Browsing by Subject "Biological control"

Now showing 1 - 5 of 5
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    Biological Control of Canada Thistle in Wetland Prairie Restoration
    (Minnesota Department of Transportation, 2007-10) Eichstaedt, Kari; Wyse, Donald; Johnson, Gregg
    Pseudomonas syringae pv. tagetis (Pst), a phytopathogenic bacterium, was evaluated as natural biological control agent for Canada thistle [Cirsium arvense (L.) Scop.]. Canada thistle patches exhibiting symptoms of Pst infection commonly occur along roadsides in association with perennial grasses and a grass litter layer. Field experiments were conducted to determine if grass and litter provide an environment that supports Pst infection of Canada thistle or if grass, litter, and soil collected from infected Canada thistle patches act as inoculum sources for Pst infection of Canada thistle. This experiment provides evidence that grass and litter are important components of the landscape that support the natural Pst infection of Canada thistle, and perennial grass competition has potential to manage Canada thistle in roadside rights-of-way and wetland restoration sites. A previously published Pst specific primer set was determined to require high Pst populations for detection.
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    Effects of human actions on four ecological systems, with a focus on trophic relationships
    (2013-12) Kosmala, Margaret Candace
    There are, perhaps, no parts of earth remaining that haven't been impacted by human actions, either purposefully or unintentionally. Agriculture and livestock grazing occupy much of earth's arable land, oceans are overfished, greenhouse gas emissions are changing the climate, and human transportation has facilitated unintentional invasions of organisms. In order to become better stewards of Earth's biota, we must better understand how our actions - both direct and indirect - affect ecosystems and species. I examine four ecological systems and the direct and indirect effects of human change on them, with a focus on trophic (eating) relationships. First, I analyze the environmental impact of beef production, especially in the U.S., which has the most industrialized system in the world. Next, I present the results of an experiment testing the effects of plant diversity on the biological control of an agricultural pest species. An invasive species, the soybean aphid, has become a major pest of soybean in the U.S. in the past fifteen years, and efforts to control the aphid with natural enemies could reduce the need for pesticides. Third, I analyze a twenty-year seed addition experiment to investigate the long-term dynamics of plant communities. The results highlight the importance of dispersal limitation combined with local competition and movement of species over time. Finally, I describe a model that captures the dynamics of an emerging wildlife disease: bovine tuberculosis in lions in Kruger National Park, South Africa. The modeling results reveal the most likely long-term effects of the disease in this lion population and efficacy of intervention approaches.
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    Flight capacity of emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) and its parasitoid Tetrastichus planipennisi (Hymenoptera: Eulophidae), in response to several experimental treatments
    (2014-12) Fahrner, Samuel Joseph
    Emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive beetle native to eastern Asia. Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) is one of three hymenopteran parasitoids currently being introduced into North America as part of a classical biological control program against emerald ash borer. Here, custom-built, computer-monitored flight mills were used to measure the effects of age, feeding status, mating status, sex, and size on flight metrics of T. planipennisi. The flight mill was then used to measure flight metrics of emerald ash borer and T. planipennisi across a range of temperatures and relative humidity. The relationship between flight energetics, specifically flight distance, with temperature was then integrated with landscape temperatures at ten locations throughout the continental United States to compare relative dispersal capacity for emerald ash borer and T. planipennisi. The goal of this research was to elucidate factors that mediate the flight capacity of both insects and, for T. planipennisi, to infer the pre- and post-release conditions that may optimize flight capacity.
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    Invasive plants, herbivores and the underground: feedbacks with soil biota and their influence on grassland plant communities in the Great Plains
    (2013-04) Haines, Dustin F.
    Exotic plants have the ability to modify soil seed banks and the soil biotic community in habitats they invade, but little is known about the legacy of invasion once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following control of spurge: a return of native plants, or a secondary invasion of other exotic plants. Furthermore, reduced native plant recruitment has been observed in areas where insect biocontrol has been used for leafy spurge control. It is unknown, however, if the reduced recovery of natives is due to a depauperate native plant seed bank, altered soil biotic communities, or interactions of leafy spurge with biocontrol organisms. To address the seed bank question, I monitored soil seed banks and standing vegetation for two years in mixed-grass prairies that were previously invaded by leafy spurge. I found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community. I conducted a glasshouse experiment to investigate interactive effects of leafy spurge soil conditioning and flea beetle biocontrol insects on native plants. My results indicate that leafy spurge soil conditioning inhibits native plant germination and growth, and that flea beetles have similar inhibitory effects but only on particular native plant species. Lastly, I investigated the interactive effects of leafy spurge root exudates and fungal pathogens on native plant growth in a glasshouse, and the degree to which fungal pathogen growth varies with leafy spurge and native plant root exudates in petri dishes. I found that leafy spurge root exudates and fungal pathogens, when applied together, tended to enhance native plant germination and growth, and that fungal pathogen growth response to root exudates varied between fungal genera, and among native species, but that fungal growth did not respond strongly to leafy spurge exudates. Therefore, regardless of the relatively unaltered native plant seed banks, leafy spurge soil occupancy and fungal pathogens may have significant impacts on native plant recovery.
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    Mind the Gap: the evolution of oviposition site and specialisation in the parasitoid superfamily Chalcidoidea
    (2018-03-05) Boulton, Rebecca A; Heimpel, George E; rebeccaboulton87@googlemail.com; Boulton, Rebecca A
    Parasitoid wasps have contributed significantly to our understanding of ecological specialisation and the evolution of traits linked to host range. Oviposition site is one such trait. Endoparasitoids deposit their eggs inside the host body and tend to be more highly specialised than ectoparasitoids (which lay eggs externally) because they must develop specific strategies to overcome host immune defences. Intermediate to endo- and ectoparasitism is a strategy that we call ‘gap laying’. Gap-laying parasitoids deposit their eggs between the hard outer puparium and the larva of dipteran hosts. This behaviour has received less empirical attention than endo- and ectoparasitism but has important implications for the evolution of specialisation. Using a phylogenetically controlled comparative approach we find that gap-laying species in the hymenopteran superfamily Chalcidoidea exhibit numeric host ranges intermediate to endo- and ectoparasitoids, but these groups exploit a similarly taxonomically related range of hosts. We found that gap-laying can arise from ectoparasitism or endoparasitism, but once it evolves it shows patterns consistent with an evolutionary dead-end compared to other strategies. The results of this study demonstrate how oviposition site, beyond the normal endo-ectoparasitoid dichotomy, influences host specificity, shedding light on the causes and consequences of ecological specialisation in the parasitic Hymenoptera.