By Dr Catriona Nguyen-Robertson

This article follows a one-day symposium on next-generation biocontrol of invasive vertebrate pests. Speakers included: Andrew Cox (Invasive Species Council), Professor Euan Ritchie (Deakin University), Gerald Leach (Victorian Farmers Federation), Chelsea Cooke (Warreen Beek Trainee Rangers Program, Shalan Scholfield (Department of Agriculture, Fisheries & Forestry), Dr Andreas Galnznig (Centre for Invasive Species Solutions), Dr Ellen Cottingham (University of Melbourne), Dr Tanja Strive (CSIRO), Professor Paul Thomas (University of Adelaide), Dr Chandran Pfiztner (Macquarie University), Dr Agus Sunarto (CSIRO), Dr Stephen Frankenberg (University of Melbourne), Professor Dan Tompkins (Predator Free 2050), Professor Ben Phillips (University of Melbourne), James Trezise (Invasive Species Council) and Rita Hawkes (RSPCA).

Australia is home to many plants and animals that have been introduced since Europeans arrived. Some have become invasive, multiplying and spreading through the environment rapidly to the point that they are destructive. They threaten the persistence of threatened native species and are a burden on our health, economy, and society.

Many introduced species have become so established in Australia that it is now considered almost impossible to eradicate them. In fact, we are sometimes oblivious to the pets we love to care for or the garden plants we tenderly water can be catastrophically dangerous to Australia’s unique biodiversity if allowed to propagate in the wild. (Editor’s note – disturbingly, many people don’t seem to know what is – and is not – a native animal, much less the damage that pest exotic species are causing to Australia’s landscapes and ecosystems. Consider the pervasive imagery of deer and reindeer in our homes and workplaces, particularly as we approach the Christmas season.)

When walking through parks and other grassy areas in Melbourne with friends, I have heard them exclaim “what a cute bunny” when one hops across our path. However, I am never as excited; the European rabbit is the top pest impacting Australia’s threatened plants and animals. Reading about why rabbits were brought over, it is not such a surprising story: 13 rabbits were brought to Australia for hunting on one estate – from which they quickly proliferated across the landscape. It became the fastest known invasion by a mammal anywhere in the world. I also see many cats out and about in my neighbourhood, knowing that each roaming pet cat kills 110 native animals per year on average.

As someone who has always lived in the city, I have always known that invasive species were a massive problem – however, I was unaware of the immense scale of the problem.

Invasive species are not merely an environmental problem. They also cause immense economic and cultural damage. Since the 1960s, Australia has variously spent and incurred losses amounting to $390 billion due to invasive species. The problem only continues to grow, compounded by the impacts of land development, climate change and other human-driven impacts on native plants and animals, and we now face the challenge of containing the damage. Thankfully, there are many researchers and organisations who are working towards solutions.

What are invasive species?

Mr Gerald Leach, Chair of the Environment, Planning & Climate Change Committee for the Victorian Farmers Federation, presenting to the Royal Society of Victoria on the “On Farm Costs of Invasives.”

When we hear the term ‘invasive species’, we may think of rabbits and cane toads. Perhaps feral cats and foxes also come to mind. While cats and foxes alone kill over 2.6 billion native animals each year, the problem is much greater than these well-known offenders – although, for the purposes of this article, only invasive vertebrates are discussed.

Feral animals steal the burrows of native animals, prey on native animals and degrade land and water through overgrazing in competition with livestock and native herbivores. They are a detriment to landscapes and agriculture. Farmer and industry representative Gerald Leach outlined how feral animals impact his land and livestock. Farmers deal with a long list of invasive species, investing money, time and effort to prevent feral animals from destroying soils, crops and livestock. Accompanying this economic impact is the great mental health cost for farmers like Gerald who see their stock repeatedly attacked, their landscapes damaged, and livelihoods destroyed.

Another issue is the ever-increasing damage of invasive species to Indigenous people’s connection to Country. The Yugul Mangi Rangers in Southeast Arnhem Land are struggling to control feral animals, the worst offenders being pigs and cane toads. Pigs disturb freshwater wetlands and dig up edible plants, and cane toads kill small native animals like goanna and quolls that were also once food. These bush foods have now become rare, along with the traditional practice of harvesting them.

Elsewhere in the Northern Territory – in fact, covering 40% of it – feral camels eat native plants and destroy important Aboriginal cultural sites. The Ghan Railway was built with the help of camels, who travelled 200-300 km per day and lasted days without water. But then the camels were set loose once construction was complete. Trust for Nature Conservation Officer and Arrernte woman Chelsea Cooke, spoke about how heartbreaking it was to see cultural sites and waterholes decimated by the growing population of feral camels – particularly as her cultural heritage is also drawn from the Afghani cameleers who have traditionally nurtured this introduced species.

Most of the environmental impacts on threatened species in Australia are caused by 267 invasive species, of which 230 are non-native to Australia. Native species can also become pests when they are introduced to regions and habitats where they are not endemic, or lack natural predators to control numbers. Invasive vertebrate species alone have widespread impacts on ecosystems, agriculture, and cultural activities throughout Australia.

What can we do about invasive species?

While it would be desirable to completely rid the Australian continent of the worst offenders, it is simply not feasible in most cases. Complex interactions between native and invasive species can complicate decisions and actions around control. For example, in many areas, feral rabbits are a major food source for foxes and feral cats; reducing the number of rabbits may therefore mean that foxes and cats turn to native animals instead, while reducing the predators means less pressure on the rabbits. It is also difficult to ensure that an invasive species cannot easily re-invade.

Mr Andreas Glanznig, CEO for the Centre for Invasive Species Solutions, advocates for innovation pipelines: putting in place the capacity to deal with invasive species through biocontrol strategies over 20 years or longer. Short-term solutions simply will not work as an invasive population will often bounce back quickly, wasting time, effort and resources.

Invasive species management therefore focuses on minimising their impacts as cost effectively as possible. Given community concerns for animal welfare, pest control programs must also be humane and have minimal impact on non-target species. To this end, there is great promise in the development of new and emerging biological control strategies.

Biocontrol measures are never a silver bullet, as they are not guaranteed to be effective for every single animal. It is therefore imperative to have multiple bullets.

Rabbits

For decades, CSIRO has been leading an ongoing battle to ease the enormous detrimental economic, environmental, and social impacts of rabbits. In 1950, CSIRO released the world’s first vertebrate pest biocontrol, myxoma virus, killing 99.8% of infected rabbits. But as we often see with evolution, rabbits became resistant. In 1996, rabbit haemorrhagic disease virus was released in Australia, reducing rabbit numbers to very low levels. Nearly 20 years later, an additional strain was identified that further curtailed wild rabbit populations.

Dr Tanja Strive is the Principal Research Scientist for CSIRO Health & Biosecurity, working hard to boost viruses that already exist and identify new pathogens that could be used to keep rabbit numbers down. She also looks to novel genetic approaches to maximise the outcome of rabbit biocontrol operations.

Cats

Many of us love our cats, and therefore do not necessarily want to consider biocontrol measures to manage them. However, feral cats kill 75 million native animals every night, and we urgently need an intervention.

Dr Ellen Cottingham at the University of Melbourne has developed an innovative approach: immunocontraception, using a cat’s own immune system to induce a contraceptive effect. This does not lead to the death of animals; rather, it prevents an excessive number from being born in the first place. Immunocontraception has previously been used to curb African elephant overpopulation without any behavioural side effects. Now Ellen wants to develop this technology for feral cats.

The technology starts off similarly to vaccination: select a target gene involved in reproduction, then deliver the gene within a viral vector to “vaccinate” the cats. Their cells will then produce the reproductive protein, but now in the context of a viral infection – it will appear as an invader to the immune system. Cats will then raise an immune cell army to target the reproductive protein to wipe it out, reducing their own fertility. This approach will be specific for feral cats, as pets should already be vaccinated against the virus used as a vector (feline herpesvirus); and as Ellen points out, we should be sterilising our pet cats anyway. By using cats’ own immune systems to reduce their fertility, this could ensure that the feral population does not continue to grow uncontrollably.

Fish

Swimming in our waterways, pest fish such as the European carp and tilapia outcompete native fish for habitat and food. Their feeding and nesting habits can also directly degrade water quality. While the use of a virus to curb pest rabbits is familiar to many, perhaps less familiar is the application of biocontrol to fish. Dr Agus Sunarto is investigating the possibility of using the tilapia lake virus, which kills tilapia quickly without impact any native fish. He is ensuring that researchers have approaches in place to test the safety and efficacy of the tilapia lake virus – and any other biocontrol agent.

Taking a different approach, Postdoctoral Fellow Dr Chandran Pfitzner from Macquarie University is genetically engineering fish. Genetically modified male and female “stock fish” are engineered to only generate male offspring. Furthermore, when they mate with pest fish in the wild, their offspring will be completely unviable. By ensuring that reproduction of carp in a stock results only in viable males and no females, the population will eventually crash as they can no longer reproduce without both sexes.

Gene drives

Gene drive applications are being increasingly considered in biocontrol. They can provide significant positive benefits, especially where alternative methods are ineffective, damaging to the environment and/or costly. With normal genetic inheritance, the chance that a version of a gene will be passed on from parent to offspring is 50-50. Gene drives, which are self-propagating genetic elements, boost these odds and are preferentially passed on. If the genetic element happens to be a mutated version of a reproductive gene to decrease fertility, it will be spread rapidly through a population.

Researchers are investigating the use of gene drives to tackle rodents, cane toads, carp, foxes, and rabbits. However, given that the field is still somewhat in its infancy, other researchers, such as Dr Stephen Frankenberg, need to ensure that we will have total control. For example, using a genetic modification in two separate genes, rather than one, could help prevent the spread of the gene drive to non-target animals – similar to two-factor authentication on our phones when we sign into accounts on our computers.

As gene drives are in an early stage of development, the discussion around their possible consequences and risks are still largely speculative. When considering implementing gene drives, it is important to model the process to reduce uncertainties. Professor Paul Thomas has modelled a gene drive that makes alterations to a female fertility gene in mice to render them infertile. His team used modelling to determine that a release of 256 mice with the gene drive into a population of 200,000 on an island would eradicate the population in about 25 years. This is welcome news to farmers like Gerald, who hope for a curbing of invasive mice numbers.

What are the barriers to seeing these implemented?

As with any area of research, funding is a large barrier. Scientists can only research and develop solutions to tackle these problems so long as they have the funds to do so. But once we get there, for any research breakthroughs, concepts, and applications, we must consider underpinning knowledge & socio-political contexts. As Professor Dan Tompkins points out, even if we develop a great way to tackle invasive pests, it will not get off the ground if there is public resistance.

Mr James Trezise works with the messy and highly contested space of public opinion concerning invasive species every day as the Conservation Director of the Invasive Species Council. The cane toad continues to loom large in our minds almost ninety years following its disastrous introduction to the Australian continent, meaning a strong legacy of further, successful biological controls of pests have not succeeded in shifting public perceptions on the trustworthiness of science-backed interventions.

James emphasises that the concept of “social license” does not mean political power, nor the ability to affect change. Essentially our main barrier to popular support for intervention with invasive species is a lack of understanding about the scale and urgency of the threat to our environment and assessing who is simply waiting for clarity before offering support or opposition.

Despite CSIRO’s legacy of the cane toad, James tells us the most trusted messengers in Australian society are members of the scientific community. Communication is therefore so important. People have power. One of the best ways to reduce invasive species in Australia is through education and awareness. As mentioned previously, many people are unaware that certain species are in fact pests. Invasive species is a poorly understood issue, yet Australians do care about wildlife extinction. Without effective communication, we won’t see change.

Video

You can view all three sessions of the Next-Generation Biocontrol of Invasive Vertebrate Pests symposium on the Society’s YouTube channel: each tackle ‘The Problem,’ ‘The Technologies’ and ‘The Caveats’ in succession. The playlist is available from https://bit.ly/next-gen-biocontrol or you can watch using the player below.