Browsing by Subject "Soybean aphid"

Now showing 1 - 4 of 4
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    Economic Aspects of Crop Pest Management and Monarch Conservation
    (2020-08) Thakur, Tiesta
    The dramatic rise in prophylactic chemical treatments for pest and weed control in the past two decades have raised many environmental concerns. Although cost effective, such treatments which include neonicotinoids and herbicide tolerant (HT) crops contaminate soil and water and cause wildlife habitat loss. In my thesis, I explore the economics of eco-friendly practices of the farmers ranging from bio-diversity conservation to adapting integrated pest management. In the first chapter, I survey Midwestern farmers to estimate their willingness to grow milkweed on their non-cropland for Monarch butterfly conservation for various remuneration rates. I also approximate intrinsic motivation of farmers from their actual conservation data using reverse regression, distance discriminant analysis and control functions to test for motivation crowding out. Findings indicate motivation crowding out at modest levels of compensation. Alternatively, high remuneration crowds in farmers motivation to conserve Monarchs. The second chapter estimate soybean farmers' value of information provided by alternative configurations of a monitoring network for soybean rust (Phakopsora pachyrhizi). It shows that a network of 400 sentinel plots can maximize the expected profit of soybean farmers provided more plots are placed in the Corn Belt where the risk of soybean rust infection is lower, but where much more soybean is produced in contrast to the current spatial arrangement where sentinel plots are disproportionately placed in the Southern US. The last chapter examines the economic suitability of Unmanned Aerial Vehicles (UAVs) for scouting soybean aphids (Aphis glycines Matsumura) based on a plant-level spatiotemporal bioeconomic model of infestation. Findings indicate that the optimal profit from UAV based scouting is equivalent to that from manual scouting. But its greater tendency to detect false positives can also trigger frequent unnecessary treatments and dramatically reduce farmers' profits. Yet, UAV's commercial viability depends more on reducing its operating cost than improving its precision, once it has a tally threshold of 250 soybean aphids per plant.
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    The effects of rainstorms on soybean aphids, Aphis glycines (Matsumura)
    (2014-03) Krueger, Caitlin Colleen
    Soybean aphid, Aphis glycines (Matsumura), is a significant economic pest of soybean in North America. Three experiments were conducted to determine the influence of abiotic factors on aphid populations and distribution on soybean plant canopies. Aphids were exposed to rainfall simulations in field and in greenhouse settings while resident populations were observed before and after rainstorm events. Aphis glycines population changes were influenced most greatly by sample period and a sample period*treatment interaction during in-field rainfall simulation. Shifts in population distribution were significantly influenced by sample period and interactions between sample period and location of the plot, canopy level and treatment. Visual comparisons before and after trials indicated that small dips in population and random shifts in canopy population distribution quickly returned to original levels after the application of rainfall. An in-field aphid observational study indicated that some abiotic factors associated with rainstorm events are conditionally significant. Average wind speed, the interaction between maximum observed wind speed and rainfall, average aphid starting population and location/soil type of the observed field significantly affected aphid population. Sample period and pre-count averages were found to be significant to aphid distribution on the plant canopy.
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    Functional response and the effects of insecticidal seed treatment on the soybean aphid parasitoid, Binodoxys communis
    (2013-08) Carter, Megan Elizabeth
    The soybean aphid, Aphis glycines, is native to Eastern Asia where populations are regulated, in part, by natural enemies such as the braconid parasitoid wasp Binodoxys communis. However, the establishment of B. communis in North America as a classical biological control agent where A. glycines populations have reached economic injury levels, has been unsuccessful to date. This study examined the impact of neonicotinoid seed treatment on B. communis, as well as determined the parasitoid's functional response. Seed treatments and biological control are often both used in a soybean aphid integrated pest management (IPM) regime. A field study was conducted to evaluate any impact seed treatment may have on the parasitoid. There were eight susceptible soybean plots, four of which were untreated and four were treated with a neonicotinoid seed treatment. Adult male and female wasps were released onto individual caged plants and mummies were collected 10 days later. Proportion of aphids that mummified, emergence rates, sex ratios, and hind tibia lengths of the offspring were measured as fitness parameters of the parasitoid and compared between treatments. The results suggest that even though there was an effect on B. communis fitness, the results may not be biologically significant due to inconsistent results across all parameters in the study. Another potential hypothesis for the parasitoid's difficulty as a classical biological control agents, could be a type IV (or `domed') functional response, i.e., increased parasitism per capita with increased host density to a threshold level, beyond which the parasitism per capita decreases. The functional response of B. communis on A. glycines was measured at six aphid densities, ranging from 10 to 1000 per soybean plant. Aphids were placed on plants two days prior to exposure to a single, mated, one-day-old female B. communis. The parasitoid was left on the plant for 24 hours and 10 days later all mummies were collected. Emergence rates, sex ratios, and hind tibia lengths of the offspring were measured as fitness parameters of the parasitoid. The results of this experiment were consistent with a type IV functional response. Parasitism per capita by Binodoxys communis increased with number of aphids per plant and decreased between 500 and 1000 per plant. This may indicate a limit to this parasitoid's ability to control A. glycines populations during outbreaks. Furthermore, the more that is known about parasitoid ecology, the easier it will be to forecast successful establishment of future agents.
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    Source, Fall-Winter 2009
    (University of Minnesota Extension, 2009) University of Minnesota Extension