The research, published in the journal Insect Conservation and Diversity, involved taking recordings at four sites across East Anglia, nine times a year over an 11-year period from 2006-2016.
Led by Dr Peter Brown of Anglia Ruskin University, who worked alongside Dr Helen Roy of the Centre for Ecology and Hydrology, the research found that the proportion of native ladybirds recorded at the sites (two lime tree sites, one pine tree site and one nettle site) declined from 99.8% in 2006 to 30.7% in 2016.
(Image removed)Only one solitary harlequin ladybird (Harmonia axyridis) was recorded as part of this study in 2006. However, towards the end of the study period, harlequins (pictured top/ credit Nick Greatorex-Davies) accounted for up to 70% of all ladybirds. Harlequins are known to feed on native 2-spot ladybirds (Adalia bipunctata) (pictured right/ credit Mike Majerus) and this predation may be an important driver of the changes observed.
The harlequin was introduced across continental Europe to limit the population of pest insects feeding on a range of glasshouse and field crops. It was first recorded in England in 2004 and is now commonly found across most of England and Wales, spreading at a rate of approximately 60 miles per year in the early stages of its introduction.
Dr Brown, Senior Lecturer in Zoology at Anglia Ruskin University, said: “Our study shows just how numerous harlequin ladybirds have become, and there is no indication that this will change in the short to medium term.
“Ladybirds are sensitive to factors such as food availability and weather conditions, which means that their numbers vary substantially from one year to the next. Therefore long-term monitoring, like our 11-year study, is essential for providing a reliable picture of the changes taking place.
“The 2-spot used to be one of our most abundant ladybird species but is now quite tricky to find. The study shows clear changes in the ladybird community as a result of the harlequin’s dominance.”