Anti-feedant activity of Pachygone laurifolia (DC.) L.Lian & Wei Wang bark extracts in tobacco cutworm, Spodoptera litura (Lepidoptera: Noctuidae) is mediated through biochemical responses and pathological damage

Spodoptera litura is a severe polyphagous insect pest, causing extensive damage to agricultural crops all over the world. The present study was undertaken to investigate the response of S. litura to polarity gradient fractions of Pachygone laurifolia bark extract. The fraction IV and V of P. laurifolia bark possess a significant anti-feedant activity and growth inhibitory effect on S. litura . The active fractions inhibited carboxylesterase activity, whereas no significant difference in total protein content was observed. Alteration in glutathione S- transferase activity and inhibition of acetylcholinesterase activity were noted on exposure of fraction V. The histopathological studies of the midgut region of the exposed larvae exhibited structural loss, damage in peritrophic membrane and longitudinal muscles, disintegration of goblet cells, oedema and lysis of the epithelial cells compared to control even at minimum concentration of exposure. Gas chromatographic – mass spectrometric analysis was carried out to ascertain the active constituents with the anti-insect properties. Overall, our findings revealed that fractions of P. laurifolia has significant anti-feedant activity mediated through biochemical mechanisms involving detoxification, oxidative stress and pathological damage. This plant extract has the potential to be developed as biopesticide formulation.