Semester of Graduation

Fall 2023

Degree

Master of Science (MS)

Department

Entomology

Document Type

Thesis

Abstract

In the United States, control of the sweetpotato weevil [SPW, Cylas formicarius elegantulus (Summers)] occurs through quarantine and regular use of chemical insecticides. However, an overreliance on chemical control may lead to resistance. Entomopathogenic fungi have potential to act as an alternative to chemical control. In this study, we assessed four different strains of Metarhizium isolated from soil collected in Louisiana (Mp-K048, Ma-K056, Mr-K082, and Mr-K101) and compared them to a well-known licensed strain (Mb-ARSEF 1095) for virulence against C. formicarius elegantulus. Results suggested that Mp-K048, Ma-K056, and Mr-K082 had the best hazard ratios. Overall, Mp-K048 was the most effective Metarhizium sp. tested with a hazard ratio of 8.85, a median lethal time of 4 days, and the lowest median lethal concentration of 2.6 * 105 spores/ml. However, when Mp-K048 and Ma-K056 were tested with other bioinsecticides (Entrust and neem oil), there was no significant difference in median lethal time, although the hazard ratio differed significantly among treatments. Hazard ratio was greatest for Entrust followed by its combination with entomopathogenic fungi, and lowest for neem oil. Antifeedant assays were also conducted to determine if these strains also exhibited antifeedant behavior in C. formicarius elegantulus and if these natural bioinsecticides enhanced antifeedant behavior when used in combination. Using a choice arena for each strain-treated chip with the control, insects were fed for 24 hours after which chips were assessed for feeding holes. There was no difference in antifeedant index between the strains at a particular concentration. However, when entomopathogenic fungi (Mp-K048 and Ma-K056) were used in combination with Entrust and neem oil, Entrust exhibited highest antifeedant index which was similar whether used alone or in combination, but significantly different from other treatments. The antifeedant index was lowest for neem oil and its combination with entomopathogenic fungi. Past findings suggest that Metarhizium strains can colonize sweetpotato and promote plant growth parameters. We performed a greenhouse experiment to evaluate if these strains could colonize the sweetpotato slips and promote plant growth. We found initial evidence for Metarhizium strain colonization. Further experiments will need to be conducted to confirm.

Date

11-15-2023

Committee Chair

Davis, Jeffrey A.

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Entomology Commons

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