Dissertations, Theses, and Capstone Projects

Date of Degree

9-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Mitchell Baker

Committee Members

Andrei Alyokhin

Jose Anadon

Amy Berkov

David Lahti

Subject Categories

Entomology | Evolution | Other Ecology and Evolutionary Biology

Keywords

spinosad, resistance, Colorado potato beetle, resistance costs, dominance

Abstract

Colorado potato beetles (Leptinotarsa decemlineata) are a major pest of cultivated potato plants worldwide. They are well-known for their ability to rapidly evolve resistance to all major classes of pesticides. Defoliation of potato plants by L. decemlineata can reduce potato yields by a considerable margin. The damage done by resistant beetles is steep and much research is focused on developing new chemical controls, especially those derived from naturally occurring compounds. Spinosad is a relatively new natural product insecticide, introduced approximately a decade ago, suitable for use in organic farming. Potato beetles on Long Island, NY developed very strong resistance to spinosad earlier in this decade. In order to assess the level of resistance and to what degree it has reverted towards susceptibility in the past half decade, A survey of spinosad resistance in L. decemlineata was conducted on Long Island. Strong resistance is tied to overuse of spinosad on several fields. Resistance has partially reverted since beetle control using spinosad failed and its use was discontinued. This finding implies that there may be evolutionary trade-offs associated with spinosad resistance. A set of traits were examined to attempt to determine if those potential trade-offs were related to reproductive fitness. There was a negative relationship between resistance level and egg development time, providing evidence for pleiotropic effects of resistance. Evidence was also found against pleiotropy from fitness indices that showed no relationship between resistance and general reproductive fitness. Dominance of resistance is an important factor in determining pest control strategies. So to clarify the level of dominance of spinosad resistance in separate populations, we investigated colonies of L. decemlineata in Michigan, Maine, and Long Island. There was considerable variation in dominance between each site in 2010 but none of the sites were significantly different from additive resistance. In 2012, resistance on Long Island was significantly different from additive but not significantly different from fully recessive. This finding could indicate the spread of resistance alleles from the most resistant fields across the eastern part of the Island. Widespread, recessive resistance to spinosad in L. decemlineata on Long Island is theoretically easier to manage as long as resistance is costly to the beetles.

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