SEASONAL ABUNDANCE OF APHID VECTORS OF POTATO-VIRUS-Y IN THE RED RIVER VALLEY OF MINNESOTA AND NORTH-DAKOTA

An epidemic of aphid-transmittttd potato virus Y (PVY) in seed potato grown in in the Red River Valley of Minnesota and North Dakota was the reason we began a study to determine which aphid species sere found i n traps placed near potato fields. Knowledge of which aphid species ar e present and which of these are known vectors of PVY is needed to dev elop management strategies that minimize virus spread. The spread of P VY to healthy indicator plants and captures of alate aphids in tile tr aps were monitored weekly for 3 vr consecutively (1992-1994) throughou t the Red River Valley. Thirty-four aphid species were identified from green and yellow tile traps in 1992, 25 in 1993, and 26 in 1994. Yell ow tile traps caught significantly more aphids overall than green tile traps and were significantly preferred by Aphis helianthi Monell, Cap tophorus elaeagni (der Guercio), and Rhopalosiphum maidis (Fitch), Int ervals of greatest aphid capture in green traps were generally between mid-July and mid-August at all sites in all 3 yr. Aphid captures at a ll sites were 3-25 times greater in 1992 and 1994 than in 1993. PT;Y i nfection of indicator plants exposed at the trapping sites also was gr eater in 1992 (25 plants) and 1993: (18 plants) than in 1993 (2 plants ). Eighty-nine percent of PVY spread to indicator plants occurred betw een 8 July and 19 August. Eight species comprised 89.9% of the aphids collected in green traps during intervals of PVY transmission to indic ator plants: Acyrihosiphon pisum (Harris), pea aphid; A. helianthi; C. elaeagni; Lipaphis erysimi (Kaltenbach), turnip aphid; R, maidis, cor n leaf aphid; R, padi (L.), bird cherry-oat aphid; Schizaphis graminum (Rondani), greenbug; and Sitobion avenae (F.), English grain aphid. S even of these species were previously known PVY vectors. We found that A. helianthi transmitted PVY with low efficiency under greenhouse con ditions. The 8 most common aphid species were associated with crops an d weeds common in the Red River Valley. Our data suggest that although the relative importance of individual PVY vectors varies from year to year and location by location, total aphid captures may be the best i ndicator of the risk of PVY spread.