Asian Lady Beetles Use Biological Weapons Against Their European Relatives

May 16, 2013 — Once introduced for biological pest control, Asian lady beetle Harmonia axyridis populations have been increasing uncontrollably in the US and Europe since the turn of the millennium. The species has been proliferating rapidly in Germany; conservationists fear that the Asian lady beetle will out-compete native beetle species. 

Scientists from the University of Giessen and the Max Planck Institute for Chemical Ecology in Jena, Germany, have now found the reason why this animal is so successful. Apart from a strongly antibiotic substance − a compound called harmonine − and antimicrobial peptides, its body fluid, the hemolymph, contains microsporidia. These tiny fungus-like protozoa parasitize body cells and can cause immense harm to their host. The Asian lady beetle is obviously resistant to these parasites in its own body. However, transferred to native species, microsporidia can be lethal. 

The Asian lady beetle − a model organism for studying biological invasions 

Because of its delicate, yet extremely variable, patterning, the lady beetle species Harmonia axyridis is sometimes called Harlequin ladybird. However, this insect has no comical characteristics. At the end of the last century, the species − which is native e.g. in China and Japan and therefore called Asian lady beetle − was successfully used in European greenhouses to keep aphid populations in check: It can devour hundreds of aphids per day, as well as many bug species or insect eggs. Yet today, this "bio killer" has escaped from the greenhouses and is spreading massively, but: A rapid and successful propagation of a neozoon − the biological term for a species which is invading new habitats and ecosystems − is not just an inevitable matter of course. In most cases, such a neozoon species doesn't survive or else its population density remains very low, because original and adapted life forms usually prevail in their ecological niche and win interspecific competitions.

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