In 2003, commercial growers in New York and Pennsylvania reported losses of up to 30% in late-planted snap bean crops with symptoms of infection by Cucumber mosaic virus (CMV). Although the ability of local populations of aphids to transmit CMV to snap beans had not been studied, it was noted that localized epidemics coincided with the migration of large populations of Aphis glycines, the soybean aphid. Potential CMV vectors were identified by weekly trapping in NY and PA snap bean fields in 2004 and 2005. Dominant species were then compared for CMV vectoring efficiency. The probability (p) of CMV transmission by single A. glycines was estimated to be 8% from multiple-vector-transfer (MVT) tests using 10 aphids per plant with acquisition by random-access on detached leaves. MVT-derived estimates of p were consistent with that obtained from single-vector-transfer (SVT) tests (mean of 9.5%) using observed timed acquisition probes. MVT testing was as reliable as SVT in estimating vector transmission efficiency. The most efficient vectors identified by MVT tests included: Aphis glycines, A. gossypii, A. pisum, and Rhopalosiphum maidis. Results support the hypothesis that epidemics of CMV in snap beans could be associated with late-summer migrations of A. glycines, as well as other species.