Cucumber mosaic virus (CMV) is a major component of the virus complex that has become more pronounced in snap bean in the midwestern and northeastern United States since 2001. Multiple-vector-transfer tests were done to estimate the CMV transmission efficiencies (p) of the main aphid species identified in commercial snap bean fields in New York and Pennsylvania. The four most efficient vectors (p > 0.05) were Aphis gossypii, A. glycines, Acyrthosiphon pisum, and Therioaphis trifolii, which were all significant species in the migratory aphid populations in snap bean. Moderately efficient vectors (0.01 < p < 0.04) were A. spiraecola, A. craccivora, Macrosiphum euphorbiae, and Rhopalosiphum maidis. Poor vectors (p < 0.01) included A. fabae, Nearctaphis bakeri, and Myzus persicae. Only one species, Sitobion avenae, failed to transmit CMV in replicated tests. Estimates of p were consistent between different clones of the same aphid species and among three different field isolates of CMV tested. Single-vector-transfer test results for a subset of the species supported those obtained via the multiple-vector-transfer approach. Our results are consistent with the notion that A. glycines is a major vector of recent CMV epidemics in snap bean, but that species is only one of several that are involved.

Cucumber mosaic virus (CMV) has become a major limiting factor in snap bean production in the Great Lakes region of North America, and epidemics have occurred more frequently since the soybean aphid, Aphis glycines Matsumura, was introduced. Major aphid vectors of CMV epidemics were identified by statistically relating their temporal dispersal trends to the incidence of CMV. Alates were monitored weekly using water pan traps in 74 snap bean fields in New York and Pennsylvania from 2002 to 2006. Plants were tested for CMV by ELISA one time during late bloom in 2002 and 2003 and weekly over the season from 2004 to 2006. Principal vectors of CMV included Acyrthosiphon pisum (Harris), A. glycines, Aphis gossypii Glover, and Therioaphis trifolii (Monell). Among these, A. glycines and T. trifolii were likely responsible for severe CMV epidemics because they were among the most abundant species captured, they efficiently transmit CMV, and their dispersal activity was positively correlated with periods when CMV incidence was highest. Moreover, because high numbers of A. glycines and T. trifolii disperse during July and August, snap bean fields planted beyond late June are at risk for infection during early vegetative stages and are subsequently more at risk for yield loss. In contrast, plantings up to late June are less likely to become infected during early developmental stages and should escape yield loss because major vectors are dispersing infrequently. CMV-resistant or tolerant snap bean varieties should be planted after late June to reduce the risk of yield loss.