A series of experiments were conducted in which different 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 (a racemic mixture of the R and S isomers of methoprene) and 1 and 5-ppm S-methoprene (S-isomer only) gave 100% suppression of F 1 adult progeny of R. dominica for 24 weeks. In the second test, adult R. dominica were exposed at 27 o C and 32 o C, 57% and 75% relative humidity (r.h.) on untreated wheat and 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% to 99%, but no F 1 adult progeny were produced in treated wheat. In the final test, concentrations of 0, 0.25, 0.50, 0.75, and 1.0ppm S-methoprene EC were combined with concentrations of 0, 75, 150, 225, and 300ppm of the commercial diatomaceous earth (DE) Protect-It ( R). Within each methoprene concentration, survival generally decreased with increasing concentration of DE, and was generally greater at 75% than at 57% r.h. Only the wheat treated with 0-ppm methoprene contained an appreciable number of F 1 adults. In summary, both the dust and EC formulations of S-methoprene gave 100% suppression of F 1 adult progeny R. dominica at application rates of 1ppm, and combination treatments involving reduced rates of methoprene and DE gave effective control of R. dominica.