For a time, it was the most destructive pest in California alfalfa. It received a substantial amount of research and extension interest resulting in 9 California Agriculture articles between 1956 and 1963. These covered a wide range of topics including development of resistant varieties, identification of natural enemies and pathogens to the pest, and chemical control and application trials.
In learning to manage this pest, entomologists from University of California formed the concept of “integrated control”, the direct precursor of integrated pest management.
Through a combination of management approaches which emphasized the role of naturally occurring predators and parasites of spotted alfalfa aphid (SAA) and the use of selective insecticides, the problem was brought under control. The long term solution proved to be the incorporation of host plant resistance into regionally adapted alfalfa varieties.
SAA is still present in California and can be found at low levels almost every year. The pest is most commonly encountered in summer in the Central Valley and in the fall and winter in southern desert valleys. Monitoring and assessment procedures developed many decades ago are still relevant and should be followed. While monitoring consists of dislodging aphids from a stem and counting, adjusting your threshold based on the length of the stem sampled. http://www.ipm.ucdavis.edu/PMG/r1900611.html
SAA is one of several aphids which should be monitored closely. A collection of photos for common aphids in alfalfa can be seen on the UC IPM website.