Feeding injury to cotton squares and bolls by Lygus hesperus nymphs and adults was evaluated in a three-part study for Bt cotton (DP 499 BR) during 2005 in New Mexico. Comparative feeding studies were performed using 4th instar nymphs, 5th instar nymphs, and adults. Field-collected Lygus from alfalfa were identified to species and stadium, and starved for 24 hrs before they were transferred to cages. In the first experiment, the bugs were caged on whole plants at different densities (0, 1, 2, 3, 4, 6, 8, and 10) each in a completely randomized design and allowed to feed for one week before removal. Cages remained on the plants until plant maturity. At harvest, plants will be mapped, bolls hand-harvested, and yield and quality will be determined. The second and third experiments assessed the impact of Lygus on individual squares and young bolls. Two sizes of squares (pinhead and matchhead) of known age and bolls (1-2 day and 7-8 day) were used for these experiments. In a randomized block design, an individual Lygus nymphs or adult was caged on squares or bolls for a 48-hr feeding period. One-half of the squares and bolls were removed and evaluated for external and internal signs of feeding, and the remaining one-half were allowed to develop to maturity. The latter will be weighed and quality assessed. The goals of this research are to better describe plant bug feeding injury on known ages of squares and bolls and to develop an economic injury level for L. hesperus on cotton in New Mexico.