Essential oils obtained from Gomortega keule, Laurelia sempervirens, Origanum vulgare, Eucalyptus globulus, and Thymus vulgaris were analyzed by gas chromatography and gas chromatography-mass spectrometry and evaluated for their toxicity against adults of Sitophilus zeamais (Motschulky) and Acanthoscelides obtectus (Say) (Coleóptera). Contact toxicity was assayed by impregnating filter paper discs with the oils. The amount of essential oils applied in each desiccator (4 1 capacity) was 4, 8, 16, or 32 ul, corresponding to 1, 2, 4, or 8 fj.1/1 air. The results showed significant differences between the tested dosages and exposure periods of the essential oils. Although desirable insecticidal activities against A obtectus were achieved with the essential oils of all five plants, the oils from G. keule and L. sempervirens were the most effective at 96 h. On the other hand, the essential oils of E. globulus and T. vulgaris were most effective against S. zeamais. In all plant species, higher doses or longer exposure periods were more effective against both insects. No mortality was observed in the control group (acetone only) of each species. Therefore, these results suggest that essential oils from the studied plants may be used against insect pests in grain storage