Resistance in Alfalfa to a Red Form of the Pea Aphid (Homoptera: Aphididae)

A red form of Acyrthosiphon pisum , (Harris) was collected from alfalfa at two locations in Maryland in 1979 to 1981. Twenty-two alfalfa lines or cultivars were evaluated for resistance to this form in laboratory tests for screening seedlings. Of the 19 lines or cultivars tested that have been classified as resistant to the green form of the pea aphid, only the lines BAA-15 and PA-1 and the cultivar ‘CUF-101’ exhibited high resistance to the red form. ‘Cascade,’ WL 219, WL 311, and WL 313 showed low resistance levels. Resistant segregates occurred in most of the entries tested, indicating that selection for germplasm improvement is possible.