Abstract

Leaves of Ritchiea reflexa (Thonn.) Gilg & Benedict and aerial parts of Ctenium elegans (Kunth, 1829) were steam distillated to obtain their respective essential oils. Gas chromatography-mass spectrometry was used to characterize essential oil components. The susceptibility of these volatile oils on Amitermes evuncifer (Silvestri, 1912) was tested using contact test with washer of filter paper inside Petri dish. Twenty (20) workers of A. evuncifer were put in contact with 4 different doses of each tested essential oil. The doses were compared to two controls (negative and positive). The mortality of termites was recorded daily until the death of the last individual. GC-MS data showed that R. reflexa oils contained 3 components while that of C. elegans contained 14 compounds. Benzyl cyanide (> 80%), Benzyl isothiocyanate (> 4%), and Diisooctyl phthalate (8.98%) were the three components in R. reflexa essential oils. α-Cadinol (21.43%), Elemol (16.27%), Methyl (2Z)-3-(2,2,6-trimethyl-5-oxo-7-oxabicyclo[4.1.0]hept-1-yl)-2-propenoate (10.67%), δ-Cadinene (8.46%), and τ-Muurolol (7.56%) were the main components of C. elegans essential oil. Oxygenated sesquiterpenes (58.6%) and sesquiterpene hydrocarbons (24.55%) were then the two main groups of volatile oil components of C. elegans. All the tested doses significantly reduced the survival duration and life expectancy of A. evuncifer in comparison to controls. However, the effect of essential oils was dose dependent: the highest doses (0.19 and 0.30 µl/cm²) killed all the termites one hour after the contact (for R. reflexa). It clearly appeared that these oils significantly affected A. evuncifer. Thus, they could be regarded as potential alternatives to synthetic chemicals.

Key words: Ritchiea reflexa, Ctenium elegans, essential oils, termidicidal activity, Amitermes evuncifer.