Tomato spotted wilt virus (TSWV) in Greece: its incidence following the expansion of Frankliniella occidentalis, and characterisation of isolates collected from various hosts

Leaf samples were collected from plants with tospovirus‐like symptoms from various hosts in different regions of Greece where Thrips tabaci, Frankliniella occidentalis or both vectors occur. The viruses infecting these plants were identified with polyclonal antibodies raised against the N proteins of Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV) by ELISA. All samples tested positive for TSWV, but not for INSV. ELISA of thirty three isolates, using monoclonal antibodies against the N protein of TSWV, revealed the existence of five epitopes on the N protein. RT‐PCR tests on a few randomly‐selected isolates, using a pair of universal primers, a pair of primers specific for the L gene and a pair of primers specific for the N gene, as well as sequence analysis of a part of the S gene of one isolate, confirmed the authenticity of the virus isolated as TSWV. Host range studies showed differences in susceptibility, especially among species belonging to the Leguminosae and Cucurbitaceae. The species Beloporone guttata and Coleus sp. are reported for the first time as hosts of the virus, whereas Solanum melongena, Celosia cristata, Dianthus chinensis, Stephanotis floribunda and Catharanthus roseus were identified as new hosts of TSWV in Greece.     

Impatiens necrotic spot virus infection and feeding behavior of nematode-parasitized western flower thrips

The effects of parasitism by the nematode Thripinema nicklewoodi Siddiqi (Tylenchida: Allantonematidae) on tospovirus infection and feeding behavior of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) were studied in the laboratory. In an initial experiment, nematode parasitism reduced the numbers of adult thrips that were positive to Impatiens necrotic spot virus (INSV) by enzyme-linked immunosorbent assay (ELISA) compared to controls. Three hypotheses on possible mechanisms causing this reduction were tested. H₁: nematodes have a tendency to penetrate healthy thrips rather than INSV-infected thrips; H₂: parasitized first instar thrips are less able to acquire virus during feeding; or H₃: INSV replication is suppressed in parasitized thrips. H₁ and H₂ were proven false as we found no difference in nematode attack rate between healthy thrips and thrips that have taken up INSV and no difference in virus uptake or feeding activity between parasitized and non-parasitized larval thrips. H₃ was not supported by data from our tests (P=0.07) but remains the explanation most worthy of future investigation. Interestingly, INSV transmission was not affected by nematode parasitism even though it reduced feeding activity of adult female thrips by 81% on leaves, 38% on pollen, and 22% on honey. However, despite lowered total feeding, probing by parasitized thrips (in honey) was not reduced, and this may explain why lowered feeding did not result in lowered virus transmission.