Technical Abstract: A series of experiments was conducted in which new formulations of the insect growth regulator methoprene, were evaluated for control of Rhyzopertha dominica (F.), the lesser grain borer, a major internal insect pest of stored wheat. In the first test, application rates of 10-ppm R, S methoprene and 1 and 5-ppm S-methoprene gave 100% suppression of F1 adult progeny of R. dominica for 6 months. In the second test, adult R. dominica were exposed at 27 and 32°C, 57 and 75% relative humidity (r.h.) on wheat treated with 1 to 10-ppm S-methoprene dust. Survival after a 3-week exposure decreased with increasing concentration of dust, and ranged from 69.0 to 99%, but no F1 adult progeny were produced in any treatment combination. In the final test, concentrations of 0, 0.25, 0.5, 0.75, and 1.0 ppm S-methoprene EC were combined with concentrations of 0, 75, 150, 225, and 300 ppm of the commercial diatomaceous earth (DE) Protect-It®. Only the 0-ppm methoprene treatment contained an appreciable amount of F1 adult R. dominica. Within each methoprene concentration, survival generally decreased with increasing concentration of DE, and was generally greater at 75 than at 57% r.h. In summary, both the dust and EC formulations of S-methoprene gave 100% suppression of F1 adult progeny R. dominica at application rates of 1 ppm, and combination treatments involving reduced rates of methoprene and DE gave enhanced control of R. dominica.