Managing imported fire ants with the essential oil of Alaskan yellow cedar (Cupressus nootkatensis)

The essential oil of Alaskan yellow cedar contains several sesquiterpenes with demonstrated insecticidal and repellent effects. The major components include nootkatone (2%), carvacrol (6%), valencene (15%) and nootkatene (57%). Laboratory and field bioassays were conducted to assess the oil's repellent and insecticidal effects.  In contact assays, 80% mortality was observed in the 1% solution, with 100% in the 10% solution.  In fumigation assays, a rate of 100 ul/L resulted in 100% mortality. In a digging assay, 0.1 ul of oil applied to 35 g of sand in 7 dram vials inhibited ant removal of sand. The repellency observed in the 100ul application in the digging assay lasted for 6 months, with 50% less sand removed in the 6 month old treatment as the controls. A drench test of fire ant mounds using 2 ml/gallon of oil compared with the standard Onyx Pro (bifenthrin) treatment and a water control resulted in 80% mortality of fire ant mounds at 10 weeks versus 93% for OnyxPro and 33% for the control mounds. A band test of nootka oil and Onyx at a nursery field site showed that nootka oil achieved 93-94% mound suppression from 4-17 weeks post treatment, while Onyx achieved 100% control from weeks 2-17. We conclude that the active compounds in nootka oil may be used to successfully manage imported fire ants.