Chemical Composition and Insecticidal Activity of <i>Ocimum basilicum</i> and <i>Ocimum × africanum</i> Essential Oil

Stored-product insects often necessitate the use of synthetic insecticides, which can have a negative impact on the environment. Phytochemicals, particularly essential oils (EOs), represent an ideal alternative. The EOs derived from the aerial parts of Ocimum basilicum (OB) and Ocimum × africanum (OA) were chemically characterized and assessed for their insecticidal activity against Tribolium castaneum (Coleoptera: Tenebrionidae) and Liposcelis bostrychophila (Psocoptera: Liposcelididae). The EOs were extracted from OB and OA using hydrodistillation and analyzed with gas chromatography-mass spectrometry, with estragole identified as the major constituent. Fumigation toxicity tests showed that estragole has a significant effect on both pests, with median lethal values (LC₅₀) values for T. castaneum (9.67 mg/L air) and L. bostrychophila (6.01 mg/L air) that are significantly lower than those of EOs. Contact toxicity tests indicated that the insecticidal potential of OA was superior to that of OB, with LC₅₀ values for T. castaneum (18.63 µg/adult) and L. bostrychophila (1.83 µg/adult). Repellency experiments showed that the EOs were capable of repelling the pests to differing degrees. The effectiveness of repellency was dependent on both concentration and exposure time. The results indicated that EOs of OB and OA have the potential for controlling stored-product insects.