Tissue tropism related to vector competence of Frankliniella occidentalis for tomato spotted wilt tospovirus

The development of tomato spotted wilt tospovirus (TSWV) infection in the m idgut and salivary glands of transmitting and non-transmitting thrips, Fran kliniella occidentalis, was studied to elucidate tissue tropism and the vir us pathway within the body of this vector. Immunohistological techniques us ed in this study showed that the midgut, foregut and salivary glands were t he only organs in which virus accumulated. The first signals of infection, observed as randomly distributed fluorescent granular spots, were found in the epithelial cells of the midgut, mainly restricted to the anterior regio n. The virus subsequently spread to the circular and longitudinal midgut mu scle tissues, a process which occurred late in the larval stage, In the adu lt stage, the infection occurred in the visceral muscle tissues, covering t he whole midgut and foregut, and was abolished in the midgut epithelium. Th e infection of the salivary glands was first observed 72 h post-acquisition , and simultaneously in the ligaments connecting the midgut with these glan ds. The salivary glands of transmitting individuals appeared heavily or com pletely infected, while no or only a low level of infection was found in th e glands of non-transmitting individuals. Moreover, the development of an a ge-dependent midgut barrier against virus infection was observed in second instar larvae and adults. The results show that the establishment of TSWV i nfection in the various tissues and the potential of transmission seems to be regulated by different barriers and processes related to the metamorphos is of thrips.