Analysis of Tomato spotted wilt virus (TSWV) transmission by Thrips setosus
Tsuda S
National Agricultural Research Center, Tsukuba, Ibaraki 305-8666, Japan.
Correspondence: shinyat@affrc.go.jp
Tospoviruses are currently known to be transmitted by at least ten species of thrips. Frankliniella occidentalis (Pergande), the western flower thrips, having a broad host range is the most common tospovirus vector insect. As documented for F. occidentalis, when Thrips setosus (Moulton), the light-brown soybean thrips, which is an endemic species in Japan, acquires Tomato spotted wilt virus as a first instar larvae, the virus enters the midgut epithelial cells, replicates, and moves to salivary glands during pupation, then the emerged adult is able to transmit the virus. The previous cellular investigations carried out only in F. occidentalis if acquisition access feeding (AAF) was first given as an adult suggested that infectivity was prevented because TSWV was unable to enter the midgut of adult thrips. In adult T. setosus given an AAF as an adult, however, the virus was found to enter and replicate in the midgut, but not in the salivary glands meaning that could not transmit the virus. Electron microscopic observations of adult T. setosus showed that no infection occurred in cells beyond the midgut epithelia, suggesting that the virus infection is limited in the epithelial cells. In contrast, when larval T. setosus was first given an AAF, the virus was found to the midgut and the visceral muscle tissue lining the midgut as that of larval F. occidentalis infected. Our findings suggest that the barrier to infectivity in adults T. setosus differs from that shown for adults F. occidentalis.
