Invasive harlequin ladybirds are feeding on their native British cousins, DNA analysis has shown.
Research analysing the contents of the guts of harlequin larvae across Europe revealed the species, which mainly eats aphids, were also preying on other insects including 10-spot and 2-spot ladybirds.
The harlequin, a larger and more voracious species than native British ladybirds, spread to the UK after being imported from East Asia to Europe for commercial pest control of crops.
Research has previously shown that seven out of eight UK ladybird species studied had declined over five years following the arrival of the harlequin in 2004. The harlequin is now the second most commonly found ladybird species in the UK.
Experts are concerned the invasive species is responsible for the declines of other ladybirds by out-competing them for food and habitat, and by preying on them.
The new study, led by Dr Peter Brown and Dr Alison Thomas of Anglia Ruskin University, is the first to use molecular techniques to probe for the presence of the DNA of several different insects in the guts of harlequin larvae.
A total of 177 larvae were collected from the wild in England, France, Germany, Slovakia and the Czech Republic, and then tested for the DNA of four insects.
DNA of 10-spot ladybirds were found in almost one in 10 (9.6%) of the larvae tested, and 2-spot ladybirds were found in 2.8% of the larvae collected across Europe, with higher rates of detection of both ladybirds in the English samples.
Mar malade hoverfly DNA was also found in 2.8% of all the larvae tested, while the green lacewing was tested for but not found, the research published in the journal Entomological Science showed.
Dr Brown, senior lecturer in zoology at Anglia Ruskin, said: "This study shows that harlequin ladybirds in the wild commonly prey on a number of insects, not just aphids.
"The results offer further evidence that the harlequin is a generalist predator which is having a damaging effect on native species across Europe.
"Ladybird and other aphid-feeding insects are a very important part of ecosystems, acting as natural pest controllers.
"There are 47 ladybird species in the UK and it is vital this diversity is maintained."