Insecticidal activity of manuka essential oil triketones against two major lepidopteran pests

Authors: Muturi, Ephantus; Neidmann, Mathew; RIBEIRO, VICTOR - Orise Fellow; Goett, Erica; Ramirez, Jose; Meepagala, Kumudini

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2025
Publication Date: 1/2/2026
Citation: Muturi, E.J., Neidmann, M.A., Ribeiro, V.P., Goett, E.J., Ramirez, J.L., Meepagala, K.M. 2026. Insecticidal activity of manuka essential oil triketones against two major lepidopteran pests. Pest Management Science. https://doi.org/10.1002/ps.70493.
DOI: https://doi.org/10.1002/ps.70493

Interpretive Summary: Every year, insect pests cause significant damage to crops in the U.S. and worldwide. Farmers often rely on synthetic chemical insecticides to control these pests, but many insect pests have become resistant to these insecticides. Therefore, there is an urgent need for new pest management products with different modes of action. Manuka essential oil, extracted from manuka plant, is known to possess insect-killing properties but its potential to control major insect pests is not well understood. This study found that manuka essential oil is toxic to the larvae of cabbage loopers and soybean loopers. The study also identified two compounds from manuka essential oil and one compound from manuka leaves that were even more toxic to these caterpillars than the oil itself. When manuka essential oil and the four compounds were applied to cabbage, soybean, and corn, they caused significant leaf damage, with cabbage and corn being the most and the least affected plants. These results demonstrate that manuka essential oil could be a promising source of bio-insecticides for controlling caterpillar pests that cause damage to crops. However, more research is needed to understand how to effectively harness manuka essential oil and its components to control insect pests without harming the plants.

Technical Abstract: The toxicity of manuka essential oil against the major insect pests remains poorly understood despite its well-documented insecticidal properties. We evaluated the toxicity of manuka essential oil and its components against third instar larvae of two major lepidopteran pests, Trichoplusia ni and Chrysodeixis includens. Manuka essential oil and its triketones were also applied to cabbage, soybean, and corn leaves to evaluate their potential phytotoxic effects. Manuka essential oil and one of its four fractions (fraction 2) were toxic to the two lepidopteran pests with fraction 2 being more toxic than the whole essential oil. GC-MS analysis revealed leptospermone, isoleptospermone, and flavesone to be the major components of fraction 2. Flavesone and manuka essential oil had similar toxicity to both caterpillar species, while leptospermone, isoleptospermone and grandiflorone, a triketone of manuka leaves, were more toxic to both caterpillar species than the whole essential oil. The LD50 values for manuka essential oil, fraction 2, leptospermone, isoleptospermone, flavesone, and grandiflorone against T. ni were 49.94, 25.08, 20.47, 19.73, 44.84 and 18.23 µg/larva, respectively. The corresponding LD50 values for C. includens were 41.97, 32.08, 28.15, 20.38, 41.00, and 14.36 µg/larva. Phytotoxicity tests revealed that manuka oil, fraction 2, and the four triketones were phytotoxic to cabbage, soybean, and corn with cabbage and corn being the most and the least affected plants, respectively. These findings demonstrate that manuka essential oil and its components are promising sources of biopesticides, but further research is needed to develop a delivery system that limits their phytotoxic effects.