FOR DAVID GREEN STORY Harlequin ladybirds, Thorpe Road, Norwich 25-09-07 Photo : Chris Durdin EADT 19/10/07 ES 19/10/07

NATIVE British ladybirds are suffering rapid declines because of the arrival of invasive harlequin ladybirds, research shows

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The Centre for Ecology and Hydrology (CEH) led a study which revealed that seven out of eight UK ladybirds had declined over five years following the arrival of the harlequin in 2004. The two-spot ladybird declined by almost half (44%).

Researchers said the two-spot was now hard to find in some areas where it used to be common.

The research, which is published in the Diversity and Distributions journal, used thousands of records from “citizen science” projects dating back to 1971 to help provide proof of the link between the arrival of the harlequin and declines in other species.

Not only do harlequins out-compete with other ladybirds for prey and habitat, they are also known to eat them, the researchers said.

The research, which stretched across five countries, revealed decreases in numbers of ladybirds have been mirrored in Switzerland and in Belgium, where five out of eight native species saw substantial declines.

In the UK, of the eight species examined, only the seven-spot ladybird, a large insect which is not in as much direct competition for habitat with the harlequin as other species, had not experienced falling numbers.

The CEH’s Dr Helen Roy, who led the survey, said the study provided “strong evidence” of a link between the arrival of the harlequin ladybird and declines in other species of ladybird.

“It’s a very real decline, which should be put amongst a whole other set of factors putting ladybirds in a more fragile situation,” she said.

Other factors potentially affecting ladybird populations include intensification of agriculture and climate change.

She said the two-spot, which closely shares the habitat of the harlequin and so is in direct competition with it, had seen large population falls.

“It’s at such low numbers that it’s difficult to detect in some localities. Where it would have been common, now it’s at such low numbers people just aren’t seeing it,” she said.

The harlequin, a slightly bigger species, spread to the UK after being imported from East Asia to Europe for commercial pest control of crops.

Co-author Dr Peter Brown, of Anglia Ruskin University, said: “This is a very rapid change, the harlequin has swept up Britain, it’s all over England and is now common as far north as north Yorkshire.”

Dr Brown said the harlequin had also been introduced in North and South America, and was doing well on both continents, making the issue a global one.

It feeds off aphids in the same way as native species, but having just one type of ladybird doing the work of a number of species is seen as making the ecosystem weaker.

“If anything then happened to the harlequin, even if you’re not bothered about the other species, you’ve lost your aphid control,” Dr Brown said.