Onion thrips (OT), Thrips tabaci Lindeman are an economic pest of Allium crops around the world. In Ontario, Canada, the 2001 farm-value of onions approached $21 M. Recent OT-control problems have stimulated research to improve OT-management programs for Ontario onion growers. Better understanding of OT field-biology is therefore required.
Several monitoring techniques were utilized to study OT field-activity in 2001 and 2002. White sticky traps, separated by 10 m, were placed in a straight line from the field-edge into the middle of two onion fields. Due to difficulty distinguishing species on the sticky traps, a yellow (2001) or white (2002) water pan trap was also installed at each site. In 2002 a single, automated, diurnal trapping system was installed to monitor OT-activity over 24 hour periods. Diurnal activity data will be correlated with wind direction and speed, temperature and relative humidity. In 2002 only, white sticky pole traps determined spatial movement of OT above the plant canopy.
Our data from 2001 revealed that OT-populations began to increase in mid-July. OT first appeared on traps closest to the field-edge. Populations peaked at both sites mid-August and were significantly higher at Site 1 than Site 2. Numbers exceeded 900 OT/trap at Site 1 and reached approximately 500 OT/trap at Site 2. Data from the 2002 field season will be reported.
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