Identification of Dictyothrips betae as the vector of Polygonum ring spot virus

Dictyothrips betae (Thysanoptera: Thripidae) is the predominant thrips species on Polygonum convolvulus and Polygonum dumetorum plants infected with a recently described tospovirus species, Polygonum ring spot virus (PolRSV). Laboratory transmission experiments (leaf disk assays) with adults collected directly in the field demonstrated the competence of this thrips to transmit PolRSV, although only at a rate of 4%. However, this increased to 16% using newly emerged larvae fed on infected leaves. Frankliniella occidentalis and Thrips tabaci failed to transmit PolRSV in leaf disk assays. Reverse transcription-polymerase chain reaction (RT-PCR) with specific primers for the N protein and Western blot analysis of adult thrips to detect the N protein confirmed the presence of the virus in D. betae individuals after feeding for at least 5 days on healthy plants. For molecular identification purposes partial sequences of mitochondrial cytochrome c oxidase subunit I (COI), nuclear 28S ribosomal DNA and the elongation factor-1 alpha (EF-1 alpha) from D. betae were cloned. COI sequence was also used for deriving a phylogenetic tree, including D. betae. The results confirmed a relationship between this species and tospovirus-transmitting insects of the genus Thrips.