Effect of Irrigation on the Control of Red Imported Fire Ants (Hymenoptera: Formicidae) by Water-Resistant and Standard Fire Ant Baits

The red imported fire ant, Solenopsis invicta (Buren), is an invasive pest of agricultural, urban, and natural areas. It is also considered a public health pest due to its painful stings. While it can be efficiently controlled by commercially available fire ant baits formulated with a corn-grit carrier, rain or irrigation is thought to degrade the carrier, compromising bait effectiveness. This study assessed the effect of irrigation on the efficacy of water-resistant and standard fire ant bait formulations, by comparing worker number, brood volume, and queen survivorship after access to water-soaked baits and to irrigated, bait-treated sod. In initial testing, wetted water-resistant and standard baits reduced fire ant colonies less than dry baits, both when baits were given to colonies directly and when colonies were given access to baits broadcasted (i.e., scattered) atop sod. Comparisons of the efficacy of piled versus broadcast applications of water-resistant and standard baits revealed reductions of >88% in adults 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. In a field study, irrigated water-resistant and standard baits caused similar and significantly higher reductions in fire ant foraging activity relative to an untreated control. These results indicated that both the water-resistant and standard fire ant bait provided significant fire ant reductions even after irrigation.