Effect of irrigation on the control of fire ants by water-resistant and standard fire ant bait

The red imported fire ant, Solenopsis invicta, is one of the world’s most damaging invasive ants. In addition to being an agricultural, urban, and nature reserve pest, it is also considered a public health pest due to its painful stings. Many commercially available fire ant baits are formulated on a corn grit carrier, which is thought to degrade when exposed to rain or irrigation, and compromise bait effectiveness. To emulate landscape irrigation, the efficacy of water-resistant and standard fire ant bait formulations against fire ant colonies was compared on sprinkler irrigated pieces of sod. In initial testing, fire ant reductions were less on irrigated baits than on dry baits when the bait was broadcasted (i.e., scattered) atop the sod. Nevertheless, reductions in workers were significantly greater than the control. Comparisons of the efficacy of piled versus broadcast applications of standard and water-resistant baits revealed reductions of >88% in adult and brood and no surviving queens for all bait treatments. This result was unexpected because piled baits were hypothesized to be better protected from irrigation than broadcast bait applications. These results indicated standard fire ant bait exposed to irrigation does not completely negate fire ant control.