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

Caterpillars of moths and butterflies represent some of the most destructive agricultural pests and have become increasingly resistant to synthetic chemical insecticides. Manuka essential oil is known to be a potent alternative to synthetic insecticides, but its potential to control caterpillar pests remains underexplored. We evaluated the toxicity of manuka essential oil and its components against third-instar larvae of Trichoplusia ni and Chrysodeixis includens. We also evaluated their potential phytotoxic effects against cabbage, soybean, and corn.

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. Gas chromatography-mass spectrometry 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, whereas leptospermone, isoleptospermone and grandiflorone, a triketone of manuka leaves, were more toxic to both caterpillar species than the whole essential oil. The median lethal dose (LD₅₀) values (μg/larva) for manuka essential oil, fraction 2, leptospermone, isoleptospermone, flavesone, and grandiflorone against T. ni were 50, 25, 20, 20, 45 and 18, respectively and 42, 32, 28, 20, 41, and 14, respectively against C. includens. Manuka essential oil and its constituents 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 biopesticides, but improved delivery systems are needed to reduce phytotoxicity. Published 2026. This article is a U.S. Government work and is in the public domain in the USA.