Early-season patterns of onion thrips, Thrips tabaci (Lindeman), population densities in onion fields in New York

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a serious yield-reducing pest of onion crops worldwide.  Gaining a better understanding of early-season T. tabaci dispersal and field colonization patterns will be important for improving management of this pest.  Researchers and growers have observed, anecdotally, that T. tabaci densities are greater along field edges (i.e., an edge effect) early in the onion growing season.  To investigate this, adult T. tabaci population densities were recorded weekly in at least 46 onion fields in New York in June and early July 2011 and 2012.  Densities were recorded on plants located 10, 30, 50, 70, and 90 feet from field margins.  Results indicated that an edge effect was observed; as distance toward the center of an onion field increased, T. tabaci densities decreased significantly.  Differences in the magnitude of the edge effect were observed and influenced by adjacent habitat, however differences varied from 2011 to 2012.  Results suggest that targeting field edges for T. tabaci management may be a viable strategy early in the onion growing season, thus potentially reducing pesticide application and crop production cost.