The repellent activity of eight compounds which were isolated from the essential oils of M. tetramera and M. kwangsiensis was also measured and results were presented in Table 5. The PR values showed that the eight compounds exhibited different levels of repellent activity against T. castaneum. The PR values of alloaromadendrene, spathulenol, caryophyllene oxide were higher than 50% and could be comparable with that of DEET at the higher concentration (>3.15 nL/cm2) and these chemical compounds were observed in most of the essential oil samples investigated. It was also found that the PR values increased with the increase of testing concentrations for each of the compounds. So the repellent activity of essential oils could be related to the existence of such chemical compounds.