Are late season, non-systemic infections of tomato fruit by tomato spotted wilt virus due to fruit or flower feeding by western flower thrips (Frankliniella occidentalis)?

Tomato spotted wilt virus (TSWV) is transmitted by at least 8 species of thrips (Family Thripidae) in a persistent, propagative manner to over 1000 plant species, including tomato (Solanum lycopersicum) and several other important crops. Early season transmission of TSWV to young tomato plants leads to severe infections that result in the production of few if any marketable fruit. In response, breeders have developed resistant varieties but resistance-breaking (RB) isolates of the virus occur worldwide. A common problem encountered in TSWV-resistant tomato varieties is the development of non-systemic, late season infections that are limited to the fruit. It is not known why these infections occur and if RB isolates are responsible. We tested the hypothesis that both RB and non-RB isolates can be transmitted by western flower thrips (Frankliniella occidentalis) to individual fruit of TSWV-resistant and TSWV-susceptible tomato lines through direct feeding on either the flower blossoms or developing fruit. We also investigated whether the virus can be spread from fruit to fruit leading to within field spread of TSWV.