Bio-efficacy of mustard seed extracts against Bihar hairy caterpillar Spilosoma obliqua (Erebidae: Lepidoptera) & assessment of mustard allelo-chemicals in response to mustard aphid Lipaphis erysimi (Aphididae: Hemiptera) infestation

Abstract

Mustard seed contains glucosinolate-myrosinase system of substrate-enzyme metabolism, accompanied with compartmentalized cells. Upon rupture, enzyme myrosinase leads to breakdown of glucosinolates and its metabolized products like allyl, benzyl, phenyl type of isothiocyantes and many other types like nitriles are released. The myrosinase activity is tested in three globally utilized different seed coat color mustards viz., brown mustard (Brassica juncea), white mustard (Sinapis alba) and black mustard (Brassica nigra) to demonstrate the release of glucosinolates which are known to deter insect pests. Aqueous seed extracts of these mustard types were subjected to anti-feedant activity analysis and oil extracted from these mustard seeds was subjected to insecticidal activity analysis against Spilosoma obliqua 4th instars on castor leaves. Meanwhile, the mustard leaves in open field were allowed for natural aphid infestation during early months from January to March. Thereafter, the leaf twigs of white, black and brown mustard, infested and uninfested by aphids, were collected and myrosinase activity of plants was analyzed with varying levels of important pest inflicted biochemicals in plant, viz., Total phenols, ortho-dihydric phenols and flavonols. Gas Chromatography–Mass Spectrometry analysis of mustard oil used in insecticidal activity was performed to elucidate the role of biochemicals involved in action. These compounds along with fatty acids and sterols compounds are known to have anti-feedant & insecticidal activities. Aqueous extract components were also subjected to total glucosinolate analysis, spectrophotometrically for knowing their concentration, with highest in brown (85.81 µmol/g) followed by black (59.32 µmol/g) and lowest in white mustard (47.63 µmol/g). The amount of glucosinolates, free fatty acids & sterol compounds present in different coat color mustard seed types are being correlated here with their potential bioactivities against biological plant pests. Bio-control of potentially harmful insect pests is possible by utilizing anti-feeding & insecticidal potential of mustard seed extracts.