Although phosphides are utilized in stored pest control, efforts have been made to discover environmentally friendly insecticides. For insecticidal properties, essential oils (EOs) are considered to be novel alternatives for pesticide use. This study characterized the Origanum vulgare EO by gas chromatography–flame ionization detector (GC–FID) × gas chromatography–mass spectrometry (GC–MS) and assessed the insecticidal activities against Sitophilus granarius. Mortality, post-exposure survival, behavior, and respiration caused by this EO in S. granarius were investigated. The majority of the compounds were p-cymene, carvacrol, linalool, and thymol. In dose–mortality bioassays, the lethality of this EO (LDsub.50 = 3.05 µg insectsup.−1 and LDsub.90 = 10.02 µg insectsup.−1) was confirmed in S. granarius. The survival rate was 99.9% in adults not treated with O. vulgare EOs, reducing to 44.9% and 10.3% in weevils treated with 3.05 µg insectsup.−1 and 10.02 µg insectsup.−1, respectively. The O. vulgare EO alters the behavioral pattern in terms of walking distance and resting time, displaying repellency. Additionally, this EO reduced the gas exchange of weevils from 2.78 to 2.36 µL COsub.2 hsup.−1 at 3.05 µg insectsup.−1, after 3 h EO exposure. The results suggest that O. vulgare EOs affect different biological functions in the insect, and open new perspectives for controlling stored pests, representing a first step in the innovation of green pesticides.