Volatile Compounds Emitted by <i>Ocimum basilicum</i> Repel <i>Grapholita molesta</i> , Reducing the Egg-Laying Activity and Apple Fruit Infestation Rate

<i>Grapholita molesta</i>, which causes fruit infestation damage, produces overlapping generations, making chemical control ineffective. Excessive pesticide use causes the "3R" problem, necessitating eco-friendly alternatives. Although <i>Ocimum basilicum</i> repels many pests, its effects on <i>G. molesta</i> are unclear. Olfactory, fruit infestation, and oviposition tests showed that <i>O. basilicum</i> repelled <i>G. molesta</i> and significantly reduced fruit infestation and egg laying. To identify the repellent compounds in <i>O. basilicum</i>, volatile compounds were extracted using headspace adsorption. Gas chromatography-mass spectrometry and gas chromatography-electrophysiological detection identified four key components. Electroantennogram and behavioral assays showed that 6-methylhept-5-en-2-one (10 μL/mL), 2-ethyltoluene (0.1 μL/mL), styrene (0.1 μL/mL), and ethyl carbonate (1 μL/mL) mediated the repellent effect, significantly reducing <i>G. molesta</i> fruit infestation and egg production. 6-Methylhept-5-en-2-one was most effective, decreasing fruit infestation in the field and lab and total egg production. This study reveals the repellent mechanism of <i>O. basilicum</i> volatiles, supporting plant-based repellent development for sustainable pest control.