The result indicated the existence of germacrone might be one of the key elements which affected the contact toxicity of R. thymifolium essential oil against T. castaneum. The contact activity of the essential oil was at a same level as that of the positive insecticide, pyrethrins (LD50 = 18.72 μg/cm2) (Yang et al., 2014) against L. bostrychophila. The compounds showed contact toxicity against L. bostrychophila (Table 4).