Adults ofLygus hesperusKnight andL. elisusVan Duzee were mass collected from alfalfa hay fields. These insects were divided into 2 groups, each marked with a different fluorescent dust and released in adjacent cotton and alfalfa fields, respectively. Subsequent monitoring showed a rapid movement of theLygusfrom cotton to alfalfa, but the reverse was not true. This further verified thatLygusprefer alfalfa over cotton.