The team, led by Mst. Samia Sultana of Hokkaido University’s Graduate School of Agriculture, ran their trial during the late spring season from April 15 to August 20, 2024, at the university’s Field Science Center for the Northern Biosphere in Hokkaido. They grew the popular Japanese cabbage variety ‘Kinkei-201’ in a randomized complete block design, with each of three treatments replicated three times across plots of 24 plants. One group of plants was sprayed with the bottle gourd leaf extract dissolved in dilute dimethyl sulfoxide, a second received the chemical insecticide permethrin 3.2 EC as a positive control, and a third received only the aqueous DMSO carrier as a negative control. Spraying began ten days after transplanting and continued at seven-day intervals until the end of the growing season, for a total of eight applications at ten milliliters per plant.

The results were striking. Compared with the untreated control, the bottle gourd extract reduced looper larval infestation by 41.18 percent in the fifth week, 39.71 percent in the sixth, 52.08 percent in the seventh, and 37.96 percent in the eighth week of monitoring. Permethrin still delivered the strongest protection overall, but the botanical extract was not far behind where it mattered most: at the harvest. The extract-treated plots produced 48.26 metric tons of cabbage per hectare, essentially identical to the 48.23 metric tons per hectare achieved with permethrin, while the control plots yielded only 41.61 metric tons per hectare. That difference translates to a 15.98 percent yield increase over the control, driven almost entirely by the extract’s ability to keep hungry caterpillars at bay.

The cabbage looper earns its ominous name from the looping gait of its caterpillars, which arch their bodies as they crawl across leaf surfaces. It is among the most troublesome pests of cruciferous crops worldwide, and it is most damaging once cabbage enters the heading stage, when larvae chew through the undersides of leaves and burrow into the developing head. A single female moth can lay between 300 and 600 eggs over roughly ten to twelve days, and in warm conditions the insect can complete its entire life cycle from egg to adult in as little as 18 to 25 days. Mature larvae are voracious, eventually consuming up to three times their body weight in plant tissue each day. During the Hokkaido trial, the looper was the only pest present in meaningful numbers, making it an ideal target for a controlled comparison of treatments.

Preparing the extract was a straightforward affair that farmers in many regions could plausibly replicate. The researchers collected bottle gourd leaves on the Hokkaido University campus, discarded any damaged or discolored samples, and dried the rest at room temperature before grinding them into a powder. Roughly 100 grams of powder was soaked in 400 milliliters of ethanol and shaken for 74 hours in a constant-temperature incubator, after which the mixture was centrifuged, filtered, and evaporated at 50 degrees Celsius to yield a crude extract. One gram of this extract was dissolved in one milliliter of DMSO and diluted into a liter of distilled water for spraying. The choice of DMSO was deliberate: the solvent is powerful enough to carry a complex mixture of plant compounds into solution, and at concentrations below 0.1 percent it is considered safe for plants and animals.

To understand why the extract works, the team turned the crude preparation over to liquid chromatography coupled with high-resolution mass spectrometry. The analysis tentatively identified 21 chemical compounds in the ethanolic extract, five of which stand out as plausible biopesticide agents: apigenin-7-O-glucoside, indole-3-butyric acid, strychnine, phytol, and hexadecanoic acid. Apigenin-7-O-glucoside, a flavonoid, has documented insecticidal effects, killing insects, reducing their egg-laying, deterring feeding and growth, and interfering with their ability to digest plant tissue. Indole-3-butyric acid, better known as a plant growth regulator, has been used alongside other chemicals to boost plant resistance to insect attack. Phytol, a diterpene alcohol, has shown considerable promise as an eco-friendly botanical insecticide, while hexadecanoic acid, a common fatty acid, carries known nematicidal and pesticidal activity.

The presence of strychnine among the identified compounds is notable and, on its face, alarming, since the alkaloid is infamous as a rodenticide and avicide. The authors note that strychnine is also classified as an insecticide, and its detection here was tentative, based on mass-spectrometric matching rather than isolation and quantification. That caveat matters: identifying a compound in a complex plant extract does not establish how much of it is present, whether it is bioavailable to insects, or whether it contributes to the observed pest suppression. It also raises questions that any regulatory pathway would need to answer, since a biopesticide is only as acceptable as its most toxic constituent. The researchers themselves frame the compound list as a set of targets for future work rather than a finished safety profile.

Complementary Fourier transform infrared spectroscopy added a second layer of chemical characterization. The spectra revealed absorption bands consistent with primary aliphatic amines, carboxylic acids, alkanes, alcohols, sulfones, phenols, anhydrides, alkenes, and even a halo compound, painting a picture of an extract rich in the kinds of secondary metabolites that plants deploy as chemical defenses. Such compounds can disrupt insect cell membranes, inactivate enzymes, and derail metabolic processes, leading to growth inhibition or death. Notably, the extract did not appear to harm the crop itself: chlorophyll content measured by SPAD meter, photosynthesis rates, plant spread, and head diameter showed no significant differences among treatments, and extract-treated plants actually grew tallest, though not significantly so.

The broader context gives the work its urgency. Synthetic pesticides remain the backbone of pest control in intensive vegetable production, but chronic exposure has been linked in assessments to cancers, neurological and cardiovascular disease, reproductive harm, and impaired respiratory health, while agricultural chemicals contribute to documented declines in insects, birds, bats, earthworms, fish, and amphibians. Botanical biopesticides, by contrast, tend to be target-specific, sparing natural enemies of pests, and they decompose quickly in the environment, leaving minimal residues on fresh produce. Bottle gourd itself is an apt source: among the first plants ever domesticated and the only crop with a global distribution before Columbus, it is already cultivated worldwide for food and medicine, and earlier studies have shown its leaf extracts effective against cabbage aphids and mosquito larvae.

The Hokkaido team is careful to note the limits of the study. It was a small-scale field trial in a single season at a single site, and the extract’s formulation, concentration, and spray schedule were not optimized. Whether the same results hold across different climates, soil types, and pest pressures remains to be seen, as does the extract’s compatibility with integrated pest management programs and its effects on beneficial insects under real-world conditions. Still, the headline numbers are hard to ignore: a leaf extract from a plant most gardeners grow for its fruit cut looper damage nearly in half in peak weeks and matched a commercial pyrethroid on yield. If follow-up research can pin down the active compounds, standardize the formulation, and clear the safety questions, the ancient bottle gourd may find a new role as a factory for sustainable crop protection.

Subject of Research: Botanical biopesticide control of cabbage looper in cabbage using bottle gourd leaf extract

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

Article References: Sultana, M. S., Shimizu, N., Itoh, T., & Iwabuchi, K. (2025). Efficacy of bottle gourd (Lagenaria siceraria) leaf extract in protecting against cabbage looper (Trichoplusia ni) (Lepidoptera: Noctuidae) infestation. Crop Health, 3(1), Article 11. https://doi.org/10.1007/s44297-025-00050-7

Image Credits: AI Generated

DOI: 10.1007/s44297-025-00050-7

Keywords: bottle gourd, cabbage looper, biopesticide, botanical insecticide, Lagenaria siceraria, Trichoplusia ni, cabbage, LC-MS, phytochemicals, sustainable agriculture, permethrin, pest management