Efficacy of bottle gourd (Lagenaria siceraria) leaf extract in protecting against cabbage looper (Trichoplusia ni) (Lepidoptera: Noctuidae) infestation

Cabbage (Brassica oleracea L.) crops are frequently attacked by cabbage looper larvae (Trichoplusia ni), which severely reduce cabbage production. This experiment was conducted in the late spring crop season from April 15, 2024, to August 20, 2024, at the Field Science Center for the Northern Biosphere, Hokkaido University, Japan. In this study, the efficacy of an ethanolic extract of bottle gourd (Lagenaria siceraria (Molina) Standl.) leaves was compared with those of the chemical insecticide permethrin 3.2 EC and aqueous dimethyl sulfoxide (DMSO; the control). The experiment was carried out using a randomized complete block design in which each treatment comprised three replications consisting of 24 plants in total. Compared with the control, the bottle gourd leaf extract had high biopesticide activity against cabbage looper, increasing the cabbage yield by 15.98%. The yield was almost equal to that achieved with Permethrin 3.2 EC. Compared with the control, the application of the extract significantly decreased looper larval infestation in field-grown cabbage by 41.18%, 39.71%, 52.08%, and 37.96% at the fifth, sixth, seventh, and eighth weeks, respectively. Five possible biopesticide compounds, namely, apigenin-7-O-glucoside, indole-3-butyric acid, strychnine, phytol and hexadecanoic acid, were identified in the ethanolic extracts of bottle gourd leaves by liquid chromatography-mass spectrometry analysis. Bottle gourd leaf extract has potential as an environmentally friendly and sustainable alternative to toxic chemical pesticides for controlling cabbage looper infestation.