Larvae of the banded sunflower moth, Cochylis hospes, feed and develop within seeds of cultivated sunflowers in the northern Great Plains of the United States and Canada. This research was designed to delineate larval damage to sunflower seeds from known adult populations and develop an economic injury level (EIL) for C. hospes using field and cage studies. Calculations showed that with aerial application costs of $17.30/ha, a sunflower market price of $0.20lkg, and a plant population of 44,6001ha, the EIL was 5.9 larvae per head. A decision of whether economic damage is likely to occur is based on known populations of adult moths. The regression equation ( Y = 1.69 +23.93X) predicted a final number of mature lawae (Y) based on the average number of adults per 10 plants during daylight hours in July (X) from 1983-1985 and 1988-1989. A density of 1 adult per 56 plants resulted in an EIL of 5.9 larvae per head. Treatment is directed at larvae and is most effective when applications are made at the R5.1 sunflower growth stage. In 1990, cages infested with one adult per plant resulted in 9.3 larvae per head; cages infested with 10 adults per plant produced 55.2 mature larvae per head. The number of mature seeds damaged by feeding larvae varied from 59.6 seeds per plant. in cages with infested with 1 adult per plant, 294.3 damaged seeds per plant, and in cages with 10 adults per plant. Results were similar in 1991. The regression equation to predict mature larvae per head (Y) was based on adult infestation level (X), which was Y:7.34 + 4.60X. Thus, each adult results in L1.94 mature larvae per head. Each lawa destroyed 6.1 and 4.8 mature seeds in 1990 and 1991, respectively.