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 in traps placed near potato fields. Knowledge of which aphid species are present and which of these are known vectors of PVY is needed to develop management strategies that minimize virus spread. The spread of PVY to healthy indicator plants and captures of alate aphids in the traps were monitored weekly for 3 vr consecutively (1992-1994) throughout 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. Yellow tile traps caught significantly more aphids overall than green tile traps and were significantly preferred by Aphis helianthi Monell, Captophorus elaeagni (der Guercio), and Rhopalosiphum maidis (Fitch), Intervals 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 all sites were 3-25 times greater in 1992 and 1994 than in 1993. PT;Y infection of indicator plants exposed at the trapping sites also was greater in 1992 (25 plants) and 1993: (18 plants) than in 1993 (2 plants). Eighty-nine percent of PVY spread to indicator plants occurred between 8 July and 19 August. Eight species comprised 89.9% of the aphids collected in green traps during intervals of PVY transmission to indicator plants: Acyrihosiphon pisum (Harris), pea aphid; A. helianthi; C. elaeagni; Lipaphis erysimi (Kaltenbach), turnip aphid; R, maidis, corn leaf aphid; R, padi (L.), bird cherry-oat aphid; Schizaphis graminum (Rondani), greenbug; and Sitobion avenae (F.), English grain aphid. Seven of these species were previously known PVY vectors. We found that A. helianthi transmitted PVY with low efficiency under greenhouse conditions. The 8 most common aphid species were associated with crops and 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 indicator of the risk of PVY spread.