Behavioral Selectivity: Species-Specific Effects of Nutmeg, Cinnamon, and Clove Essential Oils on Sitophilus oryzae and Its Parasitoid Lariophagus distinguendus

The integration of essential oils (EOs) with biological control agents offers a promising alternative to synthetic pesticides, though compatibility remains unclear. This study evaluated nutmeg (<i>Myristica fragrans</i>, NM), cinnamon (<i>Cinnamomum verum</i>, CIN), and clove (<i>Syzygium aromaticum</i>, CL) specifically on <i>S. oryzae</i> and <i>L. distinguendus</i>. Olfactory and behavioral responses to whole EOs and major constituents (myristicin, cinnamaldehyde, eugenol) were analyzed using the area preference method (APM) and two-choice behavioral bioassay (TCB), with confirmation by gas chromatography-mass spectrometry (GC-MS). In <i>S. oryzae</i>, APM showed attraction to all three EOs (PI = 0.14 to 0.56). A paradox emerged, however, as single constituents were mostly repellent (eugenol: PI = -0.58 to -0.70; cinnamaldehyde: PI shifted from 0.16 to -0.20), underscoring the complexity of EO mixtures where multiple compounds act jointly rather than individually. In contrast, <i>L. distinguendus</i> strongly avoided CL and CIN in TCB, with fewer than 30% of parasitoids choosing the EO-treated side (χ² test, <i>p</i> < 0.05). CIN therefore demonstrated selective potential, simultaneously attracting <i>S. oryzae</i> while repelling <i>L. distinguendus</i>. These findings highlight the dual role of EOs as botanical pest control tools, while stressing the need to consider non-target effects before practical application.