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Invading alien with an appetite eats its way to insect domination
THE term harlequin was used in old French plays to describe a character who was a messenger of the devil, wandering the earth accompanied by demons.
The harlequin ladybird is aptly named, then, being an alien (if colourful) species which represents bad tidings for many other living things in our gardens and countryside.
Its arrival in the UK, first noted four years ago, is likely to threaten more than 1,000 species, say scientists. It has become a common sight as it has spread across the country – even invading houses in the autumn to hibernate in large numbers over the winter.
The ladybird is originally from Asia but was introduced to continental Europe to control pest insects which were damaging crops. It has since spread to the UK on fruit and flowers and by being blown across the Channel.
A survey launched in 2005 has, with the help of the public, managed to track the harlequin ladybird's progress using more than 30,000 online records. Since its arrival, the ladybird has spread from Essex to Orkney in four years with some areas, including parks, now recording the insect in staggering numbers.
It is a voracious predator, feeding on a wide variety of insects, including the larvae of other ladybirds, caterpillars and even fruit, a much more efficient feeding machine than native species of ladybird. As a result, it poses a major concern for UK wildlife, according to Dr Helen Roy of the Centre for Ecology and Hydrology (CEH).
Evidence from the US, which introduced the harlequin more than 20 years ago, shows severe declines in native species.
"We believe that the negative impacts of the harlequin on Britain will be far reaching and disruptive, with the potential to affect over 1,000 of our native species, many of them very useful ones," says Dr Roy.
"It's a big and voracious predator, it will eat lots of different insects, soft fruit and all kinds of things. Its reproductive capacity is immense and its rate of spread is dramatic and unprecedented." The harlequin reproduces at five times the rate of native species.
It has a variable appearance and is very difficult to tell apart from our 15 species of native ladybirds, although a frequently-sighted version is orange with many black spots, and brown legs rather than the usual black.
It can chomp through more than 12,000 aphids a year. But it is also known to eat species such as lacewing larvae as well as pest insects carrying pathogens, depleting the supplies of the diseases which normally keep such species under control.
"It will try anything it comes across when hungry, and has even been recorded eating the caterpillar of a brimstone butterfly," Dr Roy says.
Scientists from five organisations including Hull University are presenting findings on the harlequin at
the Royal Society Summer Exhibition this week, and
the boffins' warning is that of "one winner, 1,000 losers". Ladybirds do not have many enemies, as they are distasteful and toxic to many predators and let would-be diners know this with their bright colouring. The harlequin ladybird has even fewer predators as it is not a native species.
But the researchers are exploring how the few native enemies that exist, including fungal disease, male-killing bacteria, parasitic wasps and flies could be used to control the harlequin population – or could evolve to tackle the harlequin naturally.
One of the most promising ideas could involve encouraging the transmission of a sexually transmitted mite which makes some ladybirds infertile.
Dr Remy Ware, of the
University of Cambridge, who is working on how the mite could control harlequin populations, says the mite in question is a naturally-occurring UK species which does not affect most British ladybirds because of their breeding cycles.
She says her team is investigating whether the mite could be artificially transferred
to harlequins, where the ladybird's breeding pattern may allow it to be naturally transmitted, causing females to become sterile.
Dr Roy says that if the harlequin is found in the habitat of rare ladybirds such as the five spot, which lives in just a few sites of disturbed river shingle in Wales, it may have to be physically removed to protect the native insect.
But to succeed in any control of the harlequin measures would have to be taken elsewhere as well, which is why the UK Ladybird Group is working with scientists worldwide. Dr Ware says the researchers were not encouraging people to kill harlequins, as it would make no difference to the overall population and they may accidentally kill native species.
"As well as investigating how we can artificially control the population, we're hoping that nature will intervene to help us in finding a way of controlling them."
sheena.hastings@ypn.co.uk
n The scientists from CEH, the University of Cambridge, Anglia Ruskin University, Rothamsted Research and the University of Hull are at the Royal Society Summer Exhibition in London this week.
n To take part in the harlequin and native ladybird species surveys go to www.harlequin-survey.org and www.ladybird-survey.org
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Saturday 26 May 2012
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