Despite numerous studies examining feeding injury to cotton (Gossypium spp.) caused by different stages of Lygus hesperus Knight, no consistent trends are apparent. One explanation for inconsistencies among previous results is failure to account for important sources of biological variation. Because it was only recently recognized that feeding behavior and injury differed among adults of different physiological ages, this source of variance was not controlled in earlier studies of Lygus stage-dependent injury. We incorporated this knowledge into video assays and greenhouse experiments to compare feeding behaviors, within-plant distributions, and injury to cotton plants among L. hesperus nymphs and prereproductive adults. Laboratory behavior assays indicated third instars exhibited more stylet-probes, but of shorter duration, compared with prereproductive adults. Numbers and duration of stylet-probes by fifth instars were intermediate to those of third instars and adults. Total time spent stylet-probing was similar among the insect age-classes. On whole plants, third instars tended to reside within the bracts of squares (flower buds) >3 mm in diameter, whereas fifth instars and adults tended to frequent the plant terminals. Adults were more likely than third or fifth instars to be located off the plants at any given observation. Plants exposed to fifth instars exhibited more square abscission and retained fewer squares 3–6 mm in diameter than did plants exposed to third instars or adults. Our results indicated that fifth instars were more injurious to cotton than third instars or prereproductive adults, and that differences in feeding injury corresponded with within-plant distributions exhibited by different L. hesperus age-classes.