Essential oil of Ocimum grattissimum (Labiatae) as Sitophilus zeamais (Coleoptera: Curculionidae) protectant

Abstract

Ocimum grattissimum L. (Labiatae) leaves are widely eaten as a vegetable in Nigeria, and in the eastern parts, are traditionally used in post-harvest protection and relieving stomach aches. The effect of the essential oil of O. grattissimum leaves on Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) was assessed for repellency, mortality, progeny emergence and maize damage in the laboratory. The oil was found to be moderately repellent to the maize weevil and induced high mortality in the weevils. In addition, grains treated with the essential oil showed significant reduction in the number of progeny derived from surviving S. zeamais. There was no observable feeding damage on grains treated with the highest dosage of the essential oil extract. Gas chromatography-linked mass spectrometry (GC-MS) and GC co-injections with authentic samples showed the presence of the following major constituents: thymol (32.7%), paracymene (25.4%), -terpinene (10.8%), -selinene (4.5%), phellandrene (3.9%) and β-myrcene (3.1%). The results provide a scientific rationale for the use of the plant in post-harvest protection.