Phytochemical analysis and toxicity of Casuarina equisetifola (whistling pine) To Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)
Eneh F U, Nwankwo E N., Okwuenu P.
Qualitative phytochemical analysis of Casuarina equisetifolia (whistling pine) leaf was carried out using three solvents; petroleum ether, ethanol and water. Subsequently, laboratory investigation was conducted on the toxicity of the leaf extracts to Sitophilus zeamais. Six concentrations of the extracts ranging from 0.625%- 20% including a control were used. Aliquot of each concentration (1.0mL) was evenly dispensed onto No. 1 Whatman filter paper in petri-dishes placed in a Completely Randomized Design (CRD). Ten unsexed active adults of S. zeamais were introduced into each petri-dish. Qualitative phytochemical analysis revealed the presence of Saponins, flavonoids, Cyanogenic glycosides and Anthracene glycosides in all extracts, while tannins were present in only ethanol and aqueous extracts. Similarly, alkaloids were present in the aqueous extract only. Results of the toxicity study showed that dosage-related mortality responses were observed after 12 hours of exposure to different extracts of the plant. Hence, mortality increased with increase in concentration of the plant. The plant extracts caused mortalities of 80%, 77.5% and 85% at highest concentrations of aqeous, ethanolic and petroleum ether respectively while the lowest concentrations caused 37.5%, 35% and 35% respectively. Statistical analysis showed that these extracts were not significantly different (P>0.742) from each other. The LD50 values of these extracts were respectively 16.81µg/ml, 18.59µg/ml and 6.07µg/ml for aqeous, ethanolic and petroleum ether. This study suggests that plant extracts of Casuarina equisetifolia could perhaps be good alternatives to synthetic pesticides which adversely affect man especially when used on food crops. It is similarlyrnsuggested that the active phytochemicals could be the saponins, flavonoids, cyanogenic glycosides or anthracine glycosides acting individually or synergistically.