Diurnal dispersal of onion thrips, Thrips tabaci (Lindeman), in an onion ecosystem

Many insects engage in long-distance (non-trivial) dispersal in temperate regions, particularly during crepuscular hours nearest sunset.  Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a serious yield-reducing pest of onion crops worldwide, and it is also the principal vector of Iris yellow spot virus (IYSV), a damaging pathogen of onion crops.  Thrips tabaci is known to engage in short-distance flight (trivial), but its propensity to engage in long-distance dispersal, the time during the day in which it might do so, and whether thrips engaging in long-distance flight carry IYSV are not known.  To address these questions, thrips dispersal was monitored during the onion-growing season using adhesive traps placed at five heights (canopy level to 18 ft) and monitored over 120 hours (5 sampling periods per day, for 5 days) in four onion fields.  A subset of trapped T. tabaci was tested for IYSV.  This study was conducted in June, July, and August in both 2012 and 2013.  Results from 2012 indicated that T. tabaci typically disperses in greatest numbers during the hour before sunset (46.8% of thrips dispersing over a 24 hr day), overall dispersal is greatest in August (325 times more than June; 5 times more than July), many engage in long-distance flight (24.9%), and some T. tabaci tested positive for IYSV (June = 2.3%, July = 2.2%, August = 31.9%; 22.9% overall).  These results have implications for both T. tabaci and IYSV management.