Semester of Graduation

Summer 2023

Degree

Master of Science (MS)

Department

Entomology

Document Type

Thesis

Abstract

Sweetpotato, Ipomoea batatas (L.) Lam, is the number one vegetable crop in Louisiana, producing 21,178 kg/ha in the year 2021. The sweetpotato weevil, Cylas formicarius elegantulus (Summers), is an economically important pest of sweetpotato. C. formicarius elegantulus females lay eggs into feeding holes on the storage root surface. Larvae then hatch and tunnel through the sweetpotato flesh where they complete their development. This cryptic-natured brentid can cause up to 100% yield loss when left unmanaged. The Louisiana Department of Agriculture and Forestry mandates protocols to limit C. formicarius elegantulus spread (e.g., clean seed, pheromone trapping, and quarantines); however, scheduled chemical application is the primary control method. Our research looked to incorporate biological control and host-plant resistance in C. formicarius elegantulus management. Commercially available entomopathogenic fungi, Beauveria bassiana (BoteGHA ES) and Metarhizium anisophliae (MetMaster) were tested against bifenthrin (Brigade 2EC) on different sweetpotato varieties in the laboratory, greenhouse, and field. Brigade 2EC consistently caused the highest mortality and exhibited the longest residual activity. MetMaster provided no control at any levels, but BoteGHA ES caused up to 83% mortality in laboratory and greenhouse assays. BoteGHA degradation in the field is thought to be the result of abiotic environmental factors like UV or rainfall. There were no differences in product efficacy across varieties. To examine the behavioral preferences for each variety, we determined that females preferred to oviposit eggs on sweetpotato storage roots with periderm intact versus removed across multiple assays. Gravid C. formicarius elegantulus females preferred to oviposit on the resistant variety Murasaki compared to all others tested yet oviposition on this variety resulted in the lowest adult emergence. This suggests that there are induced or constitutive factor(s) that inhibit insect development in Murasaki. Additionally, differences in adult emergence from storage roots collected from different field sites confirm plant resistance is phenotypically plastic across multiple growing environments. Future research to elucidate mechanisms underlying the current results will aid grower decision-making, identification of resistance mechanisms, and product development to withstand field level degradation.

Date

7-8-2023

Committee Chair

Davis, Jeffrey A.

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