Screening of Selected Medicinal and Aromatic Plants for Their Insecticidal Activity against Diamondback Moth [Plutella xylostella (L.)]

The diamondback moth, Plutella xylostella (L.) is a major pest of cruciferous vegetables, causing severe yield losses, and its rapid development of resistance to synthetic insecticides necessitates the search for eco-friendly alternatives. A laboratory screening study was conducted at the College of Horticulture, Bengaluru, to identify promising insecticidal plants from twenty medicinal and aromatic plants using seed, leaf, rhizome and other plant part extracts prepared in aqueous and methanol solvents through the leaf-dip bioassay method against early third instar larvae of P. xylostella. Among the aqueous extracts, neem seed kernel extract (NSKE) at 2.5% exhibited the highest larval mortality (93.33%) after 120 h of the treatment followed by pongamia (90.00%), turmeric (86.67%), bael and hebbevu (83.33%), datura (80.00%) and calotropis (76.67%), while jatropha and sweet flag recorded the lowest mortality (40.00%). Methanol extracts showed consistently superior insecticidal activity compared to aqueous extracts. NSKE recorded the highest larval mortality (96.67%), followed by pongamia (93.33%) and datura (86.67%) at 2.5% concentration after 120 h. Turmeric, hebbevu and cinnamon were statistically on par with mortalities of 90.00, 86.67 and 76.67%, respectively, whereas lantana and marigold were the least effective (43.33%). NSKE and pongamia treatments significantly suppressed pupation and adult emergence, indicating strong growth-regulating effects. Overall, screening of twenty medicinal and aromatic plants identified several promising botanical insecticides, with NSKE at 2.5% being the most effective, followed by pongamia and leaf extracts of datura, calotropis, bael, hebbevu and nagadali. The consistently higher efficacy of methanol extracts further indicates its superiority in extracting bioactive compounds. These plants can therefore be considered promising eco-friendly alternatives for the sustainable management of diamondback moth on cabbage and cruciferous crops.