Insecticidal activity of selected plant essential oils against four major urban tree insect pests.

Abstract

Urban trees provide important ecological and aesthetic benefits but are increasingly threatened by sap-feeding and defoliating insect pests. This study evaluated the insecticidal activities of seven commercial essential oils and a supercritical carbon dioxide (SC-CO2) extract of Zanthoxylum piperitum against four major urban tree pests: Aphis gossypii, Metcalfa pruinosa, Hyphantria cunea, and Lycorma delicatula. Chemical compositions were characterized by gas chromatography-mass spectrometry, and insecticidal activity was assessed using direct-spray, concentration-mortality, and residual-contact bioassays. Dinotefuran was included as a conventional neonicotinoid reference treatment. Among the botanical materials, cinnamon essential oil consistently produced the highest mortality, while the Z. piperitum SC-CO2 extract also showed high activity. At 24 h after treatment, dinotefuran produced corrected mortalities of 52.7-83.4% across the four insect species. Probit analysis based on dead and surviving insect counts from five tested concentrations showed that cinnamon essential oil had LC50 values of 0.37-0.54% (v/v), while the Z. piperitum SC-CO2 extract had values of 0.45-0.60% (w/v); these different concentration units preclude a direct numerical potency ranking. All fitted probit models showed no significant lack of fit. Residual-contact bioassays further showed that cinnamon oil retained the greatest insecticidal activity during the 72-h residue-aging period, followed by the Z. piperitum extract. These findings support the potential of cinnamon essential oil and Z. piperitum SC-CO2 extract as botanical insecticide candidates for urban tree pest management. However, semifield and field evaluations, including phytotoxicity and effects on natural enemies, pollinators, aquatic organisms, and other nontarget species, are required before practical incorporation into integrated pest management programs.

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