Selection of tomato spotted wilt virus for vector specificity among thrips vectors Frankliniella occidentalis, F. fusca, and Thrips tabaci

Mechanisms and interactions underlying the specific nature of insect vector-virus interactions responsible for virus infection and transmission are poorly understood for insect-transmitted plant viruses.  This type of information would be valuable for understanding the dynamics driving the epidemiology and evolution of these viruses.  In this study, using Tomato spotted wilt virus (TSWV) and three of its primary thrips vectors, Frankliniella occidentalis, F. fusca, and Thrips tabaci, we hypothesized that the transmissibility of a TSWV isolate transmitted by all three vector species would change following repeated transmission of the isolate by a single vector species.  Four field collected TSWV isolates originally collected from tobacco were mechanically inoculated into Emilia sonchifolia plants in the laboratory.  Three lines of each isolate were then established: one that we transmitted exclusively with Frankliniella fusca, one we transmitted exclusively with Frankliniella occidentalis, and one we transmitted exclusively with Thrips tabaci. Each line was maintained through at least 5 rounds of transmission by each respective vector species, and TSWV infected plant material from each round was saved and stored at -80°C.  Each vector species was then tested for its ability to transmit 1) the initial field collected isolate, 2) the isolate from the last round of transmission in the F. fusca line, 3) the isolate from the last round of transmission in the F. occidentalis line, and 4) the isolate from the last round of transmission in the Thrips tabaci line. All three species were tested for their ability to transmit each group of 4 isolates concurrently. The results of these transmission studies and their implications for thrips transmission of tospoviruses will be discussed.