Effects of Rosemary Essential Oil on Host Selection Behavior of Spodoptera exigua (Lepidoptera: Noctuidae) and Its Chemical Mechanisms

Abstract

The global occurrence of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) intensifies reliance on synthetic insecticides, causing resistance and ecological risks. This study investigates rosemary (Rosmarinus officinalis L.) essential oil (REO) as a sustainable alternative, examining its effects on S. exigua behaviors and chemosensory mechanisms. Gas chromatography–mass spectrometry identified 3 dominant terpenoids (α-pinene, cineole, and verbenone) and 13 minor constituents (>1%) in the essential oil. Larval bioassays showed that REO significantly inhibited larval growth and development (P < 0.001), with persistent sublethal effects on subsequent stages. It also demonstrated concentration-dependent inhibition of larval feeding. At a concentration of 2%, the selective and nonselective feeding deterrence rate reached 62.01 and 78.40% (P < 0.001), respectively. Behavioral experiments further revealed that the essential oil had a concentration-dependent dual behavioral regulatory effect in that, at a concentration of 0.005%, it attracted oviposition and olfactory orientation, whereas at concentrations ≥0.05%, it showed significant repellency. In oviposition choice tests, 2% REO achieved a 49.92% (P = 0.008) repellency rate; in Y-tube olfactometer assays, the repellency rate was 75% (P = 0.028). Molecular docking revealed β-caryophyllene and verbenone form stable hydrophobic interactions with S. exigua odorant-binding protein OBP1 and OBP7, suggesting a critical role in disrupting olfactory recognition. These results indicate REO acts as a multitarget behavioral modulator, interfering with olfaction, development, feeding, and oviposition in S. exigua, thereby providing an ecofriendly pest management option.