Date of Award

Fall 12-23-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Entomology

Advisor

Andrei Alyokhin

Second Committee Member

Angela Mech

Third Committee Member

Philip Fanning

Abstract

The Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) is one of the most destructive pests of the cultivated potato, Solanum tuberosum. Colorado potato beetles have been devastating potato crops for the past 150 years and have expanded their range during that time, becoming a globally distributed agricultural pest. Potato beetles are well-suited to agricultural environments and have evolved some degree of resistance to virtually all chemical insecticides. As such, the development of novel control methods to both control potato beetle populations and manage the evolution of insecticide resistance are in constant demand

The knockdown of gene functioning through ribonucleic acid interference (RNAi) has been demonstrated in Colorado potato beetles, suggesting the use of this technology as a means of beetle management. A novel double-stranded RNA (dsRNA) based insecticide (ledprona) has been developed for the control of Colorado potato beetle populations. The lethal and consumptive effects of ledprona have been tested in variable dose laboratory bioassays, followed by field studies. Exposure to ledprona resulted in both increased beetle mortality and decreased foliage consumption in all four instars and adult beetles. Effects decreased from earlier to later life stages. No ovicidal activity was detected. Onset of mortality was slower compared to the existing chemical insecticides.

Exposure to sublethal concentrations of ledprona on fourth instar potato beetles resulted in a lowered amount of successful pupation. Sublethal exposure of adults significantly reduced their mobility and propensity to walk after seven days and significantly decreased beetle fertility. Regarding reproduction, sublethal exposure has a stronger effect on females that was more pronounced when exposed before reaching sexual maturity. Additionally, exposure to a low concentration of dsRNA-GFP had significant, negative effects on reproduction.

Geographically distinct potato beetle populations are known to vary in their response to insecticides, including experimental compounds based on RNAi. We tested mortality and foliage consumption of beetles from different US populations treated with ledprona. We also tested the same parameters in the beetles from the same population but treated with ledprona diluted in water obtained from different populations in the US. There was slight but significant variation in the consumptive and lethal effects of ledprona among geographically distinct populations. Potato beetles collected from upstate New York exhibited significantly higher tolerance to ledprona than beetles from the other tested populations. The lethal effects of ledprona slightly varied when diluted in different water samples but there was little evidence that water chemistry affected foliage consumption.

Overall, the results of this body of work demonstrated that while ledprona’s efficacy is influenced by geographical variation, it has the ability to become a useful tool in controlling Colorado potato beetle populations and is likely to be a good fit in integrated pest management protocols because of its lethal and sublethal effects.

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