Insecticidal and Larvicidal Activities of the Acetone Extract, Fractions, and Volatile Compounds of Dennettia tripetala (G. Baker) Seeds, and Anticholinesterase Activity of the Identified Compounds

The plant, Dennettia tripetala (G. Baker), is renowned for its insecticidal potential. This study aimed to isolate insecticidal and larvicidal compounds from its seeds and to explore their possible mechanism of action. Bioassay-guided fractionation of the acetone extract, tested against adult Rhyzopertha dominica (F.), Sitophilus oryzae (L.), and 3rd instar larvae of Aedes aegypti (L.), yielded 1-nitro-2-phenylethane (NPE), nerolidol, and linalool. Gas Chromatography–Mass Spectrometry revealed the components of the most active fraction and a selected active subfraction, while Column Chromatography and High-Performance Liquid Chromatography were employed for isolation. Electron Ionisation-Mass Spectrometry, Nuclear Magnetic Resonance, and Fourier Transform-Infrared Spectroscopy confirmed all structures. NPE was the predominant compound (83.8%) in the hexane fraction and showed strong activity against R. dominica (LD₅₀: 44.93 ± 0.00 µg/cm²) and S. oryzae (68.24 ± 0.87 µg/cm²); however, it was inactive against A. aegypti larvae at 200 ppm. Nerolidol showed no activity, but a synergistic larvicidal effect emerged in the second hexane subfraction. Linalool, being highly volatile, was not further assayed. None of the compounds inhibited acetylcholinesterase at 0.5 mM, suggesting that NPE acts via a non-cholinergic mechanism. These findings establish NPE as the major insecticidal principle of D. tripetala seeds and reveal novel synergistic interactions among its constituents. The results underscore the capacity of this plant’s volatile components in developing eco-friendly insecticides, offering prospects for safer pest management strategies.