A Biotype of the Spotted Alfalfa Aphid on Alfalfa

Abstract

In February 1958, near El Centro, California, symptoms of susceptibility to the spotted alfalfa aphid (Therioaphis maculate (Buckton)) were observed in the previously resistant alfalfa clone N(evada)-1018. A series of tests from March to October demonstrated that a biotype, designated ENT A, was capable of surviving and reproducing on three of the eight parent clones of the aphid-resistant nondormant variety Moapa. The new biotype did not show a similar reaction to five other Moapa parent clones tested or to any of the five parent clones of Lahontan, a variety also resistant to this aphid. Comparisons were made with a standard working culture of the aphid, designated ENT B, originated and maintained at Bakersfield, California. In a cage test of Moapa as a variety grown from breeder seed, biotype ENT A produced much higher populations but plant mortality was not increased. Little damage to Moapa should occur unless or until biotype ENT A becomes dominant in the aphid population of an area. Even so, populations on Moapa can be expected to be much lower than those that develop on susceptible varieties