How to know if we’re winning the war on Australia’s fire ant invasion, and what to do if we aren’t

Fire ants like these can give a nasty bite.
Shutterstock/SweetCrisis

Daniel Spring, University of Melbourne and Jonathan Keith, Monash University

More than A$400 million of government funding is being invested in the latest round of the fire ant program in the hope of eradicating the invasive pests by 2027.

But recent reports on the ABC suggest the invasion is spreading beyond containment lines in south-east Queensland, and there are delays in responding to public reports of new ant infestations.

The claims are denied by Graeme Dudgeon, the new general manager of Queensland Government’s National Red Imported Fire Ant Eradication Program.

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Fire ants are native to South America but nests were first discovered in Brisbane in 2001. It’s thought they arrived via shipping at the Port of Brisbane.

They’re regarded as one of the world’s worst invasive species and have a painful bite which is why the Queensland Government has been trying to wipe them out here.

Is eradication possible?

An independent review in 2016 found the fire ants were confined to a region of south east Queensland and said there was an opportunity to eradicate the pests.

But the latest debate raises the question of whether eradication is the best plan, or would further containing the spread of the fire ants be a more practicable solution?

To achieve its aim of eradicating the fire ant problem, the program needs to progressively shrink the invasion.

If the invasion is shrinking too slowly (or is expanding), eradication won’t be achieved by 2027. Without ongoing monitoring of the invasion’s size, the program might be failing without the general public knowing.

But knowing the fire ant invasion’s size isn’t easy because there isn’t enough funding to survey all locations that might have them.

Estimates of the invasion

Using records of past fire ant detections, we have demonstrated how to estimate the invasion’s size when only part of the managed area is surveyed.

Our inference of the boundary of the fire ant invasion in April 2015. The different coloured polygons correspond to different levels of credibility that the boundary contains the invasion, with the outermost boundary corresponding to the highest credibility. Small crosses represent sites where nests have been detected, with the most recent detections in red and the oldest in brown.
Nature/Authors provided, CC BY

If this approach to estimating the invasion boundary is applied each year during the current program, we could estimate whether the invasion is shrinking fast enough to be gone by 2027.

The importance of this issue demands a rigorous scientific analysis using transparent data and methods. Without this, anecdotal evidence that the current invasion is spreading is all we have to indicate whether eradication efforts are failing.

The size of the fire ant invasion should not only be measured in terms of the total area within its estimated boundary but also the density of nests within this area.

Eradication won’t be achieved if both the invasion boundary and the density within it are increasing. This straightforward test to determine whether the program is failing has not yet been applied.

But such a test could be done if updated records of the fire ant invasion are regularly made available to allow for periodic estimation of updated maps of the invasion.

Never give up

Even if eradication by 2027 is unlikely, this does not mean we should give up, provided future control efforts can contain the invasion at an affordable cost.

If the current program fails to eradicate the fire ants, it may still set the stage for effective long-term containment of the invasion.

A poor outcome will result if current management efforts are spread thinly over the infested area, reducing the density of nests but not eradicating them from any suburbs.

A better outcome would involve shrinking the infested area, that is, eradicating the ants from many or most suburbs, so that subsequent containment efforts can focus resources on a smaller area.

Is it still early enough in Australia to shrink the fire ant invasion to a manageably small area and thereby protect most homes and most of the environment for a long time? The required information to answer this question is not yet available.

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But if Queensland’s eradication program has substantially slowed the spread so far, this provides confidence that continuing the program could effectively suppress the invasion. If so, we need to estimate what it will cost to keep out fire ants from most homes and most of the environment for a long time.

It’s often claimed that removing the last 1% of invaders costs as much as removing the previous 99%. If the current program removes all ants from most areas by 2027, this may provide large benefits without the extra cost of finding the last few ants in all infested areas.

Even if we do eradicate fire ants this time, it’s almost certain they will be back because they can readily hitchhike rides on ships.

So if governments can keep fire ant numbers down through ongoing containment, a lot of people and a lot of native species will benefit.

Daniel Spring, Research Fellow, School of Biosciences, University of Melbourne and Jonathan Keith, Associate Professor, School of Mathematical Sciences, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Cannibalism helps fire ants invade new territory

Fire ant stings can be deadly to people who have an allergic reaction to their venom.
Forest and Kim Starr/Flickr, CC BY-SA

Pauline Lenancker, James Cook University and Lori Lach, James Cook University

Tropical fire ants (Solenopsis geminata), originally from central and South America, are a highly aggressive, invasive ecological pest. Our new research has shed light on how they successfully establish new colonies.

An allergic reaction to painful tropical fire ant bites.
Pauline Lenancker, Author provided

While we don’t know exactly how widespread tropical fire ants are in Australia, they are well established around Darwin and Katherine, as well as on Christmas Island and Ashmore Reef. Disturbing one of their nests will result in many workers inflicting painful stings on the intruder, and can trigger an allergic reaction in some people.

When invasive ants move to a new region, the pioneers may be one or a few colonies. Because these pioneers are isolated, they often inbreed, which causes genetic problems in their offspring. But our new research, published in Scientific Reports, reveals how tropical fire ants use cannibalism to survive and spread, despite their low genetic diversity.

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Sons and daughters

Founding new colonies is how fire ants spread. Queens fly off to start their own colonies just after they have mated. It is a perilous journey – they need to avoid predators and find a good spot to start laying eggs. If queens do not quickly rear daughters that can forage, called workers, they will starve to death.

Queens can lay two different types of eggs: fertilised eggs, which will develop into workers, and unfertilised eggs, which will develop into males. Therefore, female workers have two copies of each gene (diploid), while males have a single copy of each gene (haploid). However, when an ant queen and her mate are closely related, a flaw in the sex determination system of ants causes half of the fertilised eggs to develop into diploid males instead of workers.

The role of males is only to mate with queens – they do not forage, and they die after they have mated. Queens founding a colony have no interest in producing males, because males will not feed them. What’s more, diploid males are often sterile, and their larvae are larger than worker larvae. Therefore, queens can waste precious resources feeding fat useless sons instead of workers.

We wanted to find out how common diploid males are in field colonies, and how queens could successfully start colonies despite them. Understanding how tropical fire ants spread, we hope, can help us stop them expanding their range.

Abandoned and eaten

Our field sampling of tropical fire ant colonies around Darwin revealed eight out of ten colonies produced diploid males.

We collected 1,187 queens that had just mated, and assigned them to start colonies on their own or with other queens.

We observed that in 34% of colonies producing diploid males, diploid male larvae were placed in the colony trash pile by the queens instead of being kept with the worker larvae. It is usual for ants to keep dead individuals away from the rest of the colony, but when we looked at some of these abandoned larvae under a microscope, we realised they were still alive.

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Queens not only abandoned their sterile sons, they ate them. Three-quarters of the 109 sterile male larvae disappeared from the colonies within 12 days of when we first observed them. Because the queens were the only adult ants present in the colony, this means the queens were eating their diploid males or feeding them to their worker larvae.

This cannibalistic behaviour allowed the queens to redirect nutrients towards themselves or productive members of their colony. Diploid male larvae require more food than worker larvae to develop, so we expected queens from diploid male producing colonies to lose more weight than queens from colonies that only produced workers, but we found that was not the case. Queens with diploid males lost less weight or as much weight as queens from regular colonies, probably because they ate their sterile sons.

We also found queens who worked together in groups to start a colony reared more workers. Therefore, queens in groups would likely have a better chance of survival even if they produced sterile males. But in 6% of colonies, queens did not tolerate having housemates and dismembered other queens.

A queen dismembered by a tetchy rival.
Pauline Lenancker, Author provided

For tropical fire ants, cannibalising sterile sons and cooperative brood rearing among queens are two behavioural mechanisms for avoiding inbreeding costs. A third possible mechanism for the queens is to “sleep around”.

Promiscuity would increase the chance of mating with a genetically different male, and reduce the likelihood of producing diploid sons.

Queens only mate right before starting their colony and store the sperm in an organ called the spermatheca. We genetically analysed sperm from the spermatheca of 40 queens, but found no evidence queens had mated with more than one male.

Tropical fire ants are currently established on Ashmore Reef, a protected Australian Marine Park which is an important breeding site for seabirds and turtles. The invasive ant threatens this sanctuary by attacking seabird and turtle hatchlings. Accidental spreading of tropical fire ants to suitable habitats in the Northern Territory, Queensland and Western Australia would threaten invaluable ecosystems as well as our health and lifestyles.

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The current eradication program for the closely related red imported fire ant (Solenopsis invicta) in Queensland has been granted A$411 million over ten years, and failure to eradicate red imported fire ants could cost Australia A$1.65 billion per year in damaged crops, livestock harmed and people treated. The more we learn about invasive ant biology, the closer we are to new methods of preventing their spread.

Pauline Lenancker, PhD student in biology and ecology, James Cook University and Lori Lach, Associate Professor, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Eradicating fire ants is still possible, but we have to choose now

Daniel Spring, University of Melbourne; Jonathan Keith, Monash University, and Tom Kompas, University of Melbourne

Australia needs to spend millions of dollars more to eradicate one of the nation’s worst invasive species, the fire ant, according to recent reports.

Fire ants, first detected in Brisbane in 2001, pose a major health and agricultural risk. A recent independent review of the eradication program recommended that A$380 million be spent over 10 years to eradicate the ants, on top of the A$330 million already spent since 2001.

Improvements in knowledge and control methods mean that eradicating the Australian invasion is challenging, but still potentially feasible. We now face a stark choice.

Lessons from previous attempts

The fire ant eradication program began in September 2001 after the species was detected at two locations in Brisbane. By that time, it may have been present for at least five years or perhaps even longer, and large areas were already infested. Fire ants had never been eradicated from areas this large.

However, improved eradication methods mean we have increased the chances of eradicating larger invasions.

Most of the original funds were spent on pesticides and monitoring areas with likely infestations. Monitoring information was used to estimate how far the invasion had spread (“delimitation”) and management efforts were focused on the delimited area.

The early years of the program showed that large infestations, such as those at the Port of Brisbane and Yarwun, can be eradicated when the geographic range of the infestations is known.

However, when this is not the case, undetected nests beyond the known infested area can spread unchecked. In a published reconstruction of the invasion we estimated that undetected nests existed a relatively short distance beyond the delimited area.

Had those nests been detected by monitoring a larger area over the first few years of the program, the ants may already have been eradicated. However, the initial focus on intensively treating known infestations rather than expanding the monitored area reflected the best available scientific advice at the time.

It also reflected an urgent need to protect people from the potentially serious health consequences of coming into contact with fire ants in areas known to be infested.

Pustules caused by fire ant stings.
Daniel Spring, Author provided

Is eradication still possible?

Although the invasion now occupies a larger area than it did when the program began, fire ant numbers have effectively been suppressed and some individual infestations have been eradicated. These facts, and the availability of a cheaper monitoring method involving remote sensing with airborne cameras, have kept alive eradication hopes.

A recent meeting of agricultural ministers agreed with the finding of the independent review that eradication remains technically feasible.

The review’s recommendation that eradication program funding be increased is a logical response to the invasion’s expansion. The expansion not only increased the area that requires management, thus increasing costs, but also showed that the areas previously searched and treated each year were too small to achieve eradication, implying there was insufficient annual funding.

Geographic expansion of the invasion cannot continue much longer without the invasion becoming too large to eradicate. The review panel’s finding that increased funding should be made available soon is therefore timely.

A lack of monitoring during the early years of the program led to the erroneous conclusion in 2004 that eradication was imminent, when in fact the invasion was expanding in area. To avoid this mistake being repeated, substantial monitoring will be required beyond known infestations and monitoring data will need to be assessed with reliable statistical methods.

In a recent report we wrote to help the eradication program, we showed that the invasion boundary can be estimated with a high degree of confidence if adequate monitoring data are available.

Pesticide treatment and monitoring will underpin eradication efforts. We need highly sensitive monitoring methods, including sniffer dogs and trained spotters, to confirm absence of fire ants in and near treated locations.

A large enough area should be monitored to ensure all fire ant colonies are found and removed. We need continued support for community members to report fire ants, particularly in urban areas. Remote sensing will be needed in less developed areas where contact between people and fire ants is less likely.

A stark choice

The choice is to continue eradication efforts or live with fire ants forever. Living with fire ants will incur large costs for agricultural producers and households.

The most recent cost-benefit analysis of the program estimated that if these costs were added up over each of the next 70 years they would exceed A$25 billion in today’s dollars.

Over half these estimated costs arise from damage to agricultural activities, with household losses being of a similar magnitude.

Large numbers of people are likely to come into contact with fire ants if the species is left unchecked. Environmental damages could also be substantial. These losses far exceed estimated eradication costs.

The review panel’s report makes it clear that we face an urgent choice between increased eradication funding or living with fire ants. There is not much time left to make this choice.

Daniel Spring, Research Fellow, School of Biosciences, University of Melbourne; Jonathan Keith, Associate Professor, School of Mathematical Sciences, Monash University, and Tom Kompas, , University of Melbourne

This article was originally published on The Conversation. Read the original article.

Australia: NSW – Fire Ants in Sydney

The link below is to an article warning of a Fire Ant invasion of Sydney – this is a very important problem and warning for Sydney.

For more visit:
http://www.mygc.com.au/news/fire-ant-invasion-poses-higher-risk-than-sharks/

Australia: Queensland – Gold Coast Fire Ants