A CLONE OF THE RUSSIAN WHEAT APHID (DIURAPHIS-NOXIA) AS A VECTOR OF THE BARLEY YELLOW DWARF, BARLEY STRIPE MOSAIC, AND BROME MOSAIC-VIRUSES

When Diuraphis noxia were given acquisition access feedings on plants infected with single isolates of the five strains of barley yellow dwarf virus (BYDV) and then confined on oats or barley test plants for inoculation, none of 643 plants became infected. When D. noxia were placed on barley stripe mosaic virus (BSMV)-infected plants and subsequently confined on barley test seedlings, none of 165 plants became infected. Only three of 302 barley seedlings developed symptoms typical of brome mosaic virus (BMV) infection following inoculation access feedings by aphids previously fed on BMV-infected sources. However, enzyme-linked immunosorbent assay showed 19 of these plants were positive for BMV, suggesting symptomless infections. When D. noxia were fed on barley doubly infected with BSMV and BMV, little difference in transmission efficiency was observed. No transmission of BSMV occurred, and only one of 88 plants became infected with BMV. When aphids were given acquisition access feedings on barley doubly infected with the PAV isolate of BYDV and BMV, three of 301 test plants became infected with PAV and one with BMV. When D. noxia were exposed to the Rhopalosiphum padi virus (RhPV) while feeding on plants infected with BYDV-PAV and BMV, 19 of 229 test plants became infected with PAV. Ultrastructural studies indicated that D. noxia exposed to RhPV by feeding on virus-contaminated plants or on virus-sucrose solutions through membranes acquired the virus and developed typical cytopathological symptoms. When all transmissions from all experiments were combined, D. noxia at densities of up to 50 aphids per plant transmitted BMV to 2.5% and BYDV-PAV to 2.8% of all plants infested with RhPV.