ABSTRACT

The insecticidal activity of essential oils from Cassia occidentalis and Euphorbia milii leaves on Periplaneta americana, Tettigonia virridissima and Anopheles gambaie were analysed. The essential oils were extracted by steam distillation and using Soxhlet apparatus. Test insects were exposed to oils at 3 dose levels (200mg, 400mg and 600mg) kg/bw for 24 hours. Mortality measurements and biochemical evaluation for changes in ionic composition and toxicity markers in fat bodies and haemolymph were carried out. DNA from test insects were analysed using Random Amplified Polymorphic DNA Polymerase Chain Reaction (RAPD-PCR) to determine the level of genotoxicity induced by the oils. The effect of oils on biochemical indicators of toxicity was evaluated in Wistar rats administered 1500mg/kg bw, 3000mg/kg bw and 5000mg/kg bw for 14 days. Sex hormones, haematological, liver and kidney function indices were determined. Proximate and mineral analysis of plants, as well as GC-MS chemical profile of essential oils were evaluated. The results showed contact insecticidal activity of E. milii oil at LD50 and LD90 as 0.583 and 1.108 for P. americana, 0.681 and 1.215 for T.virridisima and 0.488 and 0.893 for Anopheles gambaie, respectively. C. occidentalis oils showed insecticidal activity of 0.889 and 1.689 for P. americana, 1.013 and 1.973 for T. virrdissima, and 0.722 and 1.847 for Anopheles gambaiae, respectively. The corresponding values for the conventional insecticide, SWAN were 0.417 and 1.017 for P. americana, 0.607 and 1.111 for T. virridissima and 0.40 and 0.743 for A. gambaiae, respectively. The results of ionic composition showed significant (p < 0.05) decrease in Mg2+ and Na+ in fat bodies of insects exposed to E. milii oil. On the other hand C. occidentalis oil caused significant(p < 0.05) decreases in acetylcholinesterase activity, Mg2+ and K+ , and increased glutathione-S-transeferase activity, protein and Mn2+ concentrations. E.milii and C.occidentalis also induced 68% and 31% polymorphism respectively with chi 15 and EZ oligonucleotide primers, on insects’ DNA. The result of the toxicity study in rats showed no significant (p >0.05) effect on measured indices implying that the oils were safe within the doses studied. Proximate analyses of plant leaves revealed the presence of carbohydrates 74.16±1.07, 67.9±0.38, proteins 4.98±0.25, 3.80±0.03, ash 3.01±0.04, 5.00±0.02, moisture 15.3H0.27, 9.50±1.71 and fat 2.54±0.30, 13.8±0.19 for E.milii and C.occidentalis respectively. Mineral analysis revealed the presence of: calcium 2.87±0.8, 2.95±0.35, potassium1.94±0.06, 2.05±0.14, magnesium 1.21±0.19, 1.32±0.03, phosphorus 1.02±0.19, 0.54±0.05 and sodium 0.52±0.02, 0.43±0.06 in E.milii and C.occidentalis respectively. The GC-MS analysis of the essential oils revealed the presence of d-limonene, 1, 2- benzenedicarboxylic acid bis 2-methylpropyl ester, phthalic acid di (oct-3-yl) ester, hexadecanoic acid,2 hydroxy-1-(hydroxymethyl) ethyl ester , 6, 9,12,15-docosatetraenic acid methyl ester for E.milii and Phthalic acid isobutyl octyl ester, hexadecanoic acid methyl ester, 9,12-octadecadienoic acid methyl ester, 9-octadecenoic acid (z)- methyl ester, methyl stearate, phthalic acid,2-ethylhexyl isohexyl eter, decane, oleic acid, 4,7,- methano-lh-indene,3a,4,7,7a-tetrahydro and n-hexadecanoic acid for C. occidentalis. Overall, data from this study provides strong evidence to show that essential oils from E.milii and C. occidental'^ possess bioactive secondary metabolites with commendable degrees of insecticidal efficacy and may be safe to non-target species.