LOCALIZATION OF TOMATO SPOTTED WILT TOSPOVIRUS IN LARVAE AND PUPAE OFTHE INSECT VECTOR THRIPS SETOSUS

Changes in the accumulation of tomato spotted wilt tospovirus (TSWV) n ucleocapsid (N) protein in Thrips setosus, an insect vector, from eclo sion to 17 days were revealed by the double-antibody sandwich-enzyme-l inked immunosorbent assay (DAS-ELISA) system with individual thrips. F irst-instar larvae were fed on TSWV-infected Datura stramonium for 2 h , and then kept on healthy Vigna susquipedaris. Individuals were subsa mpled for 17 days from first-instar larval to adult stage. The N prote in concentration increased gradually from the first- to second-instar larval stage after acquisition feeding, peaking on day 5. Viral concen tration then declined drastically from the second-instar larval to pup al stage. During the adult stage after ecdysis, persistently low N pro tein titers were demonstrated by DAS-ELISA, but adult thrips could tra nsmit the virus. N protein was localized in first- and second-instar l arvae and pupae by indirect immunofluorescence. On the second to fourt h days after acquisition, specific fluorescence signals were detected within the anterior midgut that then spread to the whole midgut during the second-instar larval stage. As time elapsed, N protein was detect ed throughout the larval midgut and possibly within the salivary gland s in pupae at 6 days after acquisition. Fluorescence signals within th e pupal midgut were observed, but were not as intense as in larvae.