Searching for MALB’s weak spot
By Marg Land
September 11, 2008 — Ecologists
have discovered that – as well as being larger, hungrier and more
aggressive than most native lady beetles – the invasive alien harlequin
lady beetle is also more resistant to fungal disease and a parasitic
wasp, two common natural enemies of native lady beetles.
September 11, 2008 — Ecologists have discovered that – as well as being larger, hungrier and more aggressive than most native lady beetles – the invasive alien harlequin lady beetle is also more resistant to fungal disease and a parasitic wasp, two common natural enemies of native lady beetles.
Speaking at the British Ecological Society’s Annual Meeting at Imperial College, London, UK, Dr. Helen Roy from the Centre for Ecology & Hydrology explained how this resistance to parasites is aiding the harlequin’s spread in the UK and how the results are helping researchers home in on its weak spot.
Dr. Roy compared the behaviour and mortality of both the harlequin and native British lady beetles after infection with the fungal disease Beauveria bassiana. She found that native species succumbed very readily to the disease, whereas most of the harlequins survived. Interestingly, however, the number of eggs the infected harlequins produced was dramatically reduced.
“The harlequin has been a successful invader worldwide,” said Dr. Roy. “This could partly be down to its ability to escape the effects of resident natural enemies, such as this fungal disease, which have a major impact on native (lady beetles).”
“It is fascinating that even though the fungus killed only a few harlequin (lady beetles), the exposed females produced far fewer eggs. We often use death as our only measure of the impact of disease on animals but this study shows that it’s important to look for subtle interactions.”
“Unfortunately, this fungus is not a viable control method for the harlequin because native (lady beetles) are highly susceptible to the disease, so we need to keep looking for other ways to control it. One possibility is semiochemicals – the chemical cues these (lady beetles) use for communication. Scientists are just beginning to understand how semiochemicals vary between different species of ladybird. With time it might be possible to manipulate semiochemicals as a control method, perhaps by using the chemicals to lure harlequin (lady beetles) into traps.”
The harlequin lady beetle, Harmonia axyridis, arrived in England in 2004 and was first recorded in Scotland and Northern Ireland in December 2007. It is the most invasive lady beetle on Earth and is a major threat to British lady beetles because – compared to native species – the harlequin is large, aggressive and has a huge appetite. Harlequins also bite humans and infest vineyards where the defensive chemicals (reflex blood) it produces taint the wine.
In a second paper to the BES Annual Meeting, Dr. Roy talked about the UK Harlequin Ladybird (lady beetle) Survey and the vital part the public has played in spotting the invader.
“The public has played a crucial role in tracking this alien (lady beetle) and has enabled us to build up a detailed picture of where this species is and what it is doing. We can use this information to help answer many questions and we hope that we can learn lessons from this survey that will be useful for understanding other wildlife invasions.”