The effects of the monoterpenes of 3-carene, 1,8-cineole, beta-pinene, terpinene and terpinolene on the repellent, contact toxicity of Tribolium castaneum adults and sustaining fumigant toxicity of Sitophilus zeamaise adults were examined. Monoterpene of 1,8-cineole in 20 microL mL(-1) and beta-pinene in 20 microL mL(-1) exhibited the highest percentage repellency, whereas 3-carene in concentration of 4 microL mL(-1) exhibited the significantly lower percentage repellency. Topical application and fumigant assays were used across a range of concentrations to develop dosage-mortality regressions. Among the monoterpenes tested, the most contact toxic compound was beta-pinene (with LC(50) values ranging between 31.44 and 62.07 microg mg(-1)), whereas 3-carene was the least (with LC(50) values ranging between 66.58 and 93.68 microg mg(-1)). All five monoterpenes were fumigant toxic to S. zeamaise adults, and the fumigant effect varied, along with the exposure time and the dosage. Terpinene and terpinolene were consistently the most fumigant toxic compounds on S. zeamaise, and the trend of high-to-low toxicity based on LC(50) values was not changed when treated for 24, 48, 72 and 96 h; the lethal concentration causing 50% mortality (LC(50)) with terpinolene was reduced by 71.5% after a 96 h treatment time, compared to beta-pinene and 3-carene, where only 35.0 and 31.4% reduction were observed, respectively. The data presented here indicated that the monoterpenes had repellent or toxic effects and could be screened for the control of storage pests.