Document Type

Thesis - University Access Only

Award Date

1995

Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

Abstract

Laboratory and field studies were conducted to determine the effects of Beauveria bassiana (Bals.) Vuillemin on non-target arthropods and target grasshoppers. In the laboratory, a spraytower was used to simulate the aerial application of treatments on migratory grasshoppers, Melanoplus sanguinipes (Fab.), yellow mealworms, Tenebrio molitor L. and alfalfa leafcutting bees, Megachi/e rotundata (Fab.). Spray treatments included air (control), 0.9 ml of oil, and 2.64 x 109 B. bassiana conidia in 0.9 ml of oil. A total of 3 60 individuals from each species were tested. The experiments consisted of four replications arranged in a Completely Random Design. Grasshoppers and alfalfa leaf cutting bees were extremely susceptible to B. bassiana infection. After ten days, grasshopper mortality was 73%, and alfalfa leaf cutting bee mortality was 88%. Yellow mealworm mortality in B. bassiana treatments was very low, and the pathogen did not appear to affect these insects. Large scale field studies were conducted on rangeland near Amidon, North Dakota in 1993. Treatments included aerially applied B. bassiana and carbaryl (an industry standard for grasshopper control). Pitfall and malaise traps were utilized to monitor noniv target arthropod populations. Ring counts were used to estimate grasshopper densities in test plots. There was unusually high amounts of precipitation following treatments, and grasshopper densities declined in control, B. bassiana, and carbaryl plots. Analysis of grasshoppers from control plots revealed that environmental conditions had been favorable for a natural outbreak of B. bassiana. The inundative release of laboratory reared B. bassiana conidia appeared to produce an additive effect. Grasshopper densities in B. bassiana plots were reduced by 53%. Carbary} provided excellent grasshopper control. Grasshopper densities were reduced by 93% post-treatment. Important ground-dwelling arthropods collected from in pitfall traps included spiders (Araneae), ants (Formicidae) and ground beetles (Carabidae). Abundance of ground-dwelling arthropods decreased slightly in all plots following treatments, but rebounded shortly after. An observed short term decline in ground-dwelling arthropod activity may have been associated with increased precipitation. Abundance of aerial insects increased in all plots following treatments. Overall results indicate that non-target arthropods were not significantly impacted by B. bassiana or carbaryl treatments.

Library of Congress Subject Headings

Grasshoppers -- Biological control Pathogenic fungi Arthropoda -- Pathogens

Format

application/pdf

Number of Pages

144

Publisher

South Dakota State University

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