"Onion thrips (Thrips tabaci), a cosmopolitan pest of onion, are known vectors of Pantoea agglomerans, causal agent of bacterial leaf blight, and P. ananatis, causal agent of bacterial center rot. The objectives of this thesis were to determine the relationship between onion thrips and P. agglomerans under field conditions, investigate the effectiveness of combining insecticides and bactericides for managing both onion thrips and bacterial leaf blight and determine the role of feeding injury by onion thrips in influencing the pathogenicity of P. ananatis. In the first study, positive correlations between thrips population density, proportion of thrips positive for P. agglomerans and bacterial leaf blight incidence in onion fields were determined. In the pesticide trial conducted in 2015 and 2016, insecticides reduced both onion thrips abundance and bacterial leaf blight incidence, while bactericides showed no effect on reducing bacterial leaf blight symptoms. In the laboratory study significant positive correlations were determined between the number of thrips per plant and the severity of leaf blight symptoms as well as the percentage of feeding damage and the severity of leaf blight symptoms. Lastly, by utilizing a GFP-tagged strain of P. ananatis, the colonization of onion thrips feeding injury by P. ananatis was observed using fluorescence microscopy. These studies suggests that onion thrips play a significant role in the development of bacterial leaf blight and center rot in onions. Results from the pesticide trial indicate that thrips feeding damage is positively correlated with bacterial leaf blight incidence. Therefore, in order to improve bacterial disease suppression in onions, management efforts should focus on reducing onion thrips populations."--Page ii.
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