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The introduction of harlequin ladybirds (Harmonia axyridis) to Europe is driving the decline of native European ladybirds, reports a new study.

The harlequin ladybird – a native of Asia – is good at hunting pests such as aphids, and was introduced to Europe as a biological control in the late 1980s. The recent study examined data collected by volunteers for over 40 years, before the harlequin ladybird was introduced. This data allowed scientists to examine whether there was a correlation between the arrival of the harlequin ladybird and a decline in native ladybird species.

The results showed that the arrival of the harlequin ladybird coincided with the native species' decline. "It is very likely that there are a number of factors driving changes in ladybird populations. Our study focused on just one – the arrival of the non-native species – the harlequin ladybird," explained lead author Dr Helen Roy of the Centre for Ecology and Hydrology. However, the correlation between the arrival of the harlequin ladybird and the decline in the native species was highly significant. "We can conclude that the harlequin ladybird is a strong driver of change in ladybird community composition," said Dr Roy.

Invasive species, such as the harlequin ladybird, are outcompeting native species and resulting in a decrease in biodiversity. "We are concerned that the resilience of the ecosystem may be reduced because of the alteration in community structure of ladybirds (many of which feed on pest insects such as aphids) – that is the service that ladybirds provide in controlling pest insects may be diminished because of the declines in many species," Dr Roy explained.

About the scientist: Dr Helen Roy

What motivated you to become a scientist?

I have a passion for natural history and ecology. I am fascinated by the way in which species interact – there are so many magical twists to what can seem like simple stories within science, and I have a strong desire to unravel some of the mysteries.

Ladybirds are an amazing group of insects – they are icons of our countryside but exhibit some quirky and intriguing behaviours. My imagination was captured by ladybirds in 1976 (I was 6 years old) when the numbers of 7-spot ladybirds were extremely high. I can remember watching the colour develop on a newly emerged adult beetle – changing from yellow to bright red with black spots.

I have had the privilege of working on ladybirds for 18 years – studying their behaviour, distribution and interactions with other species. This year I wrote the Atlas of ladybirds alongside three other ladybird enthusiasts!

What is the best thing about the research you do?

There are so many wonderful aspects to be a scientist (from science communication and collaboration to being in the field alone with ladybirds) – but discovering the unexpected is perhaps the most exciting.