Beetles- and fungi-induced volatiles from wild apple trees modulate host selection behavior of Agrilus mali (Coleoptera: Buprestidae).

Malus sieversii (Ledeb.) M. Roem. (Rosales: Rosaceae), widely recognized as the primary progenitor of Malus domestica Borkh. (Rosales: Rosaceae), is threatened by both Agrilus mali Matsumura (Coleoptera: Buprestidae) and Valsa mali Miyabe et Yamada (Diaporthales: Valsaceae) in China. Notably, A. mali adults prefer wild apple plants damaged by beetles and by fungi, yet the chemical cues driving this phenomenon remain elusive. Through gas chromatography-electroantennography (GC-EAD) and gas chromatography-mass spectrometry (GC-MS), 13 volatiles were identified from healthy, A. mali-infested, and V. mali-infected branches. The relative concentrations of cis-2-methylcyclopentan-1-ol, (Z)-3-hexenol, (Z)-3-hexenyl acetate, and decyl aldehyde in damaged branches were higher than those in healthy branches. These 4 components effectively attracted A. mali adults in Y-tube and field tests, and individual additions of cis-2-methylcyclopentan-1-ol, decyl aldehyde, or (Z)-3-hexenyl acetate to (Z)-3-hexenol increased captures compared with (Z)-3-hexenol alone, with (Z)-3-hexenyl acetate exhibiting the strongest synergistic effect. A mixture of these 4 components in equal proportions demonstrated the highest trapping capacity. In contrast, hexyl hexanoate was lower in damaged branches and repelled A. mali adults. Traps baited with lures containing this component resulted in a significant reduction in captures. Additionally, these volatiles were applied as effective attractants and repellents for A. mali adults in push-pull experiments. Behavioral and field assays demonstrated that these volatiles are involved in modulating host selection behavior of A. mali. These findings could offer an effective strategy to mitigate the combined harm caused by A. mali and V. mali, thereby preserving the ecology of wild apple forest.