A study of the association betweenMelanoplus occidentalis(Thomas) and the prickly pear cactus,Opuntia polyacanthaHaw., was conducted on native rangeland in southeastern Wyoming. During the study, the grasshopper population density was 14.5 ± 3.7 m-2, of which 52% were M.occidentalisin cactus patches and 16%were M.occidentalisin the surrounding rangeland. Surveys of prickly pear flowers showed that 54% of the flowers had one or more (up to four) grasshoppers, of which 96% were M.occidentalis.Females of this species comprised 72% of the individuals within the cactus patches and 33% of the individuals captured in surrounding rangeland. Of the insects found in prickly pear flowers, grasshoppers accounted for 87%of the biomass; meloids (ll %)and nitidulids (2%)made up the balance. Crop content analysis of the 10 dominant grasshopper species collected from cactus patches revealed that only M.occidentalishad fed on prickly pear flowers. Within this species, 37% of all individuals had detectable levels of prickly pear cactus tissue in their crops, including 41%of the adults (58% of the females and 28% of the males) and 23% of the nymphs. Behavioral observations revealed that M.occidentalisfed on prickly pear stamens in short (10–15 min) bouts, which were frequently interrupted by aggressive physical interactions between individuals. Evaluation of the cactus stamens of flowers in the area revealed that 20% were completely or heavily damaged, 75% were moderately to slightly damaged, and 5% were undamaged by grasshopper feeding.