Repellency of an Over-the-Counter Essential Oil Product in China against Workers of Red Imported Fire Ants

Repellency of an over-the-counter essential oil product from China, and its major components against workers of red imported fire ants, Solenopsis invicta Buren, was evaluated using an ant digging bioassay. Three concentrations (1.0, 10.0, and 100.0 mg/kg in sand) of the product were tested. At 100.0 mg/kg, the digging suppress index (DSI) was 1.0 +/- 0.00 (mean +/- SE) for all six test colonies, indicating this product produced a complete digging suppression; at 10 mg/kg, DSI was 0.22 +/- 0.089 to 0.75 +/- 0.12 and significant repellency occurred against five of six colonies; and at 1.0 mg/kg, DSI was 0.21 +/- 0.091 to 0.38 +/- 0.14 and significant repellency occurred against four of six colonies. The chemical components of this product were analyzed using gas chromatography-mass spectrometry (GC-MS). Camphor, eucalyptol, eugenol, menthol, methyl salicylate, and phenylethanol were identified. A digging bioassay was also conducted on each of those identified compounds at concentrations of 1.0, 10.0, and 100.0 mg/kg. Based on pooled data from three colonies, each component significantly suppressed the digging behavior at 100 mg/kg. Eugenol, menthol, and methyl salicylate significantly suppressed the digging at 10 mg/kg. At 1.0 and 10.0 mg/kg, DSI for eucalyptol was -0.039 +/- 0.032 and -0.050 +/- 0.021, respectively. The negative DSI indicated a digging facilitation. However, only at 10.0 mg/kg, was such facilitation statistically significant.