Distinct Levels of Specificity in Thrips Transmission of Tospoviruses

Various thrips species were tested for their ability to transmit different tospovirus species using a petunia leaf disk assay system. Transmission efficiencies were determined for four species of thrips and four tospovirus species : tomato spotted wilt virus (TSWV), impatiens necrotic spot virus, tomato chlorotic spot virus (TCSV), and groundnut ringspot virus (GRSV). Frankliniella occidentalis appeared to be the most efficient vector for the four tospovirus species tested. A dark form of E schultzei transmitted three (TSWV, TCSV, and GRSV) of the four tospoviruses, whereas a light form of this species transmitted TSWV and TCSV rather poorly. E intonsa, which has been documented as vector of TSWV, although transmission data were not presented, transmitted TSWV efficiently and TCSV at a very low frequency. Strikingly, only one of four populations of Thrips tabaci from different geographic regions was able to transmit one of the tospoviruses tested (TSWV) and this at a low efficiency. Enzyme-linked immunosorbent assay (ELISA) showed that virus could be readily detected in transmitting adult thrips. Viral antigen also could be detected in some individuals that did not transmit virus to petunia leaf disks, but the amount of virus detected was consistently lower than those of transmitters. Positive ELISA values were found only for thrips-tospovirus combinations in which virus transmission could occur, whereas negative ELISA scores were observed for all individuals from thrips-virus combinations in which no virus transmission took place, indicating that acquisition of the virus did not result in replication and accumulation of these viruses in thrips.