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

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Larvae of Ae. triseriatus mosquitoes were collected from treeholes on the Ball State University campus. These insects were raised to adulthood under laboratory conditions. Newly hatched larvae were raised in deionized water. One hundred twenty-five of instar 1 mosquitoes (group A) were placed into separate baby food jars containing deionized water. These jars were separated into five groups. The pH of the water in each group was adjusted to 3, 4, 5, 6 and 7 with a 70% to 30% sulfuric-nitric acid solution. Subsequent groups consisting of instar 2, 3 and 4 larvae and pupae (groups B, C, D and E respectively) were exposed to the same experimental treatment as that of group A. The effects of each of these pH levels on mortality and development was observed until the insects reached maturity or died.Larvae in water of pH 3 experienced a higher percentage of mortality than mosquitoes exposed to less acidic solutions. A decrease in mortality with age was observed. Mortality of insects in group A was greater than that of any other group. Mosquitoes in group D experienced the lowest mortality.Variations of developmental time for mosquitoes in pH 3 were probably due to high mortality. Developmental time was similar for all groups. Slight variations between these groups may have been due to natural fluctuations in development. The total average developmental time for Ae. triseriatus mosquitoes of this study was 11.12 days.

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The influence of forest canopy disturbance (FCD) on La Crosse virus (LACV), leading cause of US pediatric arboviral encephalitis, is critical to understand in landscapes where forests are periodically harvested. Southwestern Virginia is part of an emerging focus of this interior forest bunyavirus. I investigated how the temperate forest mosquito community, LACV vectors, and the LACV amplifying vertebrate host (chipmunks) were impacted by logging. This research was conducted across an experimental FCD gradient (from least to most disturbed: contiguous control, fragmented control, clearcut, and high-leave shelterwood (SW)). Using gravid traps, I found that the mosquito community was resilient to logging with no significant difference in diversity or community composition across treatments. Mean number of female mosquitoes caught per trap-night declined with disturbance. FCD significantly affected the abundance of vector species in different ways. The primary LACV vector, Aedes triseriatus, and the recent invasive Ae. japonicus declined with logging. Other vectors (Ae. albopictus, Ae. canadensis, and Ae. vexans) thrived with logging. Culex pipiens/restuans was affected by disturbance but had no treatment preference. A mark-recapture study revealed that chipmunk abundance and LACV seroprevalence were greatest on the SW. In sync with Ae. triseriatus abundance but in contrast to the chipmunk results, mosquito LACV detection was significantly greater on unlogged sites. Surprisingly, LACV was detected in Ae. japonicus and Cx. pipiens/restuans. In a follow-up study, I isolated LACV from field-collected Ae. japonicus. Although LACV was previously isolated from Cx. pipiens, the vector competence was unknown. Therefore, I examined the vector competence of Cx. pipiens and Cx. restuans. Although poor vectors, I did detect LACV in the saliva of both species. An additional experiment found that nutritionally-stressed Cx. restuans were better vectors than those in the control group, indicating that environmental stressors (e.g., FCD) may alter the ability of accessory vectors to spread LACV. The influence of FCD on LACV is complex. Because logging decreases Ae. triseriatus abundance, human LACV risk is likely lowered by decreased transovarial vertical transmission. However, high chipmunk seroprevalence on disturbed sites suggest horizontal transmission with accessory vectors plays a larger role in LACV risk on recently logged sites. / Ph. D.

Zika (ZIKV), La Crosse (LACV), and Cache Valley (CVV) viruses are mosquito-vectored diseases that cause significant morbidity and mortality in humans and animals. Transmission of these viruses are dependent on numerous factors including vector competence and the effects of mosquito-virus interactions. We conducted vector competence studies of local Aedes and Culex mosquitoes for ZIKV and CVV, and found that all Aedes mosquitoes were competent for CVV and only Aedes albopictus and Aedes japonicus were competent for ZIKV. Vector competence for CVV was dose-dependent, where mosquitoes orally infected with high titers developed higher transmission rates. We also found that vector competence for ZIKV was limited by midgut and salivary gland barriers. Second, we looked at the effects of LACV and ZIKV infection on repellent response in Aedes mosquitoes and found that infected mosquitoes were refractory to low concentrations of DEET, picaridin, and PMD. Increasing concentrations of the repellents to ≥10% was able to increase percent protection (%p) against infected and uninfected mosquitoes. Lastly, we determined the effects of ZIKV and LACV infection on oxidative stress and glutathione-S-transferase (GST) activity in Aedes albopictus. Virus infection had no effect on oxidative stress, but GST activity was significantly different for mosquitoes 3-days post-exposure. We found that oxidative stress levels and GST activity had an inverse relationship for infected and uninfected mosquitoes, where oxidative stress decreased and GST activity increased over the 10-day test period. This indicates that GSTs may aid in controlling byproducts of oxidative stress. The results from this entire study identified competent vectors for emerging arboviruses and demonstrated the behavioral and physiological effects of virus infection in the mosquito vector. / Doctor of Philosophy / Zika (ZIKV), La Crosse (LACV), and Cache Valley (CVV) viruses are transmitted by mosquitoes and can make humans and animals very sick. There are many biological factors that determine if a mosquito can transmit a virus and these viruses can change the biology of a mosquito. We conducted laboratory studies to see if Aedes and Culex mosquitoes can transmit ZIKV and CVV. We found that all Aedes mosquitoes were able to transmit CVV and only the Asian tiger mosquito and Asian rock pool mosquito were able to transmit ZIKV. Mosquitoes infected with high amounts of CVV developed higher transmission rates. We also found that transmission of ZIKV was limited by barriers in the mosquito midgut and salivary glands. Second, we looked at the effects of LACV and ZIKV infection on how Aedes mosquitoes respond to repellents and found that infected mosquitoes were less sensitive to low concentrations of DEET, picaridin, and PMD. Increasing concentrations of the repellents to 10% or higher was able to provide adequate protection against infected and uninfected mosquitoes. Lastly, we determined the effects of ZIKV and LACV infection on oxidative stress and glutathione-S-transferase (GST) activity in the Asian tiger mosquito. Virus infection did not change oxidative stress, but GST activity was higher in infected mosquitoes tested after 3 days after infection. We found that oxidative stress decreased and GST activity increased over the 10-day test period. This indicates that GSTs may help control damaging products from oxidative stress. The results from this entire study identified what mosquitoes were able to transmit emerging mosquito-borne viruses and demonstrated the biological effects of virus infection in the mosquitoes.