Exploration of bioactive molecules from Sesbania grandiflora (L.): identification of squalene as an effective compound against the two-spotted spider mite, Tetranychus urticae Koch, through molecular docking.

Abstract

Two-spotted spider mite (TSSM), Tetranychus urticae Koch is a devastating polyphagous mite causing considerable economic loss. Acaricides are showered in crops to manage this pest. The pest is known for developing resistance to several classical acaricides. The study was aimed at the exploration of botanical acaricide for the management of TSSM, T. urticae. Adulticidal action of ethyl acetate, ethanol and water extracts of leaves of Sesbania grandiflora (Fabaceae) were tested on T. urticae. The results showed that ethyl acetate extract showed the maximum mite mortality of 94.44 per cent, followed by ethanol extract at 87.78 per cent at 5 per cent concentration. LC₅₀ of ethyl acetate and ethanol extracts were 1.00 and 4.19 per cent, respectively. The aqueous extract gave 94.44 per cent mortality at a very high concentration of 15% with LC₅₀ of 8.57%. Molecules from the GC-MS analysis of S. grandiflora ethyl acetate leaf extract were subjected to molecular docking using acetylcholine esterase as the target molecule. The major phytomolecules identified in the ethyl acetate leaf extract of S. grandiflora were stigmasterol (15.45%), phytol (13.60%), beta-amyrone (8.72%), and squalene (7.51%). Squalene, a biomolecule with the lowest binding energy was selected from the docking result. The toxicity of squalene was evident from the fact that it caused 81.11, 85.55 and 87.78 per cent mortality at 1800, 2000 and 2200 ppm, respectively at 48 h after treatment. After, 72 h, 100 per cent mortality was recorded at 1800 ppm. This study reveals that squalene can be formulated and used as the best alternative to tackle T. urticae.