Seasonal abundance of aphids (Homoptera : Aphididae) in wheat and their role as barley yellow dwarf virus vectors in the South Carolina coastal plain

Aphid (Homoptera: Aphididae) seasonal flight activity and abundance in whea t, Triticum aestivum L., and the significance of aphid species as vectors o f barley yellow dwarf virus were studied over a nine-year period in the Sou th Carolina coastal plain. Four aphid species colonized wheat in a consiste nt seasonal pattern. Greenbug, Schizaphis graminum (Rondani), and rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki),colonized seedling wheat imm ediately after crop emergence, with apterous colonies usually peaking in De cember or January and then declining for the remainder of the season. These two aphid species are unlikely to cause economic loss on wheat in South Ca rolina thus crop managers should not have to sample for tile subterranean R . rufiabdominalis colonies. Bird cherry-oat aphid, Rhopalosiphum padi (L.), was the second most abundant species and the most economically important. R hopalosiphum padi colonies usually remained below 10/row-meter until peakin g in February or March. Barley yellow dwarf incidence and M heat, yield los s were significantly correlated with R. padi peak abundance and aphid-day a ccumulation on the crop. Based on transmission assays, R. padi was primaril y responsible for vectoring the predominant virus serotype (PAV) we found i n wheat. Pest management efforts should focus on sampling for and suppressi ng this aphid species. December planting reduced aphid-day accumulation and barley yellow dwarf incidence, but delayed planting is not a practical man agement option. English grain aphid, Sitobion avenae (F.), was the last spe cies to colonize wheat each season, and the most abundant. Sitobion avenae was responsible for late-season virus transmission and caused direct yield loss by feeding on heads and flag leaves during an outbreak year.