The spotted alfalfa aphid (yellow clover aphid on alfalfa)

The spotted alfalfa aphid, Therioaphis maculata (Buckton), has become the most serious pest of alfalfa in many parts of southwestern United States since its discovery in New Mexico early in 1954. Chiefly a pest of alfalfa, this insect also infests bur clover and sour clover. It does not live on red clover, Ladino clover, or sweetclover. This insect damages alfalfa by ruining hay crops, by slowing regrowth, by thinning stands, and by killing seedling fields. Spotted alfalfa aphid populations and resultant damage have been highest on the desert in the late fall, spring, and early summer. In cooler sections this aphid has done damage only in the summer and early fall. The use of insecticides to control the spotted alfalfa aphid has not prevented ladybird beetles from doing a good job on this aphid when conditions were right, usually when the weather was warm.