Studies on some plant extracts and their effective chemical constituents against some pests

Abstract

Peels of fresh navel orange (citrus sinensis) and lemon (citrus limon) fruits (Rutaceae) were extracted by absolute methanol (MeOH) and n-Hexane (Hex) as solvents of different polarities.The aim was to perform some chemical and physicochemical analysis on the peel extracts for potential use as botanicals against the cotton leafworm, Spodoptera littoralis (Boisd.) . The extraction solvent type was a principal factor in determining chemical composition, and consequently physicochemical properties of the citrus extracts. MeOH proved to be significantly (P<0.01) more efficient than Hex to extract phytochemicals (proteins, carbohydrates, phenols, flavonoids and alkaloids) from lemon and orange. Also physicochemical characteristics, such as % yield and specific gravity of MeOH extracts were significantly higher than Hex extracts. However Hex extracts were more acidic than MeOH ones. Hex extracts were more toxic against of 4th larval instar the cotton leafworm, S. littoralis. It is probable that Hex more able to extract bioactive secondary metabolites than MeOH. Toxicity of citrus peel crude extracts against S. littoralis larvae was determined by the solvent used for extraction, citrus species and method of treatment. Generally, lemon extracted by Hex, used for repellency or contact action was the most efficient against the larvae.