Thrips tabaci (Thysanoptera: Thripidae) transmission studies of Iris yellow spot virus (IYSV) using onion seedlings

Iris yellow spot virus (IYSV) (family Bunyaviridae; genus Tospovirus) causes serious losses to bulb and seed onions in USA. The onion thrips, Thrips tabaci (Lindeman) is the only confirmed vector of IYSV. However, there is no information available on protocols for conducting routine transmission assays. Through this study we intend to establish one such protocol and optimize parameters like the host plant stage for inoculation, density of thrips for inoculation, and inoculation access period. We conducted IYSV -transmission using a simple test tube assay. Three leaf stage onion seedlings (CV Pegasus) were placed in 20×150 cm glass test tubes covered with a copper mesh (178 microns) and sealed with parafilm. Varying numbers (1, 4, 8, and12) of nymphs/adult thrips that developed on IYSV-infected onion plants were introduced into the seedling tubes for different inoculation access periods (15 min, 30 min, 1h, 6 h, 24 h, and 120 h). Seedlings with adult thrips from healthy onion plants served as negative controls. The assay set up was left undisturbed in a growth chamber at 25oC and 12 hour day length until further testing. Infection status of the seedlings was tested using double antibody enzyme linked immunosorbent assay (DAS ELISA) two weeks post inoculation. Results revealed that IYSV transmission increased with increase in thrips density. Transmission efficiency also increased with prolonged inoculation access periods than shorter inoculation access periods. The transmission efficiency ranged from 31-94%. , This optimized protocol has yielded consistent results and can be adopted easily for routine transmission assays.