Chemical Composition and Bioactivity of Lippia adoensis Hochst ex. Walp (Verneneaceae) Leaf Essential Oil Against Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae)

Essential oil (EO) of Nigeria-grown Lippia adoensis leaf was analyzed using gas chromatography mass spectrometry (GCMS) and its fumigant and repellent properties against Callosobruchus maculatus were evaluated. Sixteen compounds predominated by monoterpenes were identified. The major compounds were Eucalyptol (28.36%), α-Terpineol (25.99%), γ-Terpinene (15.24%), α-Pinene (5.08%), 1H-Cyclopropa[a]naphthalene (4.25%) and 1, 3, 6, 10-Dodecatetraene (3.74%). Percentage mortality due to fumigant toxicity was dose- and exposure period-dependent. One hour after treatment (HAT), application of L. adoensis leaf EO at 107 μL · L⁻¹ air caused significantly (p<0.05) higher mortality (50.00%) than 0.00% mortality observed at 0–53 μL · L⁻¹ air, but not significantly (p<0.05) different from 22.50% observed in 80 μL · L⁻¹ air. At 3 HAT, application of L. adoensis EO at 80 μL · L⁻¹ air caused significantly higher mortality (90.00 %) than mortality observed at 0 μL · L⁻¹ air. At 6 HAT, application of L. adoensis EO at 53–107 μL · L⁻¹ air caused significantly higher mortality (100.00 %) than that was observed in the control. The same trend was observed at 12 HAT where 100 % mortality observed in 27–107 μL · L⁻¹ air was significantly greater than 13.33 % observed in the control. At 3 HAT, percentage repellence was significantly (p<0.05) affected by doses. Application of EO at 10–30 μL · cm⁻² caused class V repellence (86.67%–100%) compared with the control which caused class I repellence (0–20%).