Perilla frutescens (L.) Britton (Lamiales: Lamiaceae) cultivation repels red imported fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) through volatile organic compounds

The red imported fire ant (RIFA, Solenopsis invicta Buren) (Hymenoptera: Formicidae) is a highly destructive invasive pest that threatens agriculture, biodiversity, human health, and infrastructure worldwide. Current management heavily relies on synthetic chemical insecticides, but their widespread use has led to resistance development, environmental contamination, and restrictions in ecologically sensitive areas, necessitating sustainable and eco-friendly alternatives. Perilla frutescens (L.) Britton (Lamiales: Lamiaceae) is a multi-purpose aromatic plant valued for its essential oil and medicinal properties, but its potential against RIFA remains underexplored. Here, we evaluated the repellent effect of P. frutescens cultivation on RIFA and investigated its underlying chemical basis. Our results showed that P. frutescens -cultivated plots consistently harbored significantly fewer foraging workers than non-cultivated controls, with the strongest effect observed during the seedling stage; this repellency was independent of plant shading. Y-tube olfactometer assays demonstrated that intact P. frutescens plants repelled 78%–85% of workers within 5–20 min. P. frutescens essential oil significantly inhibited digging, nesting, foraging, and attacking behaviors, with performance comparable to the synthetic repellent N, N-Diethyl-m-toluamide (DEET) in multiple laboratory behavioral assays. Soil from P. frutescens -cultivated areas also showed significant repellency, but while the effect on digging behavior diminished before 100 cm, the effect on settlement remained significant at 100 cm. Using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS), we identified eight volatile compounds commonly present in P. frutescens plants, essential oil, and rhizosphere soil: cuparene, limonene, β-caryophyllene, linalool, α-cedrene, perillaldehyde, δ-cadinene, and sabinene. Among these, cuparene, limonene, linalool, perillaldehyde, and δ-cadinene exhibited significant repellent activity at concentrations as low as approximately 0.1 mg/g, with effects positively correlated with concentration. The concentrations used in bioassays were either below or comparable to those naturally released by individual P. frutescens plants under field conditions. Collectively, these findings demonstrate that P. frutescens repels S. invicta through the release of volatile organic compounds (VOCs) into both air and soil, creating a repellent zone that discourages ant colonization. This study provides initial evidence supporting the potential for the strategic use of P. frutescens cultivation in RIFA-infested areas and supports the development of plant-based, environmentally friendly repellent products derived from this species. The findings further highlight P. frutescens as a dual-purpose industrial crop that integrates pest suppression with existing commercial uses.