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Browsing by Author "Wall, Diana, committee member"

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    Characterizing the pine wilt disease pathosystem in the Front Range Region of Colorado
    (Colorado State University. Libraries, 2020) Atkins, David, author; Davis, Seth, advisor; Stewart, Jane, advisor; Wall, Diana, committee member; Tinkham, Wade, committee member
    Pine wilt disease, caused by the pinewood nematode (Bursaphelenchus xylophilus; PWN), is one of the most damaging invasive species in Asia. Tree mortality associated with PWN has recently been reported in Colorado and surrounding states. There remains little documentation on PWN incidence in native pine species or the biology of potential vectors in the Rocky Mountain region. Here we regionally surveyed for PWN in host trees and two putative insect vectors (Monochamus clamator & M. scutellatus) for two years to develop vector flight phenology models and test the hypothesis that disturbance factors predict vector abundance across the landscape. Flight phenology was similar between vectors: flight initiated in mid-July and continued into October for both species. PWN was distributed throughout the Front Range at rates lower than those reported in the putative native range (Host: 3.6%; Vector 4.2%). Infection rate in hosts varied among sites (0-89%), and four 'epicenters' of vector infectivity were identified. We also report the first incidence of PWN-M. clamator association in the U.S. The four identified epicenter sites varied in the timing of anomalous infection frequency, and flight phenology of infective vectors differed between epicenter and peripheral sites. Monochamus populations were found primarily in natural forest areas and seasonally migrate in small numbers to urban areas. Landscape factors such as proximity to burned area were positively correlated with Monochamus abundance. Synthesis and applications: Our study describes PWN infection frequency to be greater than that expected of a newly introduced pathogen, but lesser than the eastern United States and Canada where PWN is known to be established. Our findings provide tools that can predict exposure windows of disease exposure, which were observed to be highest in the early season in Colorado. We also describe the threat that populations of PWN in wildland forests pose to urban landscapes, and how this risk varies seasonally. These findings collectively serve characterize PWN distribution in the native ecosystem and provide tools that can be used by decision-makers and managers to proactively manage the spread of pine wilt disease.
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    The abundance and sources of ice nucleating particles (INPs) within Alaskan ice fog
    (Colorado State University. Libraries, 2024) Lill, Emily, author; Fischer, Emily V., advisor; Creamean, Jessie, advisor; Kreidenweis, Sonia, committee member; Wall, Diana, committee member
    Fairbanks, Alaska often experiences low visibility due to air pollution. Low wind speeds and strong temperature inversions paired with local emissions from burning of wood, oil, gasoline, and coal lead to wintertime pollution events where concentrations of fine particulate matter (PM2.5) often reach 50 μg m-3, exceeding the Environmental Protection Agency (EPA) 24-hour National Ambient Air Quality Standard (NAAQS) of 35 μg m-3. When temperatures fall below -15°C and sufficient moisture is present, these pollution events can facilitate the formation of ice fog, further worsening air quality and visibility issues for aviation and transportation. The formation of ice crystals from supercooled droplets is aided by a small, but critical, number of aerosol particles that potentially act as ice nucleating particles (INPs). However, studies evaluating the quantities and sources of INPs during ice fog are limited. The Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign included the deployment of a suite of atmospheric measurements in January - February 2022 with the goal of better understanding atmospheric processes and pollution under cold and dark conditions. We report on measurements of particle composition, particle size, INP composition, and INP size during an ice fog period (29 January - 3 February). There was a 153% increase in coarse particulate matter (PM10) during the ice fog period, associated with a decrease in air temperature. Results also show a 58% decrease in INPs active at -15°C during the ice fog period, indicating that particles were scavenged by ice fog ice crystals, likely via nucleation. Peroxide and heat treatments were performed on INPs in order to determine the fraction of INPs that were biological, organic, or inorganic. One hypothesis consistent with the results of the peroxide treatments is that more efficient INPs derived from biological materials or organics that typically activate at warmer freezing temperatures may have been depleted during the ice fog event. The reduction in heat-labile INPs during the ice fog event was unexpected for Fairbanks in the winter due to the very low temperatures and limited biological aerosol sources. Aerosol compositional measurements corroborate the presence of INPs from biomass burning and road dust.