Insecticidal Activity of Essential Oils Obtained from Piper nigrum and Psoralea corylifolia Seeds against Agricultural Pests

The insecticidal activity of essential oils obtained from methanol extracts of Piper nigrum L. (Piperaceae) and Psoralea corylifolia (Fabaceae) against Epilachna insect and Mustard aphids (Lipaphis erysimi) was investigated in a series of laboratory experiments. Insecticidal activity was determined at 25 ± 4°C and 70 ± 5% R.H., in dark conditions. The methanol extracts of the dried seeds of the plants were subjected to hydrodistillation using a Clevenger type apparatus. The major components in these essential oils are identified using GC-MS spectroscopy and their insecticidal activity was tested. The predominant components in the oil of Piper nigrum are Methyl benzene, deltaelemene, alpha-copane, caryophyllene, alpha caryophyllene, beta bisabolene and delta cadinene where as the predominant components in the oil of Psoralea corylifolia are toluene, alpha-pinene, L-beta-pinene, beta-pinene, 3carene, limonene, Gamma terpinene, terpinolene, alpha santolina alcohol, 4-terpineol, Cyclohexene, 1-methyl-4-(1-methyl ethenyl), caryophyllene, alpha caryophyllene, thumbergene. The mortality rate of the agricultural pests was checked against 1%, 5% and 10% conc. of essential oil. The essential oil from Psoralea corylifolia and Piper nigrum shows strong toxic effect against Epilachna insect where as that from Psoralea corylifolia and Piper nigrum were significantly less effective against Mustard aphids (Lipaphis erysimi). Finding insecticidal activity is of great importance as using plant extracts as insecticides, are biodegrable and do not leave toxic residues.