Native to Asia, the harlequin ladybird (Harmonia axyridis) has been introduced to many countries as a pest control agent, but is now spreading rapidly and has itself become a pest species.
Introduced to North America in 1988, the harlequin is now the most widespread ladybird on the continent, and the species has also invaded much of northwest Europe. It was first spotted in Belgium in 2001, and arrived in the UK and Switzerland in 2004.
Since the harlequin’s arrival, scientists have warned about its potentially harmful impacts on native ladybird species. However, new research published in the journal Diversity and Distributions has now measured the scale of these impacts and demonstrated a strong link between the spread of the harlequin and rapid declines in native ladybirds.
Led by the Centre for Ecology and Hydrology in the UK, the study was made possible by thousands of records submitted as part of “citizen science” projects that record ladybird observations across Britain, Belgium and Switzerland.
Using this data, the researchers found that in the five years following the harlequin ladybird’s arrival in the UK, seven out of eight native ladybird species declined. Similar declines were also found in Belgium and Switzerland.
Particularly badly affected was the two-spot ladybird (Adalia bipunctata), which is estimated to have declined by 44% in the UK and 30% in Belgium. It is now difficult to spot in some areas where it was once common.
Like many other native ladybirds, the two-spot ladybird is smaller than the harlequin and likely to be outcompeted for food and habitat. The harlequin is also likely to prey on the eggs and larvae of native ladybird species. In addition, the harlequin ladybird may potentially be more toxic than native species, giving it better protection against predators.
Speaking about the results, Helen Roy of the Centre for Ecology and Hydrology said, “It’s a very real decline, which should be put amongst a whole other set of factors putting ladybirds in a more fragile situation.”
Such factors may include the intensification of agriculture and climate change.
The only UK species apparently unaffected by the harlequin’s arrival was the seven-spot ladybird (Coccinella septempunctata), which is similar in size to the harlequin and not in such direct competition for habitat as other native species.
The researchers have warned of potentially serious consequences if the harlequin ladybird continues to spread. Ladybirds play an essential role in ecosystems, keeping pests such as aphids in check. Although the harlequin ladybird also feeds on aphids, having just one species playing this role could make the overall ecosystem weaker.
Tim Adriaens of the Research Institute for Nature and Forest (INBO) in Belgium, said, “At the continental scale, the arrival of the harlequin could impact on the resilience of ecosystems and severely diminish the vital services that ladybirds deliver.”
Read more on this story at BBC News – Ladybird decline driven by ‘invading’ harlequin and at The Telegraph – Harlequin ladybirds threaten British species.
Liz Shaw, ARKive Species Text Author