Repellent Effect of Formic Acid Against the Red Imported Fire Ant (Hymenoptera: Formicidae): A Field Study

Previous studies showed that the formic acid secreted by tawny crazy ants not only has fumigation toxicity to the red imported fire ant, Solenopsis invicta Buren (Chen et al. 2013), but also can detoxify fire ant venom (LeBrun et al. 2014). These lead us to a field study to determine if low concentrations of formic acid might be useful in repelling S. invicta. Filter paper discs treated with 1.3% or 5% formic acid (v: v) or distilled water (control) were placed on each of the 46 S. invicta mounds and a disturbance was created. For a minute or less, there were significantly more defending ants on the control discs than that on the paper discs treated with formic acid. After food was added and for the next 40 min, there were significantly more foraging ants on the control discs compared to the treated discs. At 50 min into the test, the number of foraging ants on the control and 1.3% formic acid-treated discs was similar, but both were significantly higher than that on the 5% formic acid-treated discs. In addition, the active foraging (≥10 ants stayed on or around the food) and burying behavior (soil particles were deposited around the food) continued to be inhibited by 5% formic acid. The potential application and ecological significant of this repellent effect is discussed.