Chemical composition, insecticidal and repellent effects of three essential oils of aromatic plants from Cameroon: Ocimum basilicum L., Ocimum canum Sims and Ocimum gratissimum L. on Dermestes maculatus De Geer, 1774 (Coleoptera: Dermestidae)

Abstract

The main harmful insect that infest stored freshwater smoked fishes is Dermestes maculatus (De Geer, 1774) (Coleoptera: Dermestidae). To fight against this harmful insect, people used chemical pesticides. To contribute to the protection of these foodstuffs against attacks of harmful insects during storage, some essential oils of aromatic plants with insecticidal properties are considered as alternatives nowadays. The purpose of the present work was to determine the chemical composition, insecticidal and repellent effects of the essential oils of three aromatic plants of Lamiaceae: Ocimum canum, Ocimum basilicum and Ocimum gratissimum on D. maculatus. After extraction by hydrodistillation of these plants, the essential oils were analyzed by gas chromatography coupled with mass spectrometry (GC/MS). Insecticidal and insect repellent tests were carried out by contact inhalation of crude essential oils on D. maculatus isolated from stored smoked freshwater fishes. The yields of extraction revealed that O. canum (0.35%) produced more essential oils than O. gratissimum (0.30%) and O. basilicum (0.15%). The GC/MS analyzes showed 47, 46 and 41 chemical compounds in O. basilicum, O. canum and O. gratissimuum essential oil respectively with o-thymol as major active ingredient. These essential oils are rich in monoterpenes (˃75 %). The oxygenated monoterpenes are more represented in O. basilicum (80.30%) followed by O. gratissimum (66.67 %) and O. canum (60.81 %). The essential oil of O. gratissimum is the most effective with a smaller lethal dose 100 (LD₁₀₀) of 16 µL on larvae VII and 100 µL on adults, with a repellent power of 61.25% (Class IV) on larvae VII. According to the results, the lower lethal time 100 (LT₁₀₀) is from 18 h for O. gratissimum and from 22 h for O. basilicum and O. canum on the larvae VII. These results suggest a sustainable strategy for the control of insect pests in stored products.