4 December 2013
Last updated at 13:26
Harlequin ladybirds escape parasites which attack native species, scientists have found.
Harlequin ladybirds settled in the UK from Asia in 2004 and rapidly spread across the country.
The decline of several native ladybird species has been attributed to the arrival of these invasive insects.
Experts studying the invasion found that the harlequins were significantly less susceptible to parasites which prey on native ladybirds.
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The results are published in the journal Insect Conservation and Diversity.
Although their bright warning colours serve to protect ladybirds from larger predators, they do come under attack from tiny parasites.
One of the most common parasites of native ladybirds is the wasp Dinocampus coccinellae which lays its eggs inside the beetle when they are pupae.
The wasp grub develops by stealing nutrients from its ladybird host until ultimately, the wasp emerges and the ladybird dies.
To understand whether native parasites had cosmopolitan tastes, researchers monitored the natural ‘enemies’ of both native seven-spot ladybirds (Coccinella septempunctata) and harlequin beetles (Harmonia axyridis) over five years.
The study revealed that harlequins were targeted by parasitic flies and wasps, but in much smaller numbers than the native ladybirds.
Parasitised seven-spot ladybirds twitch and protect the developing wasp underneath
“It’s really exciting to find that native parasitoid species are attacking the harlequin, but they’re only doing so in really small numbers – the native seven-spotted ladybird is almost 11 times more likely to be eaten than the harlequin,” said Richard Comont who carried out the research as a PhD student at the Centre for Ecology and Hydrology (CEH).
“That really shows in part why the harlequin is increasing so quickly – there’s nothing holding it back.”
Scientists suggest the native parasites – which evolved alongside seven-spot ladybirds and their native relatives – are not well adapted to attack the invaders
The CEH are conducting ongoing studies into the biology of harlequin ladybirds to understand and potentially mitigate their impact on our native wildlife.
“We need people to keep sending in records to the UK Ladybird Survey and we would be delighted to hear about any sightings of parasitised ladybirds,” said co-author Dr Helen Roy.
She said that additional observations by citizen scientists will help to “unravel the story of this alien invader”.
Article source: http://www.bbc.co.uk/nature/25216538