Invasive harlequin ladybirds are causing rapid declines in native British species of the insect, research revealed, yesterday.
A study led by the Centre for Ecology and Hydrology (CEH) showed that seven out of eight UK ladybirds had declined over five years following the arrival of the harlequin in 2004, with the two-spot seeing numbers fall by almost half (44 per cent).
The researchers said the two-spot was now hard to find in some areas where it had once been common.
The study, published in the journal Diversity and Distributions, used thousands of re-cords from “citizen science” projects dating back to 1971 to help provide “strong evidence” of the link between the arrival of the harlequin and declines in other species.
Harlequins out-compete with other ladybirds for prey and habitat, and even eat their native cousins, the researchers said.
The research, which stretched across five countries, showed falls in numbers of ladybirds have been mirrored in Switzerland and in Belgium, where five out of eight native species had seen substantial declines since the harlequin’s arrival.
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.
Other factors potentially affecting ladybird populations includeintensification 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 species which is slightly bigger and better protected from predation by other ladybirds than some of the UK’s native species, spread to the UK after being imported from East Asia to Europe for commercial pest control of crops.
Co-author 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. “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 warned.