Screening for resistance and yield losses caused by onion thrips (Thrips tabaci Lindeman) and Iris yellow spot virus on onions

Onions, Allium cepa L., are an important crop in New York state and onion thrips (OT), Thrips tabaci Lindeman, are a devastating onion pest. OT alone can cause substantial yield losses but can be even more problematic when it occurs with Iris yellow spot virus (IYSV) transmitted by OT. IYSV was confirmed in the summer of 2006 in New York state. Since OT are difficult to control with conventional insecticides and the importance of onion production in New York, field studies on onion resistance to OT and/or to IYSV were performed in the summer of 2007 in Potter, NY. In the first experiment, 22 onion varieties were screened for resistance to OT and/or IYSV. The number of thrips larvae was counted weekly and visual leaf damage ratings were made. In another experiment, the impact of OT/IYSV interaction on plant growth was studied. There were two treatments, protected with an insecticide and the other not protected. Eight varieties showed the lowest leaf damage compared to susceptible varieties. Five of these varieties may possess antibiosis and/or antixenosis because of the lower number of thrips found on them. The other three varieties had higher number of thrips indicating possible tolerance. There was a significant reduction in plant height and weight in the varieties. Since the populations of OT in 2007 were not as high as in previous years and the incidence of IYSV was only 10%, these experiments are being repeated in Potter, NY and in Elba, NY with 47 onion varieties.