1. Preparation of clove extract and oil
Dried clove (S. aromaticum) was crushed into a fine powder using Hammer-Miller (I.L.E Ltd., India). One percent (1000 mg l)of the extract was prepared using distilled water boiled at 80 °C for 20 min and filtered through a 150 μm filter paper. Desired concentrations were prepared from this extract and used for the experiments. The excess of clove extract was stored in a refrigerator at 4 °C further use. Commercially available clove oil (Sigma Aldrich Co. USA) was mixed few min prior to the experiment with ethanol 1:9 for stock solution of 100 mg/l. Aliquots from the stock solution were used for the preferred experimental concentration (Chanseau et al., 2002).