Insecticidal activity of an isolated fraction mixture from willow bark (Salix safsaf)

The air-dried bark of safsaf tree, willow (Salix safsaf) was extracted with aqueous acetone. After the complete evaporation of acetone, some fractions were separated from the resultant extract by using partitioning between different solvent systems. One of these fractions (fraction II) was found to be biologically active. In this study it was tested for its insecticidal activity against the 4th instar of cotton leaf worm, Spodoptra littoralis (Boisd), and on the 4th instar of Culex pipiens. Fraction II exceeded its original extract on C. pipiens in its lethal effect with LCso equal 1450, 560, 240, 220 and 125 µg / ml in comparing with 2100, 1300, 1100, 500 and 130 µg / ml after 1, 2, 3, 4 and 5 days exposure and with LT50 equal 4.6, 2.1, 1.5 and < 1.0 days in comparison to 4.8, 4.2, 3.1 and 2.54 days in case of the original at 200, 500, 1000 and 1500 µg / ml. Fraction II was more effective in reducing the pupation with EC50 equal 270 µg / ml comparing to 960 µg / ml due its original extract. Although fraction II showed weak lethal effect, it exhibited a great anti-feeding activity against S. littoralis in concentration and time dependant effect with EC50 equal to 160 and 1500 µg / ml after 24 and 48 hours exposure, respectively. Based on GC-Ms analysis, this fraction appeared to be contain fatty acids; namely hexadecanoic acid (Palmitic acid, C16H32O2), octadecanoic acid (Stearic acid, C18H36O2) as saturated fatty acids and cis-oleic acid (9-Octadecenoic acid, C18H3402) as an unsaturated fatty acid as well as a flavonoid derivative of apigenin.