Oregano oil

Acyclovir was purchased from Acros Organics, Morris Plains, NJ, USA. Tea tree oil, garlic oil, peppermint oil, sandalwood oil, anise oil, oregano oil, chamomile oil, lemon palm oil, thyme oil, and eucalyptus oil were procured from Sigma Aldrich, St. Louis, MO, USA. Oleic acid, PEG 200^®, PEG 400^®, Labrasol^® Propylene Glycol^® and Transcutol^®, Tween80^®, span80^®, tween60^®, span60^®, tween20^®, span20^®, hydroxyl propyl cellulose, and silicone were purchased from Gattefosse (Saint Priest Cedex, France). The chemicals used in the study consisted of analytical grade.

Organic corn grains were purchased from Great River Organic Milling (Arcadia, WI, USA). The maize weevil, S. zeamais, was kindly provided by Dr. Beatrice Dingha’s Lab at North Carolina A&T State University. Six essential oils (EOs) (including thyme oil, oregano oil, cinnamon oil, clove oil, eugenol, and orange terpenes) and dimethyl sulfoxide (DMSO) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Pirimiphos-methyl, an insecticide specifically for fumigation of corn storage facility in the United States, was also purchased from Sigma-Aldrich and used as positive control, while 10% DMSO in deionized water was used to dilute EOs and served as negative control. Wide mouth clear glass jars (60 mL) with screw caps, Mason jars (1 L), glass serological pipets, disposable pipette tips, and cotton balls were purchased from Fisher Scientific (Suwanee, GA, USA).