Ten alfalfa clones, Medicago sativa L., were tested at 60°, 70° and 80° F. in Kansas and Quebec for resistance to pea aphid biotypes, Acyrthosiphon pisum (Harris), originating in the respective areas.
The resistance of the clones at the three temperatures varied differentially at the two locations. One clone was resistant at all temperatures to aphids of both locations. Results indicated that biotype C61-86 of the pea aphid at St. Jean, Quebec, is biologically different from the population of the same species in Kansas. Results also suggest the possibility of finding or combining clones so that varieties of alfalfa resistant to pea aphids over broad geographic areas and environmental conditions can be secured.