Date of Award
Master of Science
Entomopathogenic fungi (EPF) kill pests and can diminish outbreaks. Species of EPF such as Beauveria bassiana and Metarhizium brunneum (formerly M. anisopliae) are significant mortality factors for several insects. Better understanding of these organisms is an essential step in developing strategies to conserve EPF in agricultural systems. We hypothesize that 1) organically farmed soil is more suitable to EPF than conventional soil, and 2) conventionally-farmed soil, coupled with the use of synthetic chemical inputs, could have negative impacts on EPF. In 2011 and 2012, soil was collected from organic and conventional fields of corn and soybean and the field margins. Entomopathogenic fungi from the soil samples were quantified by measuring mortality of larval greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae), and by counting colony-forming units on selective growth media. Field history and soil properties were analyzed with multiple regression analysis to determine factors that may affect the abundance of fungal EPF. In 2011, the EPF B. bassiana and EPF in the genus Metarhizium were lowest in conventional fields, and the average number of colony-forming units for Metarhizium spp. was also lowest in conventional fields. Multiple regression analysis revealed that abundance of Metarhizium was positively associated with applications of organic fertilizer and silt content, and negatively associated with nitrogen content, tillage, conventional field margins, conventional fields and herbicide applications. A laboratory study was conducted in which herbicides and fungicides were applied to soil containing different strains of Metarhizium, and the abundance of fungi was measured after the addition of pesticide by quantifying colony-forming units on selective media and larval mortality of G. mellonella. None of the pesticides had significantly negative impacts on the abundance and virulence of Metarhizium spp. These results suggest that soil properties and particular farming practices, can affect populations of soil-borne EPF.
Eric Harold Clifton
Clifton, Eric Harold, "Impacts of conventional and organic agriculture on soil-borne entomopathogenic fungi" (2013). Graduate Theses and Dissertations. 13370.