Date of Award

January 2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Ian Kaplan

Committee Member 1

Joseph M Anderson

Committee Member 2

Christian H Krupke

Committee Member 3

Jeffrey D Holland

Abstract

My dissertation explores the ecology of aphid-vectored viruses in Midwestern cucurbits; in particular, it focuses on identifying source populations of vectors and virus reservoirs within fields and interactions of vector aphids with land cover surrounding and within fields. Initially, I identified the most commonly occurring viruses and aphid species associated with virus infections in pumpkin fields located across Indiana. This was done by assaying cucurbit leaf tissue with multiplex-rt-PCR targeting all four aphid-vectored, nonpersistent viruses found in cucurbits (papaya ringspot virus type-W, watermelon mosaic virus type-2, zucchini yellow mosaic virus, cucumber mosaic virus) and concurrently monitoring aphid species alightment in fields throughout Indiana. Watermelon mosaic virus (WMV) was the most common infection, detected in all but one field across both years. Papaya ringspot virus (PRSV) was also detected in many fields, but not zucchini mosaic virus or cucumber mosaic virus. Therioaphis trifolii and Aphis craccivora were positively associated with PRSV, and Aphis nerii with WMV. Rhopalosiphum padi was negatively associated with WMV. No relationship between total aphid or noncolonizing species counts was found with virus infection, and an increase in total colonizing species (Aphis gossypii) trapped in fields predicted a decrease in PRSV infection. Negative relationships between aphid species alightment and virus infection in fields could result from a virus-induced reduction in pumpkin plant quality, thereby reducing abundance of a colonizing species within the field. Other virus-mediated effects in pumpkins could reduce aphid attraction to pumpkin fields as well, such as modification of the olfactory stimuli detectable by airborne aphids. I also inventoried weed species within fields and assayed samples for virus content, to investigate weed cover contributions to vector behavior or as host to virus or vector. Using land cover data from the National Land Cover Database, relationships among virus, aphids

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