A provocative new international study published in Austral Ecology warns the massive 'broadcast baiting' campaign currently used to combat Red Imported Fire Ants (RIFA) in south-east Queensland may be doing more harm than good.
Quick facts
A new international study shows large-scale use of non-specific pesticides, known as insect growth regulators (IGRs), inadvertently enables fire ants to expand their territory.
Applications of IGRs on areas larger than 10,000-hectares have never been successful in eradicating fire ants; the current area that fire ants occupy in SE-Qld is now over 1-million hectares.
Invasive species, such as fire ants, rebounded quicker than native invertebrate species after being exposed to pesticides such as IGRs at large scales, enabling them to recolonise areas baited and to colonise areas where native competitors and predators have been removed via baiting.
Researchers recommend moving from a one-size-fits-all eradication approach to precision, fire ant-specific strategies.
A provocative new international study published in Austral Ecology warns the massive "broadcast baiting" campaign currently used to combat Red Imported Fire Ants (RIFA) in south-east Queensland may be doing more harm than good.
Researchers from Southern Cross University (Australia) and the University of Central Florida (USA) suggest the use of non-specific pesticides, known as insect growth regulators (IGRs), is inadvertently paving the way for the invasive ants to expand their territory.
The study's authors Southern Cross University's Professor Nigel Andrew and Professor Joshua King University of Central Florida highlight a critical "ecological vacuum" effect. By spreading insect pesticides such as IRGs over areas of south-east Queensland, current programs are killing off the native invertebrate competitors and predators that serve as the first line of defence against fire ant queens.
"We are essentially clearing the neighbourhood for the fire ant invader when we mass-release IRGs into the environment over large areas," says Professor Andrew.
"By doing so we inadvertently remove native invertebrate competitors and predators in areas next to RIFA infestations. As a result, RIFA queens have a much higher success rate in establishing new colonies.
"Because RIFA are faster at recolonising recently treated areas than our native invertebrate species, the current strategy may be facilitating a faster spread rather than achieving eradication."
An innovative pest that remains one-step ahead
Professor Andrew explained that RIFA behave covertly when establishing new subterranean nests.
"RIFA mating flights most frequently occur after rain events, up to 10 or more times, with more than 2,000 queens released a year from a mature nest. A mated queen usually does not fly further than 100-metres from her mother's nest," said Professor Andrew.
"When a RIFA queen lands in a new area, she and her first batch of minute workers stay locked away in a plugged nest for three to four weeks and will not start to take up baits for more than a month.
"Any IGRs released during that time will not be taken up by these new RIFA nestmakers. The baits will lay around and be taken up by other insects and invertebrates. If those other insects are susceptible to disruption of their life cycles by IGRs, their offspring will die."
The paper points out that while broadcast baiting works well for small RIFA infestations (under 10,000 ha), the current south-east Queensland infestation is 100 times larger than any area ever successfully eradicated worldwide.
The need for a biological pivot
The researchers argue that the "one size fits all" approach must be abandoned in favour of precision, species-specific strategies. To achieve true eradication, further research is urgently needed in the following areas:
- Specific RIFA biology: Identifying unique physiological and behavioural traits – such as specific odorant receptors – to create baits that only fire ants will take.
- Landscape integration: Using natural landscape features and invertebrate competitors to create "resistance zones" that naturally suppress RIFA movement.
- Precision nest targeting: Moving toward direct nest injection (chemicals; or hot water (FASO method)) and targeted baiting (eg subterranean bait stations) that leaves the surrounding ecosystems intact.
"We need a strategic shift," Professor Andrew concludes.
"If we don't move toward adaptive, ecologically sensitive management that respects the role of biodiversity in urban backyards, industrial parks and rural properties, we risk spending billions of dollars only to help the fire ants win."
How the study was conducted
The findings were generated from a knowledge of the literature on ant ecology, pest management and impacts on non-target species, an understanding of RIFA biology, and an understanding of why previous eradication efforts, particularly in the USA, have failed. It also came from acknowledging the lack of information that science and society has about releasing IGRs into the natural, rural, and urban environments at a landscape scale.
"Australia has no reliable information about what impact IGRs will have over time at such a large scale; on which invertebrate species; and how these impacts may change the environment," said Professor Andrew.
Professor Nigel Andrew is the current awardee of the Australian Entomological Society Ian Mackerras Medal (2024) for mid-career excellence in entomology. He has extensive experience in insect ecology, particularly ants, and insect responses to a changing environment.
Professor Joshua King won the 2023 Theodore Roosevelt Genius Prize Competition for the Protecting Endangered Species for his work on RIFA. He has more than 25 years of experience studying RIFA and is the world leader in understanding their ecology and impacts on their environment.
View the evidence from the scientific literature.
