After decades away, dengue returns to central Queensland



Australia’s dengue cases are usually limited to far north Queensland.
Shutterstock

Cameron Webb, University of Sydney

The Queensland city of Rockhampton was free of dengue for decades. Now, a case of one of the most serious mosquito-borne diseases has authorities scratching their heads.

Over the past decade, dengue infections have tended to be isolated events in which international travellers have returned home with the disease. But the recent case seems to have been locally acquired, raising concerns that there could be more infected mosquitoes in the central Queensland town, or that other people may have been exposed to the bites of an infected mosquito.

What is dengue fever?

The illness known as dengue fever typically includes symptoms such as rash, fever, headache, joint pain, vomiting, diarrhoea, and abdominal pain. Symptoms can last for around a week or so. Four types of dengue virus cause the illness and they are spread by mosquito bites.

Once infected, people become immune to that specific dengue virus. However, they can still get sick from the other dengue viruses. Being infected by multiple dengue viruses can increase the risk of more severe symptoms, and even death.

Hundreds of millions of people are infected each year. It is estimated that 40% of the world’s population is at risk given the regions where the virus, and the mosquitoes that spread it, are active. This includes parts of Australia.




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The last significant outbreak in Australia occurred in far north Queensland in 2009, when more than 900 people were infected by local mosquitoes.

Only a handful of locally acquired cases have been reported around Cairns and Townsville in the past decade. All these cases have two things in common: the arrival of infected travellers and the presence of the “right” mosquitoes.

The dengue virus isn’t spread from person to person. A mosquito needs to bite an infected person, become infected, and then it may transmit the virus to a second person as they bite. If more people are infected, more mosquitoes can pick up the virus as they bite and, subsequently, the outbreak can spread further.

Why are mosquitoes important?

Australia has hundreds of different types of mosquitoes. Dozens can spread local pathogens, such as Ross River virus, but just one is capable of spreading exotic viruses such as dengue and Zika: Aedes aegypti.

Aedes aegypti breeds in water-holding containers around the home. It is one of the most invasive mosquitoes globally and is easily moved about by people through international travel. While these days the mosquito stows away in planes, historically it was just as readily moved about in water-filled barrels on sailing ships.

Aedes aegypti is the mosquito primarily responsible for the spread of dengue viruses.
By James Gathany – PHIL, CDC, Public Domain

The spread of Aedes aegypti through Australia is the driving force in determining the nation’s future outbreak risk.

The mosquito was once widespread in coastal Australia but since the 1950s, it become limited to central and far north Queensland. We don’t really know why – there are many possible reasons for the retreat, but the important thing now is they don’t return to temperate regions of the country.

Authorities must be vigilant to monitor their spread and, where they’re currently found, building capacity to respond should cases of dengue be identified.




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What happened in Rockhampton?

Last week, for the first time in decades, a locally acquired case of dengue was detected in Rockhampton, in central Queensland. The disease was found in someone who hasn’t travelled outside the region, which suggests they’ve been bitten locally by an infected mosquito.

This has prompted a full outbreak response to protect the community from any additional infected mosquitoes.

While the risk of dengue around central Queensland is considered lower than around Cairns or Townsville, authorities are well prepared to respond, with a variety of techniques including house-to-house mosquito surveillance and mosquito control to minimise the spread.

These approaches have been successful around Cairns and Townsville for many years and have helped avoid substantial outbreaks.

The coordinated response of local authorities, combined with the onset of cooler weather that will slow down mosquitoes, greatly reduces any risk of more cases occurring.

What can we do about dengue in the future?

Outbreaks of dengue remain a risk in areas with Aedes aegypti mosquitoes. There are also other mosquitoes, such as Aedes albopictus (the Asian tiger mosquito), that aren’t currently found on mainland Australia but may further increase risks should they arrive. Authorities need to be prepared to respond to the introductions of these mosquitoes.




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While a changing climate may play a role in increasing the risk, increasing international travel, which represents pathways of introduction of “dengue mosquitoes” into new regions of Australia, may be of greater concern.

There is more that can be done, both locally and internationally. Researchers are working to develop a vaccine that protects against all four strains of dengue virus.

Others are tackling the mosquitoes themselves. Australian scientists have played a crucial role in using the Wolbachia bacteria, which spreads among Aedes aegypti and blocks transmission of dengue, to control the disease.

The objective is to raise the prevalence of the Wolbachia infections among local mosquitoes to a level that greatly reduces the likelihood of local dengue transmission.

Field studies have been successful in far north Queensland and may explain why so few local cases of dengue have been reported in recent years.

While future strategies may rely on emerging technologies and vaccines, simple measures such as minimising water-filled containers around our homes will reduce the number of mosquitoes and their potential to transmit disease.The Conversation

Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney

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

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Sit! Seek! Fly! Scientists train dogs to sniff out endangered insects


Julia Mynott, La Trobe University

Three very good dogs – named Bayar, Judd and Sasha – have sniffed out the endangered Alpine Stonefly, one of the smallest animals a dog has been trained to successfully detect in its natural habitat.

The conservation of threatened species is frequently hampered by the lack of relevant data on their distributions. This is particularly true for insects, where the difficulty of garnering simple information means the threatened status of many species remains unrecognised and unmanaged.




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In alpine areas there is a pressing need for innovative methods to better reveal the distribution and abundance of threatened insects.

Alpine regions rely on cool temperatures, and since climate change will bring warmer weather and lower rainfalls, insects like the Alpine Stonefly, which lives in the alpine freshwater system, will struggle to survive.

And while insects might not be appealing to everyone, they are extremely important for ecosystem function.

Traditional survey detection methods are often labour intensive, and hard-to-find species provide limited information. This is where the labrador, border collie and samoyed came to the rescue.

La Trobe’s Anthrozoology Research Group Dog Lab in Bendigo, Victoria have been training a pool of local community volunteers and their dogs in conservation detection to use with environmental DNA sampling. Using both environmental DNA and detection dogs has the potential to generate a lot of meaningful data on these threatened stoneflies.

For seven weeks in a special program, dogs were trained to memorise the odour of the Alpine Stonefly (Thaumatoperla alpina), a threatened but iconic insect in the high plains.

The dogs have previously been trained to sniff out animal nests or faeces but not an animal itself, so this was a new approach and an Australian first.

Stoneflies are hard to catch

The Alpine Stonefly are brightly coloured aquatic insects and are difficult to find, especially as larvae in water where they live as predators for up to two years in the streams on the Bogong High Plains, Mount Buller-Mount Stirling, Mt Baw Baw and the Yarra Ranges.

They often burrow underneath cobbles, boulders and into the stream bed while the adults only emerge from the water for a few months between January and April to reproduce.

With all this in mind, it’s easy to understand why traditional detection methods can be time consuming and often ineffective.

We predominately focused on the endangered Alpine Stonefly, found across the Bogong High Plains. Their restricted distribution and habitat made them an ideal candidate to trial detection dogs and environmental DNA techniques.




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How dogs and environmental DNA help

We collected water samples from across the Bogong High Plains, Mount Buller and Mount Stirling with trace DNA, such as cells shed from the insect. The ability to quickly take these samples from a broad area to indicate the presence of a species is important to understand distribution. But this approach limits the amount of ecological information that is gathered.

Initial training introduced the dogs to the odour of the Alpine Stonefly in a controlled laboratory setting. Then they graduated from the laboratory to small areas of bushland to search for the insect.

Once the dogs successfully completed their training, it was time to trial the dogs in the alpine environment and survey Alpine Stoneflies in their natural environment.

The trial was conducted at Falls Creek with the dogs’ three volunteer handlers. And the surveys were successful, with all three dogs finding Alpine Stoneflies in their natural habitats.

So could this success be transferred to a similar species?

Absolutely. In preliminary trials, Bayar, Judd and Sasha detected the Stirling Stonefly, a related species of Thaumatoperla that lives in Mount Buller and Mount Stirling, suggesting detection dogs can transfer their conservation training from one species to another.

This is a great find as it means this technique can be used to survey yet another species of Thaumatoperla that lives in Mt Baw Baw and the Yarra Ranges.




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Our research is showing that these new sampling techniques supporting conservation are an important part of keeping biodiversity protected in alpine regions.

Now that we’ve successfully trained three dogs, we’re hoping to secure funding to conduct future and more thorough surveys on the Alpine and Stirling Stonefly, and eventually on the third species of stonefly.

By developing creative techniques to detect these species, we boost our ability to document them and, importantly, to protect them.The Conversation

Julia Mynott, Research Officer, Centre for Freshwater Ecosystems, La Trobe University

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

Bees seeking blood, sweat and tears is more common than you think



File 20190412 76837 1czhl8p.jpg?ixlib=rb 1.1
Known sweat-collecting stingless bees, Tetragonula sp., from the bee family Apidae.
Tobias Smith, Author provided

Manu Saunders, University of New England and Tobias Smith, The University of Queensland

The recent story of four live bees pulled from inside a woman’s eye quickly grabbed people’s attention. News reports claimed the bees were “sweat bees”, the common name for species in the bee family Halictidae.

There are some contradictory and unlikely statements in the many news reports covering this story, so it’s hard to know what actually happened. The images accompanying many reports, which some reporters captioned as the live sweat bees in the Taiwanese woman’s eye, are actually uncredited images from a completely unrelated story – this report by Hans Bänzinger of a stingless bee species (Lisotrigona cacciae) collecting tears from his eye in Thailand.


The Guardian/ Bees (Hymenoptera: Apidae) That Drink Human Tears, in Journal of the Kansas Entomological Society.

All in all, we would consider it extremely unlikely for multiple adult insects to survive inside a human eye for very long. Most halictid bees are too large to get trapped in your eye unnoticed. Female sweat bees also have stingers so you would definitely know straight away!

But whether this story is accurate or not, there are bees who would happily feast on human tears – and blood, sweat and even dead animals. Flower-loving insects like bees and butterflies often seek out other food sources that are at odds with their pretty public image.




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Un-bee-lievable

So why would bees hang around someone’s eye in the first place? It’s a bit of a myth that all bees only collect pollen and nectar for food. There are bee species all over the world that also feed on the bodily fluids of living and dead animals, including animal honeydew, blood, dead meat, dung, sweat, faeces, urine and tears. This is a source of important nutrients they can’t get from flowers, like sodium, or protein and sugar when floral resources are scarce.




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The term “sweat bee” is used colloquially for bees that ingest human sweat as a nutritional resource.

Many people think the term only refers to bees in the Halictidae family. But not all halictid bee species are known to collect sweat, while many species in the Apidae family, particularly stingless bees, are common sweat-collectors in tropical areas around the world. Swarms of sweat-seeking stingless bees can be a nuisance to sweaty humans in tropical places.

And it’s not just sweat; stingless bees have quite diverse tastes and collect many non-floral resources. There are also a few neotropical Trigona species that collect animal tissue as their main protein source, instead of pollen. These species collect floral nectar and make honey, like other stingless bees, but predominantly scavenge on carrion (they are technically know as obligate necrophages).

Vulture bees feed on rotting meat rather than pollen or nectar.
Wikipedia/José Reynaldo da Fonseca, CC BY-SA

Regardless of taxonomy, bees that are attracted to sweat often use other bodily fluids too, like tears. Tear-feeding is such a common behaviour among insects, it has an official name: lachryphagy. Some stingless bees from south Asia, such as the Lisotrigona species mentioned above, are well-known lachryphagous insects, often seen congregating in groups around animal eyes (including humans) to harvest fluids. They don’t harm the animal in the process, although their activity might be a nuisance to some.

In South America, Centris bees are large, solitary apid bees, in the same family as stingless bees and honey bees. These bees are often observed drinking tears from animal eyes; published observations include interactions with caimans and turtles.

Bees aren’t the only insects that regularly drink from animal eyes. Our world-famous hand gesture, the Aussie salute, is designed to deter the common bush flies (Musca species) that hang around our faces on hot days, looking for a quick drink of sweat, saliva or tears. These flies are also commonly seen clustered around livestock eyes on farms.

The feeding habits of butterflies would shock many people who think they are dainty, angelic flower-frequenting creatures. Butterflies are common feeders on dung, carrion, mud and various other secretions, including animal tears. Moths are also well-known nocturnal feeders on animal tears, even while they are sleeping.

Julia butterflies drinking the tears of Arrau turtles in Ecuador.
Wikimedia/amalavida.tv, CC BY-SA

Although most of us wouldn’t like the idea of an insect drinking out of our eyelid, this isn’t the stuff of nightmares. It’s just another fascinating, but little-known, story of how animals interact with each other. From a bee’s perspective, an animal’s eye is just another food source.




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It produces secretions that provide important nutrients, just like a flower produces nectar and pollen. Although entomologists know this behaviour occurs, we still don’t fully understand how common it is, or how reliant pollinating insects are on different animals in their local environment.

But, while tear-collecting behaviour is normal for many insects, the odds of live bees crawling inside your eye to live are extremely low.The Conversation

Manu Saunders, Research fellow, University of New England and Tobias Smith, Ecologist, bee researcher and stingless bee keeper, The University of Queensland

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

Invasive ants: federal budget takes aim but will it be a lethal shot?



File 20190404 131415 1ag8r2w.jpg?ixlib=rb 1.1
Argentine ants are a fact of life in many parts of Australia, but can still potentially be banished from Norfolk Island.
Davefoc/Wikimedia Commons, CC BY-SA

Lori Lach, James Cook University

Amid all the usual items we expect to see in the federal budget was one that raised eyebrows: A$28.8 million for three ant eradication programs.

Yet amid the inevitable media puns about the government “upping the ant-e”, we should note that these funds are for the continuation of existing programs that have already attracted significant funding and made substantial progress. Stopping now would have meant previous funding was wasted.

The funds will go a long way towards protecting Australia’s economy and environment from the damage wrought by invasive ants. But despite the apparent cash splurge, it nevertheless falls short of what is really needed.

Of the $28.8 million, $18.3 million was for the National Red Imported Fire Ant Eradication Program. These funds are part of a $411 million, ten-year program begun in 2017 to eradicate red imported fire ants from southeast Queensland, the only place they are found in Australia.




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Removing these pests will avoid an estimated $1.65 billion in total costs to 19 different parts of the economy. With previous funding, the program eradicated these ants from 8,300 hectares near the Port of Brisbane, making it the world’s largest ant eradication to date.

The Yellow Crazy Ant Eradication Program was allocated $9.2 million over three years. Yellow crazy ants have caused a cascade of ecological effects on Christmas Island, and at their peak abundance temporarily blinded a Queensland cane farmer with their acid spray.

The Wet Tropics Management Authority, which runs the program, had requested $6 million per year for six years to continue removing the ant from in and around the Wet Tropics World Heritage Area. The federal funding is $3 million short of this, and the authority is still waiting to hear whether the Queensland government will provide the remainder.

Since 2013, the program has received $9.5 million from the federal government (and $3 million from the Queensland government). No yellow crazy ants have been observed in about half of the target area in more than a year. A yet-to-be published analysis estimates the benefit-cost ratio for the program as 178:1.

“It’s a mop-up operation… we’ve got our foot on the throat of this thing.”

A further $1.3 million was allocated to the Argentine Ant Eradication Strategy on Norfolk Island in the South Pacific. Argentine ants have invaded places with Mediterranean-type climates all over the world, including southwestern Western Australia and parts of southern Australia, and become firmly established. But unlike those areas, the population on Norfolk Island is still considered small enough to be eradicable, and federally funded efforts to remove them began in 2010.

Yellow crazy ants in Queensland and Argentine ants on Norfolk Island directly threaten World Heritage Areas. The ants can have significant impacts on native birds, mammals, insects, reptiles, amphibians, and plants. Getting rid of them is important for meeting Australia’s international obligations to protect World Heritage sites.

What is ant eradication?

Ant eradication means removing all individuals of a particular ant species from a given area.

The first step is to define the extent of that area. Depending on the species, this may involve visual searches and/or placing lures such as sausages, cat food, or jam to attract the ants. The public can help by notifying relevant authorities of unusual ants in their gardens, and by not transporting materials that have ants on them.

The second step is treatment. Currently, the only way to eradicate ants is with insecticidal baits. Ants’ social structure makes this particularly challenging: killing the queens is vital for eradication, but queens typically stay sheltered in the nest – the only ants we see out foraging are workers.

Some of the most problematic ant species can have hundreds of queens and tens of thousands of workers per nest. They can reach extraordinarily high densities, partly because invasive ant species, unlike most of our native ant species, do not fight one another for territories.

Yellow crazy ants, proving it is possible to feel sorry for a cockroach.
Bradley Rentz/Wikimedia Commons, CC BY-SA

Beating ants means turning their biology against them. Bait needs to be attractive enough for workers to bring back to the colony and share, but not so deadly that they die before they get there. (And yes, this means if you’re spraying foraging ants in your kitchen you won’t get rid them for good, because the queens are somewhere hidden, laying more eggs and making more ants.)

Most ant eradication programs take three to four years to fine-tune their baiting regime because of a multitude of factors that need to be considered, such as seasonal changes in ant foraging behaviour and food preference, and the desire to avoid harming non-target species. Typically, two to six treatments are required, depending on the ant species, the size of the area, and the habitat type.

Beating the 1%

The hardest part of ant eradication is the end-game. Getting rid of the final 1% requires first finding them. This may mean painstaking searches through hundreds of hectares of bushland and residential areas, and the placement of hundreds of thousands of lures. Detector dogs can be very helpful, but they cannot be used in all environments and also need substantial resources for training, handling, and maintenance.

Ironically, it is at this stage that public and political support for eradication programs is most likely to wane, because ant numbers are too low to be seen as a threat to the public, economy or environment. Yet it is vital not to stop now, or else the remaining 1% will simply build up their numbers again. Experienced staff are also lost when programs suffer cuts or delays in their funding.




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Disappointingly not mentioned in the budget was funding for eradicating electric ants. Like red imported fire ants, electric ants have a painful sting, and when left to multiply will eventually turn gardens and swimming pools into no-go zones. They also pose a significant threat to native animals such as the southern cassowary, and can blind animals as large as elephants.

They are currently only found in the Cairns region. The National Electric Ant Eradication Program, funded by federal and state governments, ran from 2006 until 2017 and had likely reduced numbers down to that last 1%. The program has been running on state funding with reduced staff since then, but several new detections in the past three months demonstrate the cost of the gap in funding.

In those inevitable “federal budget winners and losers” lists, invasive ants have found themselves firmly in the losers column for 2019. But it’s worth remembering that most of the world’s roughly 15,000 known ant species provide vital services for the functioning of our ecosystems.

They aerate soil and redistribute its nutrients, protect plants from herbivores, disperse seeds, and repurpose dead organisms. They may even help slow down the spread of those pesky invasive ants that are much less friendly.The Conversation

Lori Lach, Associate Professor, James Cook University

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

Stowaway mozzies enter Australia from Asian holiday spots – and they’re resistant to insecticides



File 20190320 93051 1rj4pog.jpg?ixlib=rb 1.1
We might not be able to use common insecticides to kill mosquitoes that arrive from other countries.
from www.shutterstock.com

Tom Schmidt, University of Melbourne; Andrew Weeks, University of Melbourne, and Ary Hoffmann, University of Melbourne

Planning a trip to the tropics? You might end up bringing home more than just a tan and a towel.

Our latest research looked at mosquitoes that travel as secret stowaways on flights returning to Australia and New Zealand from popular holiday destinations.

We found mosquito stowaways mostly enter Australia from Southeast Asia, and enter New Zealand from the Pacific Islands. Worse still, most of these stowaways are resistant to a wide range of insecticides, and could spread disease and be difficult to control in their new homes.




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Secret stowaways

Undetected insects and other small creatures are transported by accident when people travel, and can cause enormous damage when they invade new locations.

Of all stowaway species, few have been as destructive as mosquitoes. Over the past 500 years, mosquitoes such as the yellow fever mosquito (Aedes aegypti) and Asian tiger mosquito (Aedes albopictus) have spread throughout the world’s tropical and subtropical regions.

Dengue spread by Aedes aegypti mosquitoes now affects tens to hundreds of millions of people every year.




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Mosquitoes first travelled onboard wooden sailing ships, and now move atop container ships and within aircraft.

Adults in your luggage

You probably won’t see Aedes mosquitoes buzzing about the cabin on your next inbound flight from the tropics. They are usually transported with cargo, either as adults or occasionally as eggs (that can hatch once in contact with water).

It only takes a few Aedes stowaways to start a new invasion. In Australia, they’ve been caught at international airports and seaports, and in recent years there has been a large increase in detections.

Aedes aegypti mosquito detections per year at Australian international terminals – passenger airline terminals in white; seaports or freight terminals in black.
Tom Schmidt, Author provided



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In our new paper, we set out to determine where stowaway Aedes aegypti collected in Australia and New Zealand were coming from. This hasn’t previously been possible.

Usually, mosquitoes are only collected after they have “disembarked” from their boat or plane. Government authorities monitor these stowaways by setting traps around airports or seaports that can capture adult mosquitoes. Using this method alone, they’re not able to tell which plane they came on.

But our approach added another layer: we looked at the DNA of collected mosquitoes. We knew from our previous work that the DNA from any two mosquitoes from the same location (such as Vietnam, for example) would be more similar than the DNA from two mosquitoes from different locations (such as Vietnam and Brazil).

So we built a DNA reference databank of Aedes aegypti collected from around the world, and compared the DNA of the Aedes aegypti stowaways to this reference databank. We could then work out whether a stowaway mosquito came from a particular location.

We identified the country of origin of most of the Aedes aegypti stowaways. The majority of these mosquitoes detected in Australia are likely to have come from flights originating in Bali.

Here’s where the Aedes aegypti mozzies come into Australia and New Zealand from.
Tom Schmidt, Author provided

Now we can work with these countries to build smarter systems for stopping the movement of stowaways.

As the project continues, we will keep adding new collections of Aedes aegypti to our reference databank. This will make it easier to identify the origin of future stowaways.

New mosquitoes are a problem

As Aedes aegypti has existed in Australia since the 19th century, the value of this research may seem hard to grasp. Why worry about invasions by a species that’s already here? There are two key reasons.

Currently, Aedes aegypti is only found in northern Australia. It is not found in any of Australia’s capital cities where the majority of Australians live. If Aedes aegypti established a population in a capital city, such as Brisbane, there would be more chance of the dengue virus being spread in Australia.

The other key reason is because of insecticide resistance. In places where people use lots of insecticide to control Aedes aegypti, the mosquitoes develop resistance to these chemicals. This resistance generally comes from one or more DNA mutations, which are passed from parents to their offspring.




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Importantly, none of these mutations are currently found in Australian Aedes aegpyti. The danger is that mosquitoes from overseas could introduce these resistance mutations into Australian Aedes aegpyti populations. This would make it harder to control them with insecticides if there is a dengue outbreak in the future.

In our study, we found that every Aedes aegpyti stowaway that had come from overseas had at least one insecticide resistance mutation. Most mosquitoes had multiple mutations, which should make them resistant to multiple types of insecticides. Ironically, these include the same types of insecticides used on planes to stop the movement of stowaways.

Other species to watch

We can now start tracking other stowaway species using the same methods. The Asian tiger mosquito (Aedes albopictus) hasn’t been found on mainland Australia, but has invaded the Torres Strait Islands and may reach the Cape York Peninsula soon.

Worse still, it is even better than Aedes aegypti at stowing away, as Aedes albopictus eggs can handle a wider range of temperatures.

A future invasion of Aedes albopictus could take place through an airport or seaport in any major Australian city. Although it is not as effective as Aedes aegypti at spreading dengue, this mosquito is aggressive and has a painful bite. This has given it the nickname “the barbecue stopper”.

Beyond mosquitoes, our DNA-based approach can also be applied to other pests. This should be particularly important for protecting Australia’s A$45 billion dollar agricultural export market as international movement of people and goods continues to increase.




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The Conversation


Tom Schmidt, Research fellow, University of Melbourne; Andrew Weeks, Senior Research Fellow, University of Melbourne, and Ary Hoffmann, Professor, School of BioSciences and Bio21 Institute, University of Melbourne

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

Cannibalism helps fire ants invade new territory



File 20190321 93060 ig0v8t.jpg?ixlib=rb 1.1
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.




Read more:
How we wiped out the invasive African big-headed ant from Lord Howe Island


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.The Conversation

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.