Response of Wasmannia auropunctata, (Hymenoptera: Formicidae) to water-soaked imported fire ant baits

Authors: Oi, David; LUCKY, ANDREA - University Of Florida; LIEBOWITZ, DINA - University Of Florida

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2022
Publication Date: 6/10/2022
Citation: Oi, D.H., Lucky, A., Liebowitz, D.M. 2022. Response of Wasmannia auropunctata, (Hymenoptera: Formicidae) to water-soaked imported fire ant baits. Florida Entomologist. 105(2):108-114. https://doi.org/10.1653/024.105.0202.
DOI: https://doi.org/10.1653/024.105.0202

Interpretive Summary: The little fire ant is a stinging invasive ant that can establish extremely large populations in tropical and subtropical regions. In the U.S., it is well established in Hawaii, the US territory of Guam, and south and central Florida. Overwintering populations were discovered in 2018 - 2019 farther north in Gainesville, Florida. There is a need to determine effective management options suitable for the recently discovered and potentially other northern infestations. Ant baits effectively control ants when they feed the bait to other ants within their colony. Moisture is thought to compromise bait effectiveness by making them unpalatable to the ants. Due to the humid and rainy summer weather in north Florida, ARS and University of Florida scientists determined that commercial ant baits soaked in water remained palatable to little fire ants and wet baits that contained nonrepellent active ingredients could significantly suppress and even eliminate colonies of these invasive ants. However, these results should be validated under field conditions, where heavy rains may reduce the accessibility of baits to foraging ants.

Technical Abstract: The little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera: Formicidae) is a stinging invasive ant that can establish extremely large, dominating populations in tropical and subtropical regions. In Florida, it is well established in south and central Florida with a northern limit of Marion County. However, in 2018 – 19 overwintering populations were discovered farther north in Gainesville, Florida. There is a need to develop effective management options suitable for the site uses of these recently discovered infestations. Due to the humid and rainy summer weather in this region, commercial ant baits exposed to moisture were examined for their effectiveness against W. auropunctata. Most commercial imported fire ant baits are formulated on a corn grit carrier, which when exposed to moisture is thought to compromise bait effectiveness. The objective of this study was to determine the acceptance and the efficacy of water-soaked ant baits, some of which had purported moisture tolerance, on W. auropunctata. Bait acceptance tests conducted in the field with dry baits determined that baits containing the active ingredients spinosad and pyriproxyfen were poorly accepted, while W. auropunctata accepted both dry and wet baits containing hydramethylnon, metaflumizone, indoxacarb, and abamectin. Laboratory colonies given access to either dry or wet baits exhibited significant declines in workers, brood, and queens with several colonies being eliminated. The results of this study indicated that water-soaked imported fire ant baits could control W. auropunctata, and moisture exposure did not cause baits to become unpalatable. However, these results should be validated under field conditions, where precipitation may reduce the accessibility of baits to foraging ants.