EVALUATING INTERACTIONS BETWEEN ONION THRIPS AND ASSOCIATED PLANT PATHOGENS AND METHODS TO IMPROVE MANAGEMENT IN ONION

The success of integrated pest management (IPM) programs relies on pest biology and ecology, and the tactics to manage damage caused by those pests. In onion production, onion thrips (Thrips tabaci) and their associated plant pathogens are primary constraints to crop production. The objectives of this work were to 1) evaluate IPM tactics to reduce damage caused by onion thrips and associated plant pathogens, 2) further characterize the relationship between onion thrips and iris yellow spot virus (IYSV), and 3) determine the success of extension programming to increase grower adoption of insecticide resistance management and IPM tactics for onion thrips. In chapters 1 and 2, a combination of different IPM tactics (host plant resistance, fertility regimes, and insecticide programs) was evaluated to reduce onion thrips densities and severity of associated plant diseases, namely IYS disease and bacterial bulb rot. In these trials, fertility regime did not consistently affect onion thrips densities, IYS disease, or bacterial bulb rot. Insecticide use consistently reduced onion thrips densities, IYSV disease, but not the incidence of bacterial bulb rot. Additionally, a thrips resistant cultivar (‘Avalon’) experienced lower thrips densities and IYS disease severity but suffered from greater levels of bacterial rot. In chapter 3, there is discussion about the potential role that different habitats within the onion production system may have as a source for IYSV inoculum (viruliferous onion thrips). In these trials, transplanted onion fields accounted for 49-51% of the total estimated numbers of viruliferous thrips, which may generate inoculum for late-season outbreaks of IYSV. In chapter 4, I describe a laboratory study that evaluated the effect of IYSV infection on the reproduction and mortality of adult onion thrips. Reproduction did not differ between groups, but viruliferous adults lived 1-6 days longer than non-viruliferous adults. Lastly, in chapter 5, the effectiveness of an extension-based program was investigated to increase grower adoption of IPM tactics for onion thrips. The program was successful, and growers increased use of insecticide class rotation by 31% and use of the action threshold by 44%. These studies improved our understanding about the biology and ecology of onion thrips and IYSV and described methods that will improve onion thrips management in onion