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Asian lady beetles use biological weapons

During spring and fall, mass occurrences of the Asian lady beetle can often be observed. photo: supplied

lady bugs_cmyk_opt.jpegScientists have recently figured out how the Asian lady beetle has so rapidly overtaken native beetle populations in Europe and North America.

Researchers from the University of Giessen and the Max Planck Institute for Chemical Ecology in Jena, Germany say the Asian beetle is capable of infecting its competitors with a deadly parasite.

First introduced into greenhouses for biological pest control in aphids, Asian lady beetle Harmonia axyridis populations have been increasing uncontrollably in North America and Europe since the turn of the millennium, according to a release from the Max Planck Institute.

“Apart from a strongly antibiotic substance − a compound called harmonine − and antimicrobial peptides, its body fluid, the hemolymph, contains microsporidia,” the release says. “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.”

Like most ladybug species, the Asian lady beetle reflexively secretes fluid from its hemolymph as soon as it is attacked by potential enemies. Although lady beetles generally compete for their common food source, aphids, some beetles also eat each other.

H. axyridis can feed on native lady beetles without harmful consequences. In contrast, native lady beetles that feed on H. axyridis die.

The harmonine has a strongly antibacterial effect and is only found in the hemolymph of H. axyridis, where it is abundant. Both the proteins and harmonine are of interest in medical research where they offer promising targets for the development of novel antibiotics, potentially even those against malaria.

Swarms of the new arrivals can be found in house crevices in the autumn as the insects search for locations to hibernate. They are considered a nuisance that can also cause allergic reactions in humans.

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