Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/17/2000
Publication Date: 4/15/2001
Citation: CHAPIN, J.W., THOMAS, J.S., GRAY, S.M., SMITH, D.M., HALBERT, S.E. SEASONAL ABUNDANCE OF APHIDS IN WHEAT AND THEIR ROLE AS BARLEY YELLOW DWARFVIRUS VECTORS IN THE SOUTH CAROLINA COASTAL PLAIN. JOURNAL OF ECONOMIC ENTOMOLOGY. 2001. Interpretive Summary: Multiple aphid species colonize winter wheat and most transmit the viruses that cause Barley Yellow Dwarf, the most economically important virus disease of cereal crops worldwide. Aphid populations, and to some extent the amount of virus disease, can be controlled by insecticide applications. To minimize the economic and environmental impact of pesticide applications, it is critical to identify the important target pest and the ideal times of treatment. This project identified the seasonal occurrence of aphid species infesting the winter wheat crop over multiple years and identified the aphids responsible for spreading BYDV into and within the crop. The study identified 4 important aphid species that infest the winter wheat crop in South Carolina each year and that are capable of transmitting the barley yellow dwarf viruses. Two aphids that infest the crop early in the growing season, and previously implicated as important virus vectors, were found not to be associated with virus disease incidence. It was recommended that insecticide treatments to control these aphids be halted. One aphid species that infests the crop during the middle of the growing season was found to be the most important aphid vector of barley yellow dwarf. One or two well-timed insecticide applications to control this one aphid can also minimize the barley yellow dwarf incidence. The treatment times coincide with midseason applications of fertilizer, which minimizes application costs. This knowledge reduces the amount of effort that growers need to expend in scouting for aphid pests and eliminates costly and ineffective insecticide applications early in the season.
Technical Abstract: Aphid seasonal flight activity and abundance in wheat, Triticum aestivum L., and the significance of aphid species as vectors of barley yellow dwarf virus (BYDV) were studied over a nine-year period in the South Carolina coastal plain. Four aphid species colonized wheat in a consistent seasonal pattern. Greenbug, Schizaphis graminum (Rondani), and rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki) colonized seedling wheat immediatel after crop emergence, with apterous colonies usually peaking in December 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 Carolina, thus crop managers should not have to sample for the subterranean R. rufiabdominalis colonies. Bird cherry-oat aphid, Rhopalosiphum padi (l.), was the second most abundant species and the most economically important. Rhopalosiphum padi colonies usually remained below 10/row-m until peaking in February or March. Barley yellow dwarf (BYD) incidence an wheat yield loss were highly correlated with R. padi peak abundance and aphid-day accumulation on the crop. Based on transmission assays, R. padi was primarily responsible for vectoring the predominant PAV serotype in wheat. Pest management efforts should focus on sampling for and suppressing this aphid species. December planting reduced aphid-day accumulation and BYD incidence, but delayed planting is not a practical management option. English grain aphid, Sitobion avenae (F.), was the last species 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.