The transmission of tomato spotted wilt tospovirus (TSWV) by Thrips tabaci collected from leek was studied using the petunia local-lesion leaf-disc assay. After an acquisition-access period of 72 h given to newborn larvae up to 8 h old, the efficiency of transmission by adults was determined in three inoculation-access periods of 48 h. This efficiency varied for six T. tabaci populations from 0.7 to 11.6␒n experiments using the Greek TSWV isolate GR-04. Males were more efficient transmitters than females (19 out of 176 versus five out of 494). Frankliniella occidentalis transmitted the same virus with a higher efficiency (34.8Ž The transmission rate differed also among TSWV isolates, as shown in tests with four T. tabaci using two isolates. The virus was more efficiently acquired from infected leaf material of Datura stramonium than from that of Emilia sonchifolia. Plants of the latter species were more susceptible than Nicotiana tabacum in thrips transmission tests.