What role do alate soybean aphids (Aphis glycines) play in the spread of Soybean mosaic virus?

Soybean mosaic virus (SMV) is an aphid-vectored virus of soybean that can reduce yield by 8 to 35%. Before Aphis glycines, several species of non-colonizing aphids were considered responsible for the transmission of SMV to soybean in North America. Aphis glycines is a competent vector of SMV that forms large colonies on soybeans and migrates across large regions of the Midwest. These factors may increase the likelihood of SMV transmission within North America. To test the hypothesis that A. glycines is an important vector of SMV, we compared data sets of alate A. glycines data to the prevalence of SMV in Iowa. Data were collected during June, July, August, and September for the 2005, 2006, and 2007 field seasons. The occurrence of alate A. glycines was measured in four suction traps stationed in northwest, northeast, central and south-central Iowa. The prevalence of SMV was estimated in 9 fields (per county) and the presence or absence of SMV in each of the 99 counties of Iowa was estimated. A ratio of infected counties was determined for the nine county areas around each of the four suction traps. Ratios were used to determine if a relationship exists between alate A. glycines and SMV prevalence. We determined that during years of increased alate A. glycines populations there was a strong relationship between the alate populations and an increased SMV prevalence (R² = 81.78%). Years with lower alate A. glycines populations had lower SMV prevalence. Therefore, A. glycines is an important vector of SMV.