MITPPC Research publications

Persistent link for this collectionhttps://hdl.handle.net/11299/241449

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Browsing MITPPC Research publications by Type "Thesis or Dissertation"

Now showing 1 - 3 of 3
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    Distribution and Traits of the Fungal Pathogen Fusarium virguliforme that Influence Spread and Survival in Minnesota
    (2021-08) Hall, Rebecca
    Fusarium virguliforme is an invasive fungal pathogen responsible for soybean sudden death syndrome (SDS) and root rot of other legumes. Despite a previous study that suggested the pathogen would not survive in Minnesota due to winter cold stress, the pathogen was found in southern Minnesota in 2002 and has continued to spread throughout the state since its discovery. While much has been learned about the SDS pathogen in the United States, more work is needed to better understand the distribution of F. virguliforme in soybean and other crop fields and the strategies the pathogen uses to survive and spread in northern climates. This thesis includes studies of key traits that may aid in the survival of F. virguliforme, including 1) the asymptomatic and symptomatic host range of this fungus in a field setting, 2) the cold temperature limits of the pathogen’s survival, and 3) the unique nutrient use profiles of F. virguliforme. This work sought to expand our knowledge of the distribution of the pathogen within Minnesota. A distribution study in soybean fields was conducted in 2018 and 2019 based on SDS symptoms and the use of a specific qPCR assay. SDS and F. virguliforme were confirmed for the first time in Rice, Isanti, and Stevens counties; and the pathogen was confirmed for the first time in Clay, Douglas, Hubbard, and Pope counties. Cold temperature limits of the pathogen that may influence the spread and survival of F. virguliforme in Minnesota’s current and future climate were explored. It was determined that the pathogen can survive to temperatures of -40°C and thus survival is not likely limited by cold temperatures in Minnesota. The host range of the pathogen was studied to define which plant species may be vulnerable to disease development and potentially help the survival of F. virguliforme. Eleven species of dry edible beans, native legumes, prairie grasses, and prairie flowers common in the Midwestern United States were selected for field and greenhouse studies. It was determined that black bean, pinto bean, kidney bean, and pea are symptomatic hosts, whereas alfalfa, showy tick trefoil, black-eyed Susan, Indiangrass, partridge pea, and white clover are asymptomatic hosts. Lastly, the nutrients that support the growth of F. virguliforme, as well as the relative nutrient preferences and competitive abilities of F. virguliforme compared to other fungal and oomycete species commonly found in soil or soybean roots was explored within this thesis. The results suggest that F. virguliforme utilizes a larger number of carbon and nitrogen sources, both of which are potentially released from germinating seeds and crop residue and are strong stimulants of F. virguliforme growth. Additionally, it was determined that F. virguliforme is more competitive for these nutrients than the other species included in this study.
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    Improving Stink Bug Management in The Midwest: Understanding Dispersal Capacity and Developing Sampling Plans
    (2020-12) Carlesso Aita, Rafael
    Stink bugs are an emerging threat for horticultural and field crops in the North Central Region of the United States. This threat can be attributed to the increase in abundance of Pentatomidae species native to North America over the years, and to the spread of invasive stink bugs throughout this region, in particular, the brown marmorated stink bug, (Halyomorpha halys). There is a lack of decision-making frameworks that provide more efficient sampling for stink bugs in soybean for this region, and there is a need to understand the dispersal capacities of laboratory-reared H. halys. Therefore, my research developed more efficient sampling for herbivorous stink bugs in this region and assessed the dispersal capacity of H. halys under laboratory conditions. First, I developed a binomial or decision-making sequential sampling plan for herbivorous stink bugs by using data from 11 states of the North Central Region. Results showed that using a tally threshold of 3 stink bugs per 25 sweeps for action thresholds corresponding to the current action thresholds of 5 (soybean grown for seeds) and 10 (soybean grown for grain) stink bugs per 25 sweeps, provided the best sampling outcomes in terms of efficiency and accuracy. In addition, we showed that 18 and 12 sample units, for action thresholds of 5 and 10 stink bugs per 25 sweeps respectively, would be needed for reliable decision-making sampling. The development of a binomial sequential sampling plan for stink bugs in soybean should provide increased efficiency with regards to the number of sample units required to reach a management decision. Secondly, I assessed the effects of starvation, age, mating status, and pre-flight weight on flight parameters of laboratory-reared H. halys using flight mills. Although some statistical differences were observed across the experiments, these differences represented minimum ecological significance. These results could reflect the resilience of H. halys as a successive invasive species to North America and could help predict the dispersal potential of this species in Minnesota. The results of my thesis will provide valuable information to fine-tune integrated pest management strategies for stink bugs in the North Central Region, enabling more efficient scouting for growers and consultants as well as better forecasting the dispersal capacity of an important invasive species to the region.
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    Population Ecology Of Aphelinus Certus, An Adventive Parasitoid Of Soybean Aphid In North America, With Implications For Biological Control
    (2020-05) Miksanek, James
    Parasitoids are excellent model systems in addressing fundamental aspects of biology and ecology while offering a high degree of economic and ecological value in regulating the population densities of their host species in both natural and agroecological settings. The single most important arthropod pest of soybean is the soybean aphid (Aphis glycines). Although not recommended for release due to its broad host range, the parasitoid Aphelinus certus has since been accidentally introduced into North America and has been hypothesized to be a key natural enemy of soybean aphid. However, the overall impact of A. certus in the biological control of soybean aphid is uncertain. The chapters in this thesis are united by broader theories and concepts addressing the role of A. certus in biological control. Chapter 1 presents a coupled-equations matrix population model parameterized by a series of laboratory bioassays outlining the life history of soybean aphid and A. certus; analysis of the model suggested that a parasitism rate of 0.21 d−1, which would be equivalent to at least 3.4% mummies, is capable of maintaining soybean aphid below economically damaging levels in 31.0% of simulations. Chapter 2 further explores the effects of host density on parasitoid lifespan and reproduction as well as establishes a quantitative wing wear index for estimating the age of field-collected parasitoids. Moving from theoretical to in-field efficacy, Chapter 3 evaluates the impact of A. certus on soybean aphid in soybean fields across central and western Minnesota (United States) from 2017–2019; contrary to the predictions of the model in Chapter 1, the results of this field experiment did not find a strong effect of A. certus in reducing the population growth rates of soybean aphid. Finally, Chapter 4 evaluates the prevalence of parasitism by A. certus on the native aphid species Aphis asclepiadis and Aphis monardae in prairie ecosystems; these results suggest that A. certus readily colonizes or is already established in natural habitats and poses a potential threat to endemic aphid populations. Lastly, I offer conclusions by more broadly discussing this work within the context of population dynamics, ecology, and biological control.