From grey squirrels to Japanese knotweed (pictured), non-native species can cause pandemonium if they become invasive. Expert Dr Dick Shaw from CABI, which specialises in solving problems in agriculture and the environment, explains how biological control can help.
What is biological control?
It is the use of natural enemies to control a pest species. There are various types. One is called “inundative” – using natural enemies that are normally native and mass producing them.
What we’re doing mostly is “classical” – you go back to the area of origin of the pest and you use the natural enemies [from] there. You test them for specificity to make sure they are safe and then you release them, often just once, and then the aim is you have control for ever.
Can we tell which organisms might become invasive?
It is very difficult to predict. One thing you have to remember is that almost all – 99% – of species are benign. There’s a thing called the tens rule: 10% of organisms are able to establish beyond the cosseted environment of the garden and only 10% of those go on to become invasive.
Could biological control agent get out of control?
What people forget is these organisms evolved over millennia to become specialist. It reaches the point where it becomes so linked to its host it can’t feed on anything else.
Are there any big successes?
Rubber vine is an invasive plant species from Madagascar that invaded 40,000 sq km of Australian habitat – we found a rust fungus from Madagascar to use against the plant and now it’s completely reversed the situation. In Britain we had a terrible problem with spruce bark beetle; a predatory beetle was introduced to control it and was incredibly successful.
Weren’t cane toads a bit of a failure in Australia?
It’s one everyone remembers because of the Panorama documentary, but in reality the cane toads were absolute lunacy. It was an organism, a vertebrate predator, that would feed on anything you put in front of it, so it was always going to cause a problem. The bizarre thing was they brought that in for sugar cane beetle control and one of them is nocturnal and the other one is day-living.
What sort of plants are causing a problem in the UK?
Knotweed and Himalayan balsam are two.
You’ve recently released a rust fungus from the Himalayas to control the balsam. What’s the outlook?
Rust fungi tend to be incredibly specific. We are expecting that to spread rapidly, being an airborne spore, and hopefully that will reduce Himalayan balsam on a national scale.
What’s being trialled to control Japanese knotweed?
[An insect] called Aphalara itadori. It’s their offspring that really do the job – they suck the sap out and the plant puts a lot of investment into producing more and more sap. We’ve been doing limited releases at a few sites, isolated away from other knotweed and away from rivers. The regulator will make a decision on how we can proceed. The best-case scenario is we can release it wherever we want on a massive scale. Worst-case scenario is we stick with the sites we’ve got and keep plodding on until we’ve got some more data.
