Rhynchophorus palmarum (L.) (Coleoptera: Dryophthoridae) is an important pest in oil palm plantations, and its populations are monitored through rhynchophorol pheromone-baited traps. To optimize the release of rhynchophorol in high-density polyethylene diffusers, five calibers (2, 3, 4, 5, and 6) were evaluated. The experiment was conducted under a completely randomized design with 15 repetitions, recording daily weight loss of pheromones. Release rate of pheromone under laboratory conditions (30.2 ± 0.1°C; 70.8 ± 0.8% relative humidity [RH]) varied between 2.2 and 10.4 mg/day. Three diffusers with 2.4 ± 0.4, 3.6 ± 0.9, and 8.5 ± 1.3 mg/day of release rates, were selected for testing in three palm-growing zones. Adults of R. palmarum captured in traps with different diffusers were counted as well as pheromone weight loss. In two of three plantations, statistical differences were found in the capture of R. palmarum adults among the diffusers that presented different pheromone release rates (Eastern: F = 8.27; df = 2, 9; P = 0.0028; Central: F = 10.79; df = 2, 9; P = 0.0008; Southwestern F= 2.20; df = 2, 9; P= 0.1402). The diffuser with the release rate of 2.4 mg/day was selected because, after remaining 4 mo in the field, the traps with this diffuser registered catches statistically equal to those that had traps with newly installed diffusers. We concluded that the release rate of the pheromone of 2.4 mg/day is optimal for the capture of adults of R. palmarum during a period of 4 mo.