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Since some synthetic insecticides cause damage to human health, compounds in plants can be viable alternatives to conventional synthetic pesticides. <i>Dittrichia viscosa</i> L. is a perennial Mediterranean plant known to possess biological activities, including insecticidal properties. The chemical composition of an essential oil (EOD) from <i>D. viscosa</i>, as well as its antioxidant, antimicrobial, and insecticidal effects on the cowpea weevil (<i>Callosobruchus maculatus</i>) were determined. Forty-one volatile compounds were identified in EOD, which accounted for 97.5% of its constituents. Bornyl acetate (41%) was a major compound, followed by borneol (9.3%), α-amorphene (6.6%), and caryophyllene oxide (5.7%). EOD exhibited significant antioxidant activity in all tests performed, with an IC₅₀ of 1.30 ± 0.05 mg/mL in the DPPH test and an EC₅₀ equal to 36.0 ± 2.5 mg/mL in the FRAP assay. In the phosphor-molybdenum test, EOD results ranged from 39.81 ± 0.7 to 192.1 ± 0.8 mg AAE/g E. EOD was active on <i>E. coli</i> (9.5 ± 0.5 mm), <i>S. aureus</i> (31.0 ± 1.5 mm), <i>C. albicans</i> (20.4 ± 0.5 mm), and <i>S. cerevisiae</i> (28.0 ± 1.0 mm), with MICs ranging from 0.1 mg/mL to 3.3 mg/mL. We found that 1 µL of EOD caused 97.5 ± 5.0% insect mortality after 96 h in the inhalation test and 60.0 ± 8.3% in the ingestion assay. The median lethal concentration (LC₅₀) was 7.8 ± 0.3 μL EO/L, while the effective concentration in the ingestion test (LC₅₀) was 15.0 ± 2.1 μL EO/L. We found that 20 µL of EOD caused a reduction of more than 91% of <i>C. maculatus</i> laid eggs.