Summary auto-generated
This study investigated how tomato spotted wilt tospovirus (TSWV) establishes infection in different tissues of the thrips vector Frankliniella occidentalis and how this relates to transmission competence. Using immunohistological techniques, researchers tracked virus infection from acquisition through larval development to adulthood. The virus first appeared in midgut epithelial cells of the anterior region, then spread to surrounding muscle tissues. In adults, the midgut epithelium cleared the infection, but muscle tissues remained infected. Virus reached the salivary glands 72 hours post-acquisition, and heavily infected salivary glands correlated with successful transmission. The study identified age-dependent barriers that prevented virus establishment when acquired by adults or second instar larvae, explaining why only early-stage larvae can acquire and transmit TSWV. The findings demonstrate that vector competence depends on multiple tissue-specific barriers and developmental processes related to thrips metamorphosis.
Key findings
- TSWV infection begins in anterior midgut epithelial cells and progressively spreads to muscle tissues; infection is cleared from epithelium during adult development but persists in muscles
- Heavy infection of salivary glands correlates with transmission capacity, while limited or absent salivary gland infection marks non-transmitting individuals despite midgut infection
- Age-dependent barriers prevent virus acquisition by adult thrips, with only early first-instar larvae capable of acquiring replicating virus infections
- The midgut infection barrier in adults represents a key factor limiting vector competence, preventing virus establishment when ingested by mature thrips
- Multiple developmental barriers operating at different tissues and life stages regulate TSWV establishment and transmission potential in F. occidentalis
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Abstract
The development of tomato spotted wilt tospovirus (TSWV) infection in the midgut and salivary glands of transmitting and non-transmitting thrips, Frankliniella occidentalis, was studied to elucidate tissue tropism and the virus pathway within the body of this vector. Immunohistological techniques used in this study showed that the midgut, foregut and salivary glands were the 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 region. The virus subsequently spread to the circular and longitudinal midgut muscle tissues, a process which occurred late in the larval stage. In the adult stage, the infection occurred in the visceral muscle tissues, covering the whole midgut and foregut, and was abolished in the midgut epithelium. The infection of the salivary glands was first observed 72 h post-acquisition, and simultaneously in the ligaments connecting the midgut with these glands. The salivary glands of transmitting individuals appeared heavily or completely infected, while no or only a low level of infection was found in the glands of non-transmitting individuals. Moreover, the development of an age-dependent midgut barrier against virus infection was observed in second instar larvae and adults. The results show that the establishment of TSWV infection in the various tissues and the potential of transmission seems to be regulated by different barriers and processes related to the metamorphosis of thrips.