibition of host seeking, experiments were done to ascertain the effect of virus infection on refeeding. Significantly more infected Ae. triseriatus mosquitoes refed but there was no effect on the refeeding rate of Ae. albopictus. Thus, the detrimental effect of virus infection, i.e., reduction in blood meal size, may lead to increased host exposure by Ae. triseriatus, enhancing horizontal transmission. Collecting adult mosquitoes was more efficient to detect virus in field populations than the collection of eggs. Maximum likelihood estimation-infection rates (MLE-IR) were calculated using bias-corrected maximum likelihood estimation. Adult collections yielded significantly more positive pools compared with egg collections. Virus was isolated from pools from Ae. canadensis, Ae. triseriatus, and Ae. albopictus. These results are comparable to other studies. / Ph. D.

Recently, the number of human cases of La Crosse encephalitis (LACE), an illness caused by mosquito-borne La Crosse (LAC) virus, has increased in southwestern Virginia, resulting in a need for better understanding of the virus cycle and the biology of its vectors in the region. This project examined the spatial and temporal distributions of the primary vector of LAC virus, Ochlerotatus triseriatus, and a potential secondary vector, Aedes albopictus. Ovitrapping surveys were conducted in 1998 and 1999 to determine distributions and oviposition habitat preferences of the two species in southwestern Virginia. For virus assay, adult mosquitoes were collected at a tire dump and a human case site during 1998 and 1999, and ovitrap samples were taken from a human case site in 2000. In a separate study, a landcover map of Wise County was created by supervised classification of Landsat Enhanced Thematic Mapper imagery, and maps indicating posterior probabilities of high mosquito abundance were created by combining ovitrap survey-derived, landcover-based prior and conditional probabilities for high and low mosquito abundance using remote sensing techniques and Bayesian decision-making rules. Both Oc. triseriatus and Ae. albopictus were collected from all ovitrap sites surveyed in Wise, Scott, and Lee Counties during 1998. Numbers of Oc. triseriatus remained high from late June through late August, while Ae. albopictus numbers increased gradually through June and July, reaching a peak in late August and declining thereafter. Overall, Oc. triseriatus accounted for 90.1% of eggs collected during this period, and Ae. albopictus made up the remaining 9.9%. Abundance of the two species differed among the sites, and in Wise County, relative Ae. albopictus abundance was highest in sites with traps placed in open residential areas. Lowest numbers of both species were found in densely forested areas. Ovitrapping at a human LACE case site during 1998 and 1999 revealed that Aedes albopictus was well-established and overwintering in the area. An oviposition comparison between yard and adjacent forest at the Duncan Gap human LACE case site in 1999 showed that Ae. albopictus preferentially oviposited in the yard surrounding the home over adjacent forested areas, but Oc. triseriatus showed no preference. LAC virus was isolated from 1 larval and 1 adult collection of Oc. triseriatus females from the Duncan Gap human case site, indicating the occurrence of transovarial transmission at this site. The supervised landcover classification for Wise County yielded a landcover map with an overall accuracy of 98% based on comparison of output classification with user-defined ground truth data. Posterior probability maps for Oc. triseriatus and Ae. albopictus abundance reflected seasonal and spatial fluctuations in mosquito abundance with an accuracy of 55-79% for Oc. triseriatus (Kappa=0.00-0.53) and 70-94% for Ae. albopictus (Kappa=0.00-0.49) when model output was compared with results of an ovitrapping survey. Other accuracy measures were also considered, and suggestions were offered for improvement of the model. / Master of Science