Chemical composition and insecticidal potential of different Origanum spp. (Lamiaceae) essential oils against four stored product pests

Abstract

This study was conducted to determine the contact and fumigant toxicity of plant essential oils extracted from four Origanum spp. against four stored product pests, Rhyzopertha dominica (F., 1792) (Coleoptera: Bostrichidae), Tribolium confusum Jacquelin Du Val, 1863 (Coleoptera: Tenebrionidae), Sitophilus granarius (L., 1875) and Sitophilus oryzae (L., 1763) (Coleoptera: Curculionidae). Chemical composition of the essential oils was determined using GC-MS. The trials were conducted under laboratory conditions in 2019 at Plant Protection Central Research Institute. Essential oils extracted from Origanum onites L. and Origanum vulgare L. var. hirtum caused 100% mortality of R. dominica and T. confusum . The computed LD50 value for O. vulgare var. verticium against R. dominica 24 h after application was 0.046 µl/insect. Single concentration fumigant study indicated that O. onites and O. vulgare var. hirtum essential oils cause high mortality (91 and 70%, respectively) of R. dominica within 24 h. Essential oils of O. vulgare showed the highest activity against R. dominica with LC50 and LC90 values of 0.0052 and 0.0144 µl/ml, respectively. The main components of O. onites essential oil were thymol (22.9%), γ-terpinene (13.0%), p-cymene (12.9%) and carvacrol (7.2%). Similarly, the essential oils of O. vulgare var. hirtum were composed of carvacrol (32.5%), thymol (16.1%), p-cymene (12.2%) and γ-terpinene (7.9%). Likewise, the essential oil of O. vulgare var. verticium had carvacrol (35.0%), p-cymene (11.6%), γ-terpinene (10.3%) and thymol (9.1%). Nonetheless, O. vulgare x O. onites essential oil had carvacrol (15.2%), cis-sabinene hydrate (14.6%), terpinen-4-ol (14.6%) and γ-terpinene (8.7%).