Technical Abstract: The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is an important insect pest in food processing facilities. Pheromone trapping is frequently used to monitor red flour beetle populations in structures; however, the optimal trap density and the relationship between trap captures and beetle density is unknown. Two experiments were performed concurrently in environmentally controlled 30 square meter walk-in chambers to determine the relationship between pheromone trap captures of red flour beetles and beetle and trap number. In one experiment beetle density was kept constant at 200 individuals while trap number was varied from 1-8 per chamber, and in the other experiment trap number remained constant at 1 per chamber while beetle density varied from 20 to 800 individuals. Results indicated that approximately 1 out of 23 red flour beetles were captured in a trap. Number of beetles captured in traps increased significantly as beetle density increased; however, the proportion of beetles captured remained consistent across beetle densities with a mean of 4.7 ± 0.6% of individuals captured. Trap captures varied significantly with trap placement within experimental chambers, indicating that subtle differences in the trapping environment can influence trap captures. Data suggested that trap densities of 0.07 – 0.10 per square meter (2 – 3 traps per chamber) would maximize trap capture, while a trap density of 0.13 per square meter (4 traps per chamber) would maximize the predictive ability of a trapping equation estimating beetle density from trap captures. Results provide preliminary information needed to more thoroughly explore how environmental factors might influence red flour beetle trap capture in the absence of changes in beetle density. Further understanding of these relationships will allow for more accurate assessments of absolute beetle density from pheromone trap capture data.