Australia’s cane toads evolved as cannibals with frightening speed

The list of ‘deadly animals in Australia’ just got a little weirder. The cane toad, a toxic, invasive species notorious for devouring anything it can fit in its mouth — household rubbish, small rodents and even birds — has become highly cannibalistic in the 86 years since it was introduced to the continent, according to a new study. Its counterpart in South America, where cane toads originated, is far less cannibalistic.

The discovery could help researchers to understand the evolutionary underpinnings of how this uncommon and extreme behaviour emerges. Scientists have seen cannibalism evolve in species before, says Volker Rudolf, a community ecologist at Rice University in Texas, who studies the phenomenon. But what’s exciting about this work, he says, is that the researchers are almost seeing it “develop in front of their eyes”, given that the behaviour arose in less than a hundred years — the blink of an eye by evolutionary standards.

“These toads have gotten to the point where their own worst enemy is themselves,” says Jayna DeVore, an invasive-species biologist at Tetiaroa Society, a non-profit organization in French Polynesia, and a co-author of the study, which was published on 23 August in Proceedings of the National Academy of Sciences of the United States of America1. Scientists estimate that there are well over 200 million of the amphibians in Australia. They have become so abundant, says DeVore, that they face more evolutionary pressure from each other, as they compete for resources, than from anything else in Australia.

Tadpole terror

Farmers first introduced about 100 cane toads (Rhinella marina) to Australia from their native range in South America in 1935 to control cane beetles (Dermolepida albohirtum), which were wreaking havoc on sugarcane plantations. The giant toads failed to knock down the beetle populations, but they succeeded in epically multiplying. Because of their highly poisonous skin, which is coated in bufotoxins, they had no natural predators and went on to invade large swaths of the northern and eastern parts of the country.

Although adult cane toads are fearsome — they grow up to 25 centimetres in length — it’s their tadpoles that are usually the cannibals. Multiple tadpoles together can gobble more than 99% of the hatchlings that emerge from the tens of thousands of eggs in a single clutch2.

DeVore and colleagues were curious to see whether the cannibalistic behaviour was common across all cane toads, or if it was due to how invasive the Australian ones are. So they collected cane toads from Australia and from French Guiana, and bred them to produce hatchlings and older tadpoles. The team then exposed a single tadpole to 10 hatchlings from its group — either from Australia or South America — hundreds of times and found that invasive Australian tadpoles were 2.6 times as likely to cannibalize hatchlings as native South American ones.

Researchers have long known that the Australian tadpoles are attracted to the hatchlings because of the scent of the younger animals’ toxic skin. “You’ll get this huge avalanche of thousands and thousands of tiny cane-toad tadpoles coming toward this chemical,” says Rick Shine, an evolutionary biologist at the University of Sydney in Australia, and a co-author of the study. DeVore, Shine and co-workers saw this play out in their experiments: the Australian tadpoles were nearly 30 times as likely to swim towards a trap containing hatchlings as an empty trap, and the South American tadpoles showed no preference for either.

Although the speed with which the toads evolved this behaviour is impressive, the team was even more surprised by how fast the animals evolved a defence to protect against it. The researchers found that when invasive Australian hatchlings shared a tank with caged, older tadpoles from the same group, the hatchlings were more likely to have a shorter developmental period than that of the South American hatchlings. Older tadpoles don’t tend to eat older tadpoles — so the toads might have evolved to speed up their hatchling phase, the researchers found. This would limit the amount of time they spend vulnerable to cannibalism, even if the adaptation eventually stunts their growth, says DeVore.

Roshan Vijendravarma, an evolutionary biologist at the Curie Institute in Paris, who has studied cannibalism in fruit flies, says the differences between the invasive and native toads’ behaviour probably have a genetic basis, given how extreme they are and how quickly they evolved over relatively few generations of toads.

Shine and his colleagues think this idea is worth exploring and are studying it now. Although there are still mysteries around the cane toads’ cannibalistic tendencies, one thing is for certain, says Shine: “The cane toads that are currently hopping across Australia are extraordinarily different animals from the ones that were first taken out of the native range.”

Destructive coconut rhinoceros beetle a ‘stone’s throw’ from Australia as it spreads through Pacific

Australia’s sugar, pineapple, mango, and coconut oil industries are facing a major threat from a destructive pest beetle sitting on the nation’s doorstep.

The coconut rhinoceros beetle has bulldozed its way across the Pacific in just a few years and is now in Papua New Guinea, University of Queensland researcher Dr Kayvan Etebari warned.

“If it gets into Australia, coconut oil palms and many other palms found in the forest and in home gardens will be at risk,” Dr Etebari said.

“If it gets into Australia, coconut oil palms and many other palms found in the forest and in home gardens will be at risk,” Dr Etebari said.

It has been a year since another invasive pest, the fall armyworm, was first detected at Bamaga at the tip of far north Queensland and has since devoured crops across most states and territories.

Dr Etebari said the fall armyworm came down the island chain from PNG. 

“Last week it got into Tasmania,” he said.

The coconut rhinoceros beetle, a native of South-East Asia, has been in Samoa, Fiji, and Tonga for a century, but was successfully controlled by a virus for the past 50 years.

However, that biological control is now failing.

Stone’s throw away

Central Queensland horticulturalist Neil Fisher has been watching with growing concern the beetle’s rapid march from the South Pacific across to Guam and Hawaii to Vanuatu, New Caledonia, and Solomon Islands.

“The move through Papua New Guinea has been quite swift and we’ve seen large-scale coconut plantations and oil palm plantations being destroyed,” he said.

“Our border security is the Torres Strait and it’s only a matter of kilometres, just a stone’s throw from Papua New Guinea into north Queensland.”

A coconut rhinoceros beetle with a number on its back perches on a blue-gloved finger.
The coconut rhinoceros beetle was stopped in its tracks by a virus introduced 50 years ago, and it stayed put — until now.(Supplied: Forest and Kim Starr)

Councillor Fisher, who is also the deputy mayor of the Rockhampton Regional Council, said it was a concern shared with council colleagues in Cairns.

“There are miles of coconut-lined beaches to the north of Cairns and to lose those would see erosion coming back. You could lose two or three kilometres of actual shoreline,” Cr Fisher said.

The beetle causes damage by boring into the plant’s stem and feeding on the sap, damaging the developing leaves.

The plant will then be defoliated and will die during a heavy infestation.

The beetle lays eggs in decaying matter and then moves on.

“We knew it was a risk, but it wasn’t until it got into large horticulture and agriculture areas in Hawaii that suddenly the red flags went up,” Cr Fisher said.

He said Hawaii had similar horticulture and plant culture to Australia.

On top of the obvious economic threat to the country’s $2 billion sugar industry and $53 million pineapple industry, Cr Fisher said the beetle could pose a threat to other plants.

“If it’s in pineapples, what about bromeliads? It’s an up-and-coming collector choice for gardeners. And if it can get into sugar cane, what is the risk to other canes and bamboos?” he said.

Cr Fisher said it was important to work with universities to find a new biological control to keep the insect at bay.

COVID-19 similarities 

Dr Etebari and his team at UQ are studying why the virus is no longer controlling the beetle and their findings would be critical to managing the pest if it got a foothold in Australia.

“The question is how do we stop it? And what’s gone wrong with the control that’s been effective for the past five decades?” Dr Etebari said.

The researchers discovered that there have been several new waves of beetle invasions, not one as previously thought, as well as different types of beetles.

They also found there were variations to the beetle virus which was originally sourced from Malaysia.

“It’s similar to how other scientists spot different strains of COVID-19. We are detecting variations in the beetle virus in the Pacific,” Dr Etebari said.

“In our case the problem is more complicated because there are different types of beetles and different strains of the beetle virus.”

Their next step was finding out how the virus variations behaved in the different beetles and how that could be used to control them.

Dr Etebari said it was important for Australia to help its Pacific neighbours to tackle the pest, not just for economic reasons, but also humanitarian.

“It’s a serious threat to livelihoods across the Pacific islands as the coconut tree provides essential resources like food, copra, building material, and the coastal protection for more than five million vulnerable people,” he said.

A Department of Agriculture, Water and the Environment spokesperson said it was working with biosecurity counterparts in PNG and Solomon Islands to track and monitor the spread of the new beetle strain.

The department was also actively monitoring the spread of the beetle strains through PNG, particularly in the Western Province and PNG Treaty Village areas bordering Australia’s northern Torres Strait Islands. 

The spokesperson said the department was also supporting regional initiatives that were dealing with the coconut rhinoceros beetle.

Is genetically modified corn the answer to fall armyworm?

It’s a tiny caterpillar that’s difficult to detect, but for more than a year it’s been having a massive impact on crops in Australia, especially corn. 

Fall armyworm (FAW) has infiltrated six states and territories and is so hard to control farmers are whispering about a method that’s been off the table for almost two decades — genetically modified (GM) corn.

Maize Association of Australia chairman Stephen Wilson said questions were being raised about whether GM corn could manage the armyworm incursion.

“Anecdotally, I am hearing from the field farmers saying we need GM to help us control the insect,” he said. 

“It’s a major discussion point for the industry as a whole because for the last three decades we, as an industry, as the Maize Association, have been working uniformly to say we do not need GM in Australia.” 

Lessons from the US 

Since arriving in Australia in February 2020, fall armyworm has been detected in Queensland, the Northern Territory, Western Australia, New South Wales, Victoria and, most recently, in Tasmania. 

Fall armyworm is native to the United States, where it has devastated multiple agricultural crops, but growers there have different tools to fight it. 

North Carolina State University professor and extension specialist Dr Dominic Reisig said in their industry, corn was genetically modified to produce insecticidal proteins that naturally occured in a bacteria found in soil. It is known as BT corn.

Dr Reisig said while it was not specifically designed to treat FAW it had had an impact. 

“It was first commercially planted in 1996 but that particular crop that was planted did not control fall armyworm,” he said.

“So it wasn’t until different BT toxins were introduced that we really started to see fall armyworm control. 

“But because it’s a sporadic outbreak pest throughout the US it wasn’t like a huge, earth-shattering moment when we were able to control fall armyworm.” 

Are GMO crops the silver bullet? 

According to Dr Reisig, treating FAW across ag industries was a multi-pronged approach with insecticides and a GM crop. 

He said in corn the pest could infest a crop in different stages of its development. 

“Once it gets into the whirl it’s very difficult to control,” he said. 

“But the good thing is when it attacks in those (earlier) stages it’s not that damaging to yield — so the corn looks really bad but it usually pops out of it and it’s not a problem. 

“If fall armyworm attacks later in the season when maize has an ear, then it’s a problem. 

“Once it’s inside that ear you can’t control it and then it’s a really damaging pest in terms of yield and it’s really difficult to control with insecticides so BT (corn) is the way to go.”

He said insecticides were able to control the pest in other crops like soya beans or vegetables because the plants were structured differently.

Weighing up the losses 

Australia only grows three GM crops — cotton, safflower and canola. 

Corn has remained GM-free and, as a consequence, the industry has been able to access different markets including Japan and Korea. 

“End users such as snack food and cornflake breakfast cereal manufacturers have told us the whole time they do not want GM in their raw materials,” Mr Wilson said. 

“It would impact on both the export market and also on all the domestic markets — everything from dairy cows utlising the maize as grain or silage right through to beef cattle and right through to human consumption. 

“It’s a major, major, major impact that would need to be agreed to by all sectors of the industry.” 

A person opens a corn's covering to check if it's ripe.
Australia has been able to access multiple international markets as the corn grown here is GM free.(Pexels: Frank Meriño)

He said any trial would be complicated.

“You have all the regulatory issues of actually bringing germplasm into the country, you have the quarantine issues of having the facilities that could handle the GM product, then you’ve got the issues of field testing,” he said. 

“It would be a long, drawn-out process and we’d have to consider the impact on the industry as a whole because it’s very hard, if not impossible, to have part-GM, part-non-GM. 

“It’s a very expensive process and it makes the non-GM corn being in the minority a very expensive product that people have to pay a premium for.” 

In a statement, a spokesperson from the Federal Department of Agriculture, Water and the Environment said genetically modified maize seeds may only be imported into Australia under an import permit issued by the department, but that no applications had been made. 

Insecticide differences for fall armyworm

NEW research indicates there are variable levels of sensitivity to some insecticides between populations of fall armyworm (FAW) in different geographical areas of Australia.

FAW is a highly migratory, invasive pest that was first reported in Australia in February 2020 and quickly established across parts of northern Australia’s tropical and sub-tropical regions, including northern Queensland, the Northern Territory, and northern parts of Western Australia.

It has been detected in southern WA, New South Wales and Victoria.

The new findings are from two complementary projects, one being a comprehensive research project into FAW’s insecticide sensitivities and genetic make-up being led by Australia’s national science agency CSIRO, with co-investment by the Australian Centre for International Agricultural Research, the Grains Research and Development Corporation (GRDC), Cotton Research and Development Corporation, FMC Australasia and Corteva Agriscience.

CSIRO researcher Wee Tek Tay said the research provided evidence that two geographically separated populations – a WA population from Kununurra in the Kimberley region and a north Queensland population from Walkamin in the Tablelands region – showed variable levels of sensitivity to insecticides.

“Geographic variability in insecticide responses is not unexpected and is commonly observed in the closely related species Helicoverpa armigera,” Dr Tay said.

“The findings don’t necessarily indicate distinct genetic differences in the populations – results of genomic analyses are pending – but they do have implications for growers trying to manage FAW in the field.”

In the absence of a FAW population susceptible to insecticides, bioassays were conducted using H. armigera as a comparison.

Colonies of insects were raised in the laboratory for the tests using individuals sampled from limited areas.

Therefore, they are not necessarily representative of the population in that region, so some caution is needed in interpreting the findings.

NSW Department of Primary Industries (DPI) researcher Lisa Bird said an independent and complementary study of FAW susceptibility in five populations from north Queensland and one population from Kununurra also revealed geographic differences in sensitivity to some synthetic insecticides.

Both the CSIRO and the DPI studies found that FAW populations were between 50 and 150 times less sensitive to the pyrethroid alpha-cypermethrin compared with susceptible strains of H. armigera.

Both researchers found similar levels of variability in sensitivity to methomyl, ranging from three to 11 times less sensitive, in populations from north Queensland compared with susceptible strains of H. armigera.

In contrast, CSIRO found its WA population to be 52 times less sensitive.

Relative tolerance to indoxacarb was found in all FAW populations tested.

Populations from north Queensland were between 11 to 63 times more tolerant to indoxacarb than the susceptible reference strain of H. armigera.

Both researchers included a Kununurra population, with the CSIRO population being 208 times more tolerant and the DPI population being 61 times more tolerant.

This highlights the variability of FAW’s response to an insecticide even from within the same general region.

It is possible FAW has a natural level of tolerance to indoxacarb.

While chlorantraniliprole sensitivity was found to be similar in north Queensland populations compared with H. armigera, the WA colony tested by CSIRO was 15 times less sensitive.

However, there may still be significant variability in sensitivity to this chemistry within the Kununurra region and further work is needed to document the full range of naturally occurring geographic variability between Australian FAW populations.

Sensitivity to emamectin and spinetoram was found to be similar in all FAW populations and H. armigera.

GRDC biosecurity manager Jeevan Khurana said these results provided evidence that geographically different FAW populations in Australia can vary in their responses to insecticide.

“This new knowledge helps to guide insecticide choice,” Dr Khurana said.

“As always, growers are encouraged to judiciously select and rotate products to reduce selection pressure.

“While these studies don’t directly reflect field rates and conditions, it is important for growers to consider insecticide sensitivity when making decisions about product choice.

“Always use the full rate as stated on the label or permit.

“Where a rate range is specified, such as on current FAW permits for indoxacarb and chlorantraniliprole in maize, it is recommended to use the higher rate in accordance with the permit instructions.

“In addition, particular attention should be made to targeting early instar stages (hatchlings to second instar) before FAW entrenchment in the whorl or cobs can occur, and spray coverage (water volume, spray quality etc) should be optimised to ensure the larvae are receiving a lethal dose of the insecticide.”

Pest alert as FAW marches into cane

Cane growers and service providers are being urged to be on the lookout for signs of fall armyworm, following the first confirmed report of the pest in sugarcane.

Identified in a crop on the Atherton Tablelands late last month, the occurrence is thought to be as a result of a heavily-infested maize crop that bordered the cane.

Vigilance is key to managing the threat and responding appropriately, with growers and service providers encouraged to be on the lookout, particularly in blocks near corn/maize or other affected crops.

Early detection coupled with accurate diagnosis will assist with effective pest management decisions for affected crops.

Agrisciences Queensland (DAF) is the main point of contact for identification of potential fall armyworm and they can be contacted on 13 25 23.

The pest is now considered established in Australia, following detection at several sites including the NT, WA, New South Wales and recently in Victoria.

The fall armyworm page on the Sugar Research Australia website has a range of resources including details of the emergency use permits for Permethrin or Chlorantraniliprole to control fall armyworm

iMapPESTS program to help protect sugar cane industry

Moth borers remain one of the highest priority pests for Australian sugar cane production.

For this reason, Australian researchers have taken a proactive approach to clarifying control measures and gathering information about the pest.

While not established in Australia, there are 36 major moth pest species worldwide with seven regarded as high risk to Australia.

The nation’s geographic proximity to Papua New Guinea, Indonesia and South East Asia, where the moths live, mean Australia remains a potential migration point.

Speaking on the first day of the CaseIH Step Up conference in Bundaberg on Tuesday, Sugar Research Australia (SRA) molecular plant pathologist, Dr Nicole Thompson, said significant work had been done to forearm against the threat.

Some of this work included updating species and specimen information in databases and collections; preparing new dossiers based on this research; developing new diagnostic protocols; and updating the geographic distribution of the moth borers.

The pest was just one major concern mentioned by Dr Thompson who also spoke on iMapPESTS, a nationwide research and development collaborative initiative between Australia’s major plant industries with a goal of developing a way to rapidly monitor and report the presence of airborne pests and diseases for multiple agricultural sectors, including viticulture, grains, cotton, sugar, horticulture and forestry.

The project is about advanced surveillance technologies such as automated trapping and sampling for detecting and monitoring a wide range of endemic and exotic pests.

The project will also produce several flexible surveillance hubs with trapping technologies that can be mobilised in response to industry needs such as in response to incursions.TECH: The Sentinel is a custom-designed surveillance trailer unit designed to offer optimal sampling of airborne fungal spores and insects.

 TECH: The Sentinel is a custom-designed surveillance trailer unit designed to offer optimal sampling of airborne fungal spores and insects.

One of the pieces of equipment is the Sentinel.

The Sentinel is a custom-designed surveillance trailer unit designed to offer optimal sampling of airborne fungal spores and insects.

The Sentinel has four different air samplers: two spore samplers which are high-volume, designed to collect airborne spores; a 2m insect suction trap to monitor localised insect dynamics; and 6m insect suction trap, for monitoring of long-distance migratory insect flights.

Each air sampler is automated and collects samples into small vials for fungal spores or larger vials or larger pots for insects.

These are barcoded and read by a scanner onboard and in the labs for complete traceability.

Dr Thompson said sugarcane had many established pests and diseases such as mosaic, Fiji leaf gall, leaf scald, smut, RSD and others.

It’s hoped the iMapPESTS project will assist multiple plant industries in managing these threats.