Document Type

Master's Research

Degree Name

Master of Science

Department

Biology

Advisor(s)

Punya B. Nachappa

Date of Award

12-2015

Abstract

Soybean vein necrosis virus (SVNV) is a new viral disease infecting soybean crops in the United States. Since its discovery in 2008, it has since spread to infect many states in the US and has also been detected in Ontario, Canada. SVNV has been identified as being a new virus in the genus Tospovirus, which are typically transmitted or vectored by thrips. Thrips species make up a large proportion of arthropods found in soybean fields, sometimes accounting for up to half of the arthropods collected. So far, only soybean thrips have been confirmed to transmit SVNV. However, eight other species of thrips are found in soybean fields, including eastern flower thrips and tobacco thrips. The goal of my thesis project is to improve our understanding of the plant pathogen, SVNV, and the thrips vectors of SVNV. There were two main objectives of the project.

The first objective was to determine SVNV incidence and seasonal patterns of thrips abundance in soybean fields, and to determine the effects of weather on these two factors. SVNV was quite widespread during the 2013 and 2014 growing seasons in Indiana. Virus incidence as well as thrips abundance showed seasonal patterns, with SVNV symptoms being detected in August, coinciding with the highest incidence of thrips. Weather parameters, such as degree day and rainfall index varied in their ability to predict the abundance of different species in the field. Cumulative degree day was the most useful parameter in predicting soybean, eastern flower, and tobacco thrips abundance using short term weather data. However, the rainfall index became more important in determining thrips abundance over the long term for soybean thrips.

The second objective was to determine the life history traits of infected and uninfected soybean thrips as well as the life history traits of different species of thrips on soybean. Total fecundity was the only life history trait studied that showed a significant difference between SVNV-infected and –uninfected soybean thrips. However, this is the first report that shows that SVNV infection has a direct negative impact on soybean thrips vectors. Soybean thrips also showed the highest fecundity on soybean out of the three species studied. Outcomes of this study will increase the known information and understanding of population dynamics of SVNV and thrips vectors in the field, as well as the life history traits of known and potential vectors of SVNV, all of which will be beneficial in implementing management strategies to control the spread of SVNV.

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