Objective The red imported fire ant, Solenopsis invicta Buren, is one of the world's most destructive invasive species, posing significant threats to public safety, agricultural and forestry production, and the ecological environment. The Tibetan medicine Delphinium brunonianum Royle possesses a strong aromatic odor and a wide range of biological activities. However, its essential oil composition and repellent activity against S. invicta are still unclear. This study focuses on analyzing the chemical composition of the essential oil from D. brunonianum and screening it for active constituents to identify natural repellents effective against S. invicta.

Method The essential oil of D. brunonianum was extracted via steam distillation, and its chemical composition was analyzed using GC-MS. Bioactive components that elicit electrophysiological responses in the antennae of S. invicta were screened by GC-EAD. Furthermore, the repellent activity of the essential oil and its key compounds against S. invicta was evaluated through sand-digging test and Y-plate test.

Result A total of 32 peaks were identified in the essential oil of D. brunonianum, with 18 compounds being characterized, accounting for 91.25% of the total composition. The main components include palmitic acid (30.49%), phytol (17.33%), manoyl oxide (11.25%), linolenic acid (6.68%), methyl linolenate (5.93%), and phytone (4.86%), however, the relative contents of other components were each below 2.5%. Besides, phytone, manoyl oxide, methyl linolenate, and phytol in the essential oil elicited significant EAD responses in S. invicta, and the values were positively correlated with concentration. The EAD response value induced by phytone was 0.13 mV, which was significantly higher than phytol and methyl linolenate (0.07 mV and 0.04 mV, respectively) at the concentration of 5 μL/mL. In addition, the essential oil of D. brunonianum, as well as phytone and phytol significantly reduced the sand-digging activity and Y-plate selection rate of S. invicta, and the highest repellency rates reached 91.18%, 90.46%, and 88.52%, respectively, with the concentration range from 0.5 to 5 μL/mL. However, in the sand-digging test (at 0.5 μL/mL) and the Y-plate test (at 5 μL/mL), methyl linolenate exhibited a weak attractant effect on S. invicta.

Conclusion This study has identified the main components of D. brunonianum essential oil, and both the essential oil and its repellent active compounds, phytol and phytone, were demonstrated potential for development as natural repellents against S. invicta.