REPRODUCTION AND DAMAGE BY RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) AS INFLUENCED BY FUNGAL ENDOPHYTES AND COOL-SEASON TURFGRASSES

In the Pacific Northwest of the United States, certain cool-season turfgrasses grown for seed are colonized by Russian wheat aphid, Diuraphis noxia (Mordvilko). The objectives of our study were to determine which turfgrass species are colonized and damaged by the aphid, to determine if genetic resistance occurs within genotypes of the same species, and to determine if fungal endophytes enhance aphid resistance in turfgrasses. Compared with cereal species and intermediate wheatgrass (Elytrigia intermedia (Host) Nevski subsp. intermedia), turfgrass species were not as susceptible to Russian wheat aphid. Festuca spp. were better hosts than other grass species. Perennial ryegrass (Lolium perenne L. 'Repell' and 'Regal') had resistance 6 wk after infestation. Redtop (Agrostis alba L. 'Streaker'), sheep fescue (Festuca ovina L. 'Azay'), slender creeping red fescue (F. rubra subsp. litoralis 'Logro'), and tall fescue (F. arundinacea Screb. 'Mustang,' 'Apache,' and 'Rebel') had intermediate resistance to Russian wheat aphid feeding. 'Repell' and 'Regal' were infected with a fungal endophyte, Acremonium lolii Latch, Christenson, & Samuels. 'Mustang' was infected with Acremonium coenophialum Morgan-Jones & Gams, and 'Wrangler' was infected with an unidentified species of Acremonium. Sheep fescue 'Bighorn' and strong creeping fed fescue (F. rubra L. subsp. rubra, 'Ruby') were infected with Epichloe typhina (Pers. ex Fr.) Tul. 'Repell' and 'Regal' showed the greatest resistance to aphid feeding, suggesting that plant resistance may have been enhanced by the presence of fungal endophytes. Observations suggest that Russian wheat aphid survival was better on isogenic lines of endophyte-free tall fescue and that nymphs were more sensitive to the presence of fungal endophyte than adults. Researchers in the areas of plant resistance and germplasm screening for genetic resistance to aphids must be cognizant of fungal endophyte and its effect on aphid biology.