Page last updated at 09:20 GMT, Tuesday, 9 March 2010

Hailing the arrival of alien predators

Dr Matthew Cock (Image: Cabi)
Matthew Cock

Europe is about to release its first non-native "biological control" species to curb the spread of Japanese knotweed, and about time too, says scientist Dr Matthew Cock. In this week's Green Room, he sets out the case in favour of introducing natural predators to halt the march of invasive species.

Japanese knotweed (image:PA)
It has been estimated that to manage Japanese knotweed in the UK, without successful biological control, would leave farmers, gardeners and local councils facing a bill of at least £13.5bn

For the first time in Europe, the UK government has granted approval for an insect from Japan to be released in order to control the invasive plant, Japanese knotweed.

It is the first time a "biological control" approach has been used in Europe against a plant.

But the concept is far from new, and Europe has been lagging behind other regions that have had more challenging experiences with invasive non-native species.

Japanese knotweed is a notorious plant, famed for its ability to burst through tarmac and crack concrete. Just finding it on a development site can result in huge additional costs or force developers to find alternative sites.

There have even been reports of mortgage companies refusing to lend to house buyers whose dream homes have Japanese knotweed in the garden.

In contrast, in its native range in Japan, it is just another member of the Japanese flora and it is fed upon by over 200 natural enemies, mostly plant-eating insects and plant diseases.

It is amongst these natural enemies that scientists believe the answer lies.

Counting the cost

Alien plants in the UK cost a vast amount of money and this expenditure, like the plants themselves, tends to expand at an ever-increasing rate.

Aphalara itadori (Dick Shaw/Cabi)
The Aphalara itadori is a natural predator of Japanese knotweed

It has been estimated that to manage Japanese knotweed in the UK, without successful biological control, would leave farmers, gardeners and local councils facing a bill of at least £13.5bn ($20.4bn; 15bn euros) by the end of the century.

This does not include the less obvious costs to the environment and those species that are displaced by these invaders.

The rate at which new plant invasions are happening is accelerating, as a result of factors such as increasingly mobile human populations, larger volumes of traded goods and climate change, all of which make it easier for plants to reach new areas.

Europe needs to find new ways to combat the most damaging species that become established.

The majority of these newcomers arrive without their natural enemies that can keep them in check in their native range, and this may give the exotic plants a great advantage over their new neighbours.

Biological control - the use of living organisms to control pest populations - can be thought of as a means of levelling the playing field by introducing some of the specialist natural enemies that exert control on the pests in their native range.

However, this can only be done with extreme care.

Safety first

I am an environmental scientist. The first question I ask before proposing to import a new organism is: "Is it safe?"

Cane toad (Getty Images)
The introduction of cane toads in Australia show the risks of biocontrol

Worldwide, there have been more than 7,000 introductions of biological control agents to date, about 1,300 of which were for weed biological control. The remainder was for control of invertebrate pests, mostly insects.

Of the 1,300 releases against weeds, more than 400 different agents have been released against more than 150 different target weeds over the last 110 years. Of these, only nine produced any collateral damage such as feeding on native species.

I imagine that some readers will be asking: "What about the cane toad?"

The cane toad was introduced into Australia from South America by the sugar cane industry in 1935 because it was known to eat some of the most important sugar cane pests.

There was no consideration of what the potential food range would be, or what impact the cane toads might have on the native fauna.

Not surprisingly, the toads - which grow to 20cm (8in) - turned their carnivorous attention to anything that moved. They will eat anything that they can get into their mouths.

The toads went on to become a significant problem, having a detrimental effect on native fauna, including amphibians and reptiles, as well as poisoning domestic and wild animals that tried to eat them.

Today's practitioners of biological control consider this release an ecological disaster, but one which demonstrates very clearly what can happen when a generalist predator is introduced without considering the risks that they present to species other than the target pests.

Those who regulate the introduction of biological control agents have learnt this lesson.

The methodology of science and predictability of introducing an exotic insect or plant disease for biological control has improved greatly, so that tests carried out by scientists allow good predictions to be made of what will happen in terms of safety when a weed biological control agent is introduced.

No introduction of an exotic organism can be entirely risk free, but the risk of a highly studied, specialist natural enemy feeding outside its experimentally evaluated host plant range is extremely low.

Overall, the safety record of weed biological control has been exemplary and the beneficial impact has been enormous.

Making up lost time

In the last 50 years, five countries have led the world in implementing successful weed biological control: Australia, Canada, New Zealand, South Africa and the US.


In countries like these, research into biological control is always considered and often prioritised when a new and problematic invasive plant species get out of hand.

Between them, they have tackled more than 100 weeds and achieved partial or substantial control of more than 50, with at least 30 programmes active at the moment and too early to judge.

To give just one example, the alien invasive rubber vine weed was successfully brought under control in Australia.

Introduced from Madagascar in the 19th Century, this aggressive climber was considered the single biggest threat to natural ecosystems in tropical Australia.

By the late 1980s, infestations were vast, covering 40,000 square kilometres. A rust fungus, Maravalia cryptostegiae was identified as a highly promising biological control agent and after extensive trials to assess it safety, aerial releases were made in Australia in 1995.

It is promising to be one of the most successful biological control programmes ever carried out, with heavy damage to the weed allowing regeneration of native forests. It was estimated to have provided a net value of £140m by 2005 - a saving that is growing year on year.

The UK's Department for Environment, Food and Rural Affairs (Defra) decision to grant a licence to release a biological control agent for Japanese knotweed is a milestone decision for Europe that will open the way to assess the scope for biological control of other alien weeds such as floating pennywort and Himalayan balsam, themselves very obvious and damaging invaders.

Europe can now start to catch up with the rest of the world and gain the benefits of sustainable, environmentally safe biological control of some of its most environmentally damaging alien invasive weeds.

Dr Matthew Cock is chief scientist for Cabi, a not-for-profit science-based development and information organisation

The Green Room is a series of opinion articles on environmental topics running weekly on the BBC News website

Do you agree with Dr Cock? Is biological control a cost effective way to tackle non-native invasive species? Will natural predators help curb the spread of prolific plants like Japanese knotweed? Or are the risks of introducing novel species into an ecosystem too high?

Yes, it's a good idea. I am agreed with this article. It should be developed and implemented weed management plans designed to support the efforts of local governing bodies to facilitate more effective integrated weed management on private and public lands. The goal of such plans will not be to stop the continued spread of these species but to provide additional education, research, and biological control resources to jurisdictions.
Engr Salam, LGED,Bangladesh

Public notices with photographs would help people to identify and destroy this unwanted weed.I am sure there are lots of people who unwittingly ignore and allow this plant to grow in areas of their gardens turned over to wild life.
lesley Hams, Barnes, London

Do we know for certain that Aphalara itadori feeds exclusively on Japanese knotweed? Have tests been done to see if the insect will feed on native British plants as well? We need to be 100% sure that once the insect reduces the population of knotweed, it will not move on to other plant species.
Jason Argent, Southampton, UK

using foriegn insects to control the japanese knotweed is tempting disaster! ive worked in agriculture for many years and in my experience this move is flawed. what will these insects turn their attentions to when the knotweed runs out? nature always finds a way to survive and adapt to new enviroments, what would happen if this alien insect took a fancy to potato crops?? get back to basics dig the stuff up burn it and sterilise the soil. or is hard work and common sense a flawed science these days? we have hundreds of idle hands in our prison system, chain em up an get them digging. could solve two problems at one throw!
dave horne, birmingham

I'm sure exactly the same arguments for this insect have been made in regards to other controls which have turned out to be wrong. I don't agree that this is all the result of climate change, either. Some of these plants were introduced in Victorian times.
AngieRS, Brighton, UK

It's all very well saying 'it Should be alright' - the other side of the coin 'it Might be an ecological disaster' has not benefitted from the same amount of discussion by this researcher. It is impossible to say which ancient native species of plants or trees this predatory insect might start to devour if it cannot find its favourite food. Consider, for example, the problem if it takes a liking to the English rose, or oak trees, or yew trees, or even more modern species such as potato plants - or any other number of plant species. you could wipe out an entire farm industry by introducing alien creatures - and that's the point - they are alien to our biosphere. Keep them out. The researcher has vested interests - of course he's going to say 'It Should be alright'. But it if all goes pear-shaped is he personally going to be held liable? Protect our ancient native species!
andrew young, exeter

What will they eat when the knotweed runs out? The answer is that the knotweed will never run out - it will just become rare and then most of the insects will die out looking for rare surviving clumps of the weed, since they can't survive on anything else - a bit like pandas and bamboo. So a new and much lower equilibrium will be reached, hopefully. Many native rare plants and rare insects operate in this fashion, locked in an eternal struggle for existence, but you never notice them - unless you take the trouble.
Peter Baker, Ascot

Species introduced to control invasive plants is like giving a drink to help a drunk get sober. Doesn't make sense at any level. The above article is misleading. When control species are finished eating the majority of the intended pest species they don't just die no matter how "specialized" their diets. They as the start to starve they look for other acceptable alternatives. The alternatives are usual the native plants. End of story. Invaisve species are a fact of can't stop them...trying only makes things worse. It's called evolution. Survival of the fittest. Surprised a bunch of so-called biologists could forget this point.
Sean, Aurora, Canada

It seems odd that no-one mentions Myxomatosis any more. Was it just so cruel and "effective" that no-one wants to remember this biological control method?
Martyn Wheeler, Morrisville, USA

Sometimes it is the only method that can be employed. Case in point:

The Ensign Scale (orthezia insignis) was accidentally introduced to the island of St. Helena some years ago and after failure of chemical means was brought under control through the introduction of a specific predator; a coccelid Lady Beetle (Hyperaspis Pantherina).
Robert Melbourne, Brampton, Ontario

Biological control has been used successfully in Australia in several instances, first was the introduction of a moth to feed on the invasive prickly pear, this was a raging success with almost all prickly pear wiped out, secondly was the introduction of myxomatosis and calicivirus to control rabbit populations in Australia, both these viral programs were very successful in their early years but rabbits are slowly making a comeback. Insect control is a viable alternative to manual clearing of weeds because it is essentially free once the insect has been released. Of course strict measures have to be taken to ensure that the insect only eats the target species but usually in this day and age, governments will got to great lengths to ensure that only target species are eaten. they a re a viable and economic alternative to manual clearing.
Felix Dollmann, Newcastle Australia

its all well and good having this wonderful new critter that can munch its way through knotweed, but I can't seem to find any reference anywhere on the Beeb or CABI that states whether or not anything will actually EAT this insect? we're all worried that it will decimate crops etc. but has anyone considered the fact that in several years time we may be overrun with these insects that are not being eaten by our predators due to being toxic (for example) or are killing off the predators for this very reason?
jo smith, London, UK

I have seen the devastation in New Zealand where many foreign species have been set free to the gross detriment of the local flora and fauna, and unsuccessful attempts to control one pest by introducing another, both of which turn to other food which is easier, till it is endangered, like the kiwi. The NZ countryside is awash with broom, gorse and other non-natives with nothing which limits their spread. The UK will be very lucky if this does not turn out to be another disaster pretty fast. All local creatures are [should be] in balance because they are local with local competitors, prey and hunters; interfere with this principle and all hell breaks loose. When will we learn?
Bill Otto, Kingston on Thames

I think this is an excellent idea. Biological control is often viewed in a negative light as many people hold the view that the introduction of a species into an ecosystem holds so many potential problems that they can't all be regulated for. Indeed a few case studies would support that view, for example the measures taken against the gypsy moth in the USA. However to state that is a norm or even that there is a remote danger to the ecosystems of the UK can only be said in ignorance of the facts. Hundreds of these programmes have been implemented throughout the world and provided economic benefits year in year out. To say that not all factors have been accounted for is simply an insult of the professionals behind this programme. In short I am very surprised that this programme is a first for Europe.
Bill Davis, Keele, UK

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