SUMMARY

The occurrence of viruliferous onion thrips (Thrips tabaci) outside lisianthus greenhouses was examined from 2003 to 2005. Adults were captured using blue sticky traps placed outside the greenhouses, and virulif-erous individuals were identified using DAS-ELISA. While T. tabaci appeared from April to July, viruliferous individuals were mainly detected from the end of May to the middle of June. Leaf necrosis caused by Iris yel-low spot virus (IYSV) developed soon after the massive appearance of viruliferous T. tabaci in the field. The dis-ease appeared simultaneously in June on lisianthus plants at different growth stages. These results suggest that the infection source of IYSV is located outside the greenhouses. Surveys conducted in an onion field near the lisianthus greenhouses showed that viruliferous T. tabaci dispersed after harvesting of onions, suggesting that IYSV-infected onion plants are the inoculum sources in this area