Masters Theses

Date of Award

12-2002

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Bonnie Ownley

Committee Members

Carl Jones, William Klingeman

Abstract

Beauveria bassiana (Balsamo) Vuillemin is an entomopathogenic deuteromycete that has been used in biological control of insect pests. Recent studies have revealed that B. bassiana is an endophyte of corn plants, and that plants colonized by the fungus had a reduction in tunneling from the European corn borer, Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae). In addition to corn, B. bassiana has been observed to grow endophytically in potato plants. Beauveria bassiana may also have the ability to colonize closely related plants and potentially reduce insect feeding on them.

This study has three objectives. The first was to evaluate the effect of mycelia from the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae, when incorporated at different rates into a synthetic diet fed to neonate corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) larvae. Larvae fed the highest rates (1 and 5%) of fungal diet experienced delayed development and suffered high mortality. These insects also had lower larval and pupal weights than larvae fed the lower concentrations of mycelia. Insects fed low rates (0.1 and 0.5%) of fungus suffered low mortality and developed at an accelerated rate, compared to fungus free controls, indicating increased nutrition in low rate fungal diets. Insects fed diets containing B. bassiana isolate 11-98 suffered the highest mortality indicating that 11-98 may be more toxic than the other isolates.

In the second study, the effect of Beauveria bassiana was evaluated when metabolites were incorporated at different rates into a synthetic diet and fed to neonate corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) larvae. All larvae fed diets containing metabolites of B. bassiana experienced low mortality, but had delayed development. Those insects fed the highest rate (0.5%) of metabolite-amended diet had significantly lower percent pupation and developed at a slower rate than those insects fed the 0.1% rate.

A third study was designed to establish a technique to detect the presence of endophytic Beauveria bassiana in tomato plants. After seed-treating tomato plants with B. bassiana conidia and allowing them to grow for two weeks in test tubes under gnotobiotic conditions, PCR techniques were used to amplify ITS regions of the plant and fungus from the plant shoot. The presence of B. bassiana in treated plants was confirmed by the PCR amplification of a 550-bp ribosomal RNA gene segment. The amplified product was sequenced using ITS1 and ITS4 primers. The resulting sequence data had 100% homology with a previously published sequence for B. bassiana.

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