Theses and Dissertations at Montana State University (MSU)

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    Olfactory preference and reproductive isolation of two Mecinus species (Coleoptera: curculionidae): implications for biological control of dalmatian, yellow, and hybrid populations of Toadflax, Linaria species
    (Montana State University - Bozeman, College of Agriculture, 2016) Hubbard, Charles Eli; Chairperson, Graduate Committee: David Weaver
    Classical biological control of the exotic, invasive toadflaxes Linaria vulgaris (L.) Mill. and Linaria dalmatica Mill. has had both successes and failures. One of the new challenges land managers face is the apparent increase in vigor shown by naturally occurring hybrid populations of the two toadflax species. This has presented practical problems because managers now are unable to decide which weevil species to use on these hybrids: Mecinus janthinus, which is found on L. vulgaris, or M. janthiniformis which has preference for L. dalmatica. This key question was addressed using olfactometer experiments to determine if the volatile profile for each plant establishes host fidelity for the naturally-occurring associated Mecinus species. Adults of both insect species were paired in cages on clones of naturally occurring and synthetic reciprocal cross hybrids and the parent toadflax species to quantify mating events and to determine the number of offspring produced on clones of each plant type of plant in incomplete randomized blocks. We did this using both intraspecific and interspecific pairs of Mecinus species to determine how many offspring are produced by intraspecific adults and also to explore the possibility of establishing a hybrid weevil population using clones of each plant type. Host plant preference for both Mecinus species is influenced by olfactory responses, but this was only evident for adult females. Our first series of no-choice experiments with intraspecific mating pairs indicated that M. janthiniformis is more successful in terms of offspring produced for all types of hybrid toadflax tested. The results also showed that M. janthinus had a higher percentage of survival on all types of hybrids. As expected each Mecinus species performed best on its natural host plant. The results of our second series of no-choice experiments suggest that these two weevil species can produce viable interspecific offspring on clones of most of the plant types evaluated. This suggests that the newly described M. janthiniformis is very similar to M. janthinus and the separation between the two species is controlled at least in part, by olfactory cues from the favored host. In the future, land managers can better decide which Mecinus species to use based on whether the hybrid weed species is influenced more by L. vulgaris, or L. dalmatica.
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    Effects of Brachypterolus pulicarius on growth and seed production of Dalmation toadflax
    (Montana State University - Bozeman, College of Agriculture, 1998) Grubb, Robert Thomas
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    Determination of host races in three insect species attacking Dalmatian toadflax and yellow toadflax in North America
    (Montana State University - Bozeman, College of Agriculture, 1991) McDermott, Gregory James
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    Genetic and behavioral variability in the ovary-feeding Nitidulid Brachypterolus pulicarius collected from Dalmatian and yellow toadflax
    (Montana State University - Bozeman, College of Agriculture, 2002) Hering, Kelly Lynn; Chairperson, Graduate Committee: David K. Weaver
    Braychypteroluspulicarius is an ovary-feeding beetle in the family Nitidulidae. The species is found on Dalmatian and yellow toadflax, two non-native, invasive weeds. The beetle is native to Eurasia and is considered an important natural enemy and biological control agent for toadflax. Because B. pulicarius is found, at varying densities, on both yellow toadflax and Dalmatian toadflax, questions have been raised about the potential existence of host races in the species. Amplified fragment length polymorphism (AFLP) molecular genetic techniques are commonly used in studies of population genetics. Because it is a relatively easy and reliable method that does not require previous knowledge about the beetles’ genome, the AFLP technique was utilized to examine the patterns of variability of populations ofB. pulicarius. Patterns of observed variability that corresponded with commonality of host plant could serve as evidence for host races in B. pulicarius. Insects were collected from both yellow and Dalmatian toadflax at a total of 12 locations in the northwestern US, British Columbia, and Europe. Volatile collections were made from host plants to characterize their chemical emissions and to look for species-specific plant differences. Behavioral assays were attempted to determine if beetles showed a preference for the species of host plant from which they were collected. Volatile collections revealed variability in volatile production within and between host plant species. Behavioral trials were highly variable and preference results were not obtained. AFLP analyses revealed variation that did not correspond to host plant commonality. Overall, the study revealed the dynamic nature and a high level of uncertainty surrounding the fundamental knowledge of this biological system. No evidence was found for host race existence in B. pulicarius. Alternative explanations for the observed variabilities are discussed.
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    Invasiveness of Yellow Toadflax (Linaria Vulgaris) resulting from disturbance and environmental conditions
    (Montana State University - Bozeman, College of Agriculture, 2008) Lehnhoff, Erik Adam; Chairperson, Graduate Committee: Lisa J. Rew; Bruce D. Maxwell (co-chair)
    Invasive plant species are considered to be one of the greatest threats to ecosystems and biological diversity throughout the world, and are thus often aggressively managed. The degree of plant invasiveness, however, varies both with environment and with type of landscape disturbance. This research was designed to understand how the factors of environment and disturbance affect the invasiveness of Linaria vulgaris (yellow toadflax) in southwest Montana and to quantify the varying degrees of invasiveness resulting from each factor. Data were obtained through four separate projects. The effects of disturbance size and propagule pressure on L. vulgaris establishment were evaluated through a series of experiments in both disturbed and undisturbed plots. L. vulgaris establishment and survival were low in all plots, but followed the general trend of more successful establishment in larger disturbed plots and in disturbed plots with a higher seeding density. An invasiveness index was developed that quantified invasiveness between -4 and +4 based on changes in population density and plant occupancy within permanent monitoring grids. This index was applied to L. vulgaris populations in three distinct environments, and invasiveness was found to range from -1.9 (declining population) to 1.8 (invasive population), indicating that invasiveness varied widely based on environment. The effects of the disturbances of herbicide, digging, burning and vegetation clipping on established L. vulgaris populations were evaluated in four environments. In the first year after treatment, herbicide reduced invasiveness of L. vulgaris in all environments, while digging and burning increased invasiveness and clipping had no effect. In the second year, herbicide resulted in increased L. vulgaris invasiveness at the three sites dominated by forbs, while it still reduced invasiveness at the grass-dominated site. The other treatments had minimal effects. Finally, effects of the above disturbances on the whole plant community were assessed using relative species abundance, richness and diversity metrics. Treatments generally decreased these metrics initially, but values recovered over time, with the exception of the herbicide treatment. The results demonstrated that L. vulgaris population invasiveness and treatment effectiveness varies with environment, suggesting that prioritizing management on an environment basis may be appropriate.
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    Toadflax, fire, Mecinus janthinus, and compensatory growth
    (Montana State University - Bozeman, College of Agriculture, 2005) Anthony, Antoinette; Chairperson, Graduate Committee: Theodore Weaver.
    Dalmatian toadflax is a noxious weed of the western United States. In western Montana it invades in the foothills zone where bunchgrasses (Agropyron spicatum and Festuca idahoensis) meet low forests (Pinus ponderosa and Pseudosuga menziesii). Our results show that wildfire strengthens toadflax, probably at the expense of native grasses. The stem boring weevil, Mecinus janthinus, is being tested as the most likely biocontrol agent for the weed. On our toadflax infested sites in the Agropyron spicatum/Pinus ponderosa zone Mecinus established, survived, and spread slowly (2-4m/yr) for two years following introduction. At the low initial densities Mecinus induced compensatory growth in toadflax i.e. stem density, plant height, branch number, and seed capsule number all increased. In a garden experiment, we exposed plants to Mecinus at increasingly higher densities (0-32 insects per plant) to measure the effect of a higher attack rate. With exposure rates of 2-4 insects per plant compensatory growth occurred. With exposure rates greater than 8 insects per plant total biomass and especially flower biomasses were reduced. If Mecinus densities in the field exceed eight weevils per plant this may indicate eventual exhaustion and decline of the weed.
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    The impacts of a stem boring weevil, Mecinus janthinus, on dalmatian toadflax, Linaria dalmatica
    (Montana State University - Bozeman, College of Agriculture, 2008) Schat, Marjolein; Chairperson, Graduate Committee: Robert K. D. Peterson; Fabian D. Menalled (co-chair)
    Classical biological control of weeds is generally considered an effective, safe, and cost effective tool for controlling widespread weeds in natural areas. However, only 60% of releases have become established and, of those, only 50% have led to control. Therefore, understanding the impacts of agents on target weeds across spatial scales, at different insect densities, and over time can give biological control practitioners the knowledge necessary to improve establishment and success rates. My studies characterized the impacts the biological control agent, Mecinus janthinus, on the rangeland weed Dalmatian toadflax (Linaria dalmatica) at individual plant and plant population scales. Individual plant studies were conducted in a garden and replicated on plants growing in the field, to measure the impact of agents on plant growth and primary physiology. The population study followed operational scale releases of M. janthinus for three to four years using intensive monitoring to characterize L. dalmatica cover, density, and population structure, and weevil establishment and population increase. I also evaluated which parameters were most important to measure to determine establishment and success. In the common garden experiment, M. janthinus injury was found to reduce relative plant growth, as well as root, stem, and reproductive biomass at medium and high adult densities. Trends of reduced photosynthetic, conductance, or transpiration rates with increasing M. janthinus density were observed. In the field experiment, M. janthinus injury led to reduced growth. Gas exchange rates decreased over the season and were lower in plants exposed to high larval and adult herbivore pressure. Field monitoring indicated successful M. janthinus establishment at releases across a range of elevations, slopes, and geographic locations, though high rates of overwintering mortality were observed at all sites. Linaria dalmatica cover was variable within watersheds and patches, and also differed between watersheds. Abundance of L. dalmatica decreased over time based on cover measurements, but did not change over time with respect to density. The proportion of mature L. dalmatica stems decreased over time. The majority of changes in L. dalmatica over time were the same in release and control transects and could not be attributed to M. janthinus.
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