Onion thrips, Thrips tabaci Lindeman, is an important agricultural pest worldwide. T. tabaci damages crops by feeding on leaves and by transmitting plant pathogens, including Iris yellow spot virus (Bunyaviridae: Tospovirus) (IYSV). T. tabaci and IYSV are perennial problems for New York's onion industry, and research is needed to improve our understanding about T. tabaci biology, ecology and IYSV epidemiology for developing better management programs. This dissertation examines the patterns of T. tabaci dispersal and colonization of onion crops. Clear sticky card traps and trap-equipped unmanned aerial vehicles (UAVs) were used to monitor the seasonal dispersal patterns of T. tabaci and IYSV. Most T. tabaci were captured below 2 m, while an average of 4% were captured above 2 m. Viruliferous T. tabaci were captured with both card traps and UAVs, and proportions increased through the growing season each year. T. tabaci dispersal activity below 6 m was observed to effectively cease at nightfall, while highest densities were observed during the evening crepuscular period. T. tabaci dispersal activity and temperature tended to be positively correlated, while negative correlations were observed with wind speed. Commercial onion fields were sampled in three onion growing regions to identify the effect of adjacent habitat on patterns of T. tabaci colonization of onion fields. Early-season densities of adult T. tabaci were not affected by adjacent habitat in 7 of 9 cases, while edge effects were observed in 4 of 9 cases. Late-season densities were greater in onion fields adjacent to senescing onion fields, and densities in these fields were observed to decrease with increasing distance into the onion fields. These results strongly suggest that T. tabaci engage in both short- and longrange dispersal during the onion growing season, and that late-season dispersal likely contributes to the spread of IYSV. Abiotic factors such as daylight, diel cycle, temperature, wind speed and atmospheric pressure determine when T. tabaci flight is likely to occur. Early-season colonization of onion fields occurs relatively uniformly in onion crops, while senescing crops are likely the source of adult T. tabaci colonizing adjacent, non-senescing fields late in the season, prior to harvest.