Bioactive compounds from Withania somnifera dun and their toxicity against some piercing sucking pests

Piercing sucking pests are destructive to many strategic crops all over the world. Botanical pesticides can be used to control these pests. A new withanolide derivative 3 named sominone A ((20R,22R)-1α,3β,20,27-tetrahydroxywitha-5,24-dienolide) was isolated from the alkaloid fraction of the whole plant of Withania somnifera. In addition, there are three known compounds named withasomine 1, methyl isoferulate 2, and coagulin Q 4 were also isolated. The structures of isolated compounds were identified using different spectroscopic methods such as 1D, 2D NMR, and HRESIMS spectroscopy. The alkaloid fraction and the four isolated compounds were tested for their pesticidal activity against four piercing sucking pests (Aphis craccivora Koch, Bemisia tabaci Gennadius, Nezara viridula Linnaeus, and Tetranychus urticae Koch) that attack many strategic crops under laboratory conditions, along with azadirachtin (Okios 3.2% EC) as a positive control. The results showed that the alkaloid compound (withasomine 1) was the most toxic to A. craccivora, B. tabaci, N. viridula, and T. urticae, with LC₅₀ values of 15.44, 36.61, 85.11, and 128.28 ppm, respectively, compared with the control. Withanolide compounds had moderate effects on all tested pests. Biochemical parameters of six enzymes; α-esterase, β-esterase, chitinase, acetylcholinesterase, glutathione-S-transferase, and peroxidase of A. craccivora were estimated at the LC₅₀ value of the most potent compound, withasomine 1 and the values were 38.83, 72.86, 31.45, 506.4, 2.62, and 251.0, respectively. The results demonstrated that all enzymes activity levels were increased compared with the control except a remarkable inhibition in AChE enzyme level was observed compared with control. Therefore, the alkaloid fraction of W. somnifera is a promising extract that contains many active compounds that can be used as a natural pesticide against many harmful pests in agriculture crops.

Graphical Abstract