Bioinsecticidal Activity of Eucalyptol and 1R-Alpha-Pinene Rich Acetonic Oils of Eucalyptus saligna on Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae)

Abstract

Exploration of plants, animals, microbes and their products for green pesticides have been the mainstay of modern agriculturalists. Plant bioactive oils have been utilized in formulation of green pesticides, which are less toxic, least deleterious on biocontrol agents, readily biodegraded and have no or few ecological effects as compared to synthetic equivalents. This study evaluated the bioinsecticidal activity of Eucalyptol and 1R-Alpha-Pinene rich acetonic essential oils of dry leaves of the Sydney Blue gum (Eucalyptus saligna Smith) on common granivorous maize weevil. Fresh leaves of Eucalyptus saligna were harvested and the essential oils extracted from its dry powder by hydrodistillation. The chemical composition of the essential oil was analyzed by tandem GC/MS. Twelve components were identified, and the main components were Eucalyptol (34.36%) and 1R-alpha pinene (17.92%). Acetonic essential oils of 2µL, 4µL, 6µL and 8µL in 1ml acetone were used in contact toxicity, fumigant and repellent bioassays. In contact toxicity, 8µL/ml oil exerted a rapid effect on the weevils giving 100% mortality in the first day of exposure; 6µL/ml achieved 100% mortality 96 hours after treatment. Both fumigant and repellent activities showed a gradual increase in insect mortality and repellency with time of exposure as the concentrations of the essential oils were increased; 100% repellency was achieved at 8µL in the second hour and this remained constant with time. The lowest repellency of 20% was obtained at 2µL. In fumigant toxicity, the highest mortality was 70% recorded at 8µL on the third day of exposure. The results indicated that the acetonic essential oil of dry Eucalyptol and 1R-Alpha-Pinene rich Eucalyptus saligna leaves can be developed into a bioinsecticide for controlling maize weevil as a repellent, toxicant and fumigant candidate.