Exchange of virus and vector populations between natural and managed habitats

Understanding the flow of vector and virus populations between managed and natural habitats is critical to managing pest and disease risk in agricultural systems. In the Palouse region of eastern Washington, field peas are grown in rotation with wheat and are attacked by the pea aphid, Acyrthosiphon pisum. While pea aphids cause little direct damage, they often serve as vectors of pea enation mosaic virus (PEMV), a crippling disease of cool-season legumes. However, the origin of the populations of PEMV and A. pisum that infest spring-planted legumes on the Palouse is currently unclear. Consequently, a survey was conducted to identify potential wild hosts of both A. pisum and PEMV during the summer of 2015. Aphid-infested legumes were identified and tested for PEMV via ELISA. A. pisum was observed on species of legume including alfalfa, birdsfoot trefoil, white clover, hairy vetch, Palouse milkvetch, sweetclover, and perennial sweatpea. Of these, only hairy vetch tested positive for PEMV. As a result, we recommend that usage of hairy vetch as a winter cover crop be carefully evaluated in areas where cool-season legumes are grown. More research is necessary, however, to determine whether the presence of hairy vetch contributes significantly to pest or disease outbreaks.