Hot Water Injection Eradicates Fire Ants in SE Qld

A simple, low-cost, non-chemical treatment has proven to be effective in killing the dangerous fire ant pest at three sites in Australia, according to the results of a Southern Cross University pilot study.

Professor of Entomology Nigel Andrew validated the hot water injection method for removing Red Imported Fire Ants (RIFA) nests in SE Qld. The method is actively used in the USA to complement targeted chemical treatment methods.

Professor Andrew carried out a short-term pilot study in the Logan and Ipswich regions of SE Queensland to identify if the hot water injection method, known as FASO (Fire Ant Soup Operation), is as viable in Australia as it is in the United States in killing all the RIFA nest occupants: queen, winged males, eggs, larvae, pupae and workers.

The method's success in the USA has been peer reviewed and published . There, the method was shown to have a 90% to 100% success rate after four treatments.

"Direct hot water nest injection is a safe and chemical-free method that works by removing fire ant nests from our local environments. Areas treated can be safely used five minutes after treatment," said Professor Andrew.

"Sporting fields can remain open; organic farmers can safely export their produce; landholders wanting a non-chemical option to treat fire ants on their property can all be treated effectively using this option."

Professor Andrew explained what happens to a FASO-treated nest.

"Not only is the RIFA colony killed, but the nest itself is decimated, turning to mud and back into soil," said Professor Andrew.

"Soil invertebrates such as worms and insect larvae were seen active in one dead ant nest three weeks after treatment. Spiders and native ant species return six weeks after fire ants were killed. This indicates that local fauna can recolonise quickly if they are locally present when using this method."

Professor Andrew is preparing for the next phase of the trial.

"Now that we have achieved success in this small field trial, we want to build a few more machines for use locally to expand the range of FASO-treated areas," said Professor Andrew.

"We really want to understand the methods success over the longer term, engaging with local councils, businesses and landholders that are found in sensitive environments."

Professor Andrew is actively working with the developer of the FASO method, Dr Joshua King from the University of Central Florida (ranked Top 5 in innovation among US Public Universities). Dr King won the 2023 Theodore Roosevelt Genius Prize award for developing this method. The Theodore Roosevelt Genius Prize (US$100,000) recognises innovators who are reaching beyond the traditional conservation community to foster technology-driven solutions that can solve conservation challenges.

Additionally, Professor Andrew contracted the services of SE Qld farmer Trevor Hold to assess the feasibility of this method. Mr Hold is currently the only person who has developed the machine in Australia. Until now, no one in Australia has tested this method using this technology.

The direct hot water nest injection method: Fire Ant Soup Operation (FASO)

The FASO method produces hot water which is at 90 °C at the tip of the probe. Hot water is first doused over the top of the nest at around 5-litres/minute (Figure 1). Once the openings are visible, the probe is then inserted into the mound at multiple points (Figure 2). Once the hot water starts to bubble up out of the nest at multiple points (Figure 3), there is a high confidence that the nest has been fully immersed with hot water. Smaller nests may be flooded in five minutes or less. Larger nests can take around 15 minutes to fully flood with hot water.

The effectiveness of the FASO method can be seen immediately. The queens, winged males, the eggs, larvae, pupae and workers are observed dead in the hot water that comes back up from inside the nest.

"This method is not simply just pouring hot water from a kettle onto the top of the nest – the hot water injection is hitting all the ants at temperatures in the nest well above their known limits," said Professor Andrew.

"It kills all nest occupants immediately. And if the first round of FASO is not 100% effective, FASO can be simply reapplied safely a few weeks later. The success of the method can be easily seen as the nest is no longer active, and no new openings within 50cm of the original nest are visible after the FASO procedure."

Pilot data

Two treatments of FASO were carried out at two sites, while one site received a single treatment.

These nest deaths post-FASO treatment indicate that the pilot study has been successful and larger trials in using the method in SE Queensland are warranted.

Next steps

Professor Andrew will apply for grant funding to build FASO machines for use at more locations and assess the longer-term success of FASO. The results from a larger-scale project use will be submitted to a research journal for peer review and open access publication.