Eradicating Little Fire Ants (Wasmannia Auropunctata) from the Island of Kaua`I, Hawai`I: Process, Challenges, and Results to Date

First detected on the Island of Kauai in 1999, the little fire ant (Wasmannia auropunctata) has persisted despite early attempts at eradication by state agencies. A multi-agency collaboration was formed in 2011 to develop and implement a two-phase eradication plan. The infestation was delimited to 4.02 ha of rural residences and steep coastline habitat. Treatments regimens were divided between easily accessible infested areas (Phase I) and steep areas requiring rope safety systems (Phase II). The eradication plan included ground and arboreal treatment technologies and long-term post-treatment monitoring. Treatments consisted of broadcasting baits containing s-methoprene (0.25% a.i.), indocaxarb (0.18% a.i), or hydramethylnon (0.73% a.i.) eight times over the course of 12 months. Treatments effectively reduced the population to below detectable levels throughout much of the treatment area, however isolated remnant colonies were detected as recently as September 2019. Remnant colonies were associated with specific site features known to be difficult to treat, such as tall palm trees and large mulch piles. On one occasion, in 2017, two little fire ant detections were confirmed outside of the original treatment area, where no little fire ants had been detected before; highlighting the ability for little fire ants to remain undetected for many years. Current results stress the importance of long-term commitment to post-treatment monitoring and expanded surveys. We recommend development and incorporation of novel detection methods which could increase accuracy and improve efficiency of monitoring and detection surveys.

Effects of the Invasive Little Fire Ant (Wasmannia auropunctata) on Ant Community Composition on UF Campus

Invasive species are a serious threat to Florida’s native ecosystems and can have significant economic impacts. The invasive little fire ant (Wasmannia auropunctata) was first observed on the University of Florida’s campus in the Field and Fork Gardens in Summer 2018 and a targeted eradication of this population began in Fall 2018. This project aimed to compare ant community composition in invaded and uninvaded areas to better understand how ant invasions affect native ant communities. For comparison with Field and Fork Gardens invaded sites, four additional sites on UF’s campus were surveyed for ants through leaf litter sampling. Samples were sorted and all ants identified to the genus level; samples from invaded sites were identified to species. In samples from invaded sites, the community had lower species richness and a lower relative abundance of ant species compared to uninvaded communities. Determining how the invasion of the little fire ant affects ant communities is important as invasive ants do not fill the same ecosystem roles as native ants, such as seed dispersal and mutualist interactions. Data on community composition in uninvaded areas could be useful in efforts to restore a site after eradication has been achieved.

Using Behavioral Experimentation to Understand the Social Structure of the Little Fire Ant (Wasmannia auropunctata) in Florida

Wasmannia auropunctata (LFA) is a small, yellow ant that is native to the Central and South America that has become a globally invasive species by acting as an agricultural pest in addition to being ecologically destructive in non-native regions. One trait thought to contribute to successful invasion of ants is unicoloniality, which is characterized by lack of aggression among workers and queens from different colonies. This results in colonies becoming effectively borderless, expanding as a single, massive colony across large geographic distance. These ants are known to be unicolonial in some parts of their range, but no studies to date have assessed unicoloniality in Florida populations. To determine whether LFA populations across Florida were members of a unicolonial lineage, we carried out integration trials using 27 colonies from 6 sites in 3 Florida counties. Approximately 20 workers from different colonies were placed together in an arena; after 24 hours they were evaluated to determine whether or not they integrated. Out of a total of 42 trials, 17 (40%) resulted in full integration and 25 (60%) did not. Colonies that were collected within 9 km of each other integrated, and ants from colonies beyond that distance did not integrate. These results suggest that the little fire is not unicolonial in Florida on a large scale, but perhaps on a smaller scale. Future studies should attempt to use colonies from more counties and incorporate genetic data to determine relatedness among these ants.

Ecological impacts of the little fire ant (Wasmannia auropunctata) in Tahiti

The little fire ant (Wasmannia auropunctata) is one of the worst invasive exotic species of the world. Its pantropical expansion is explosive; the ant has been present in Tahiti for more than 20 years. This study is the first to be carried out in Tahiti to assess its ecological impacts. The ecological richness of three invaded environments located in or close to the Key Biodiversity Areas (Maruapo, Papehue, Hopuetamai and Orofero Valleys) was compared with that of adjoining uninvaded sites, in a xerophytic site of ferns and a rainforest in the bottom of a valley for invertebrates and finally a canyon and its cliffs for avifauna. At the last site, one bank is infested and the other bank is free of W. auropunctata. Invertebrates and birds were examined respectively by pitfall traps and observation points. The effects of W. auropunctata were significantly negative at each study site, and species diversity in infested sites was one-third of that in uninfested sites. For arthropods, the phytophages, omnivores, detritivores, predators and other ants were the most affected. Significantly fewer birds also frequented the infested shoreline, particularly endemic birds such as the Tahiti monarch (81% non-infested shoreline observation) and the Society fruit-dove in comparison with the adjacent non-infested shoreline. Moreover, Tahiti monarchs (which are territorial) were established in three territories located at the bottom of the infested zone or close to it in 2016. These birds have now deserted the areas colonised by W. auropunctata. Our results suggest that W. auropunctata is a serious threat to Tahitian terrestrial biodiversity, and related ecosystem services.