The exotic Asian ladybird that was introduced a few years ago is wiping out our native ladybirds. The reason for this is the subject of discussion among researchers. Recently researchers from Giessen, Münich and Jena suggested that spores from a single-celled parasitic fungus carried by the Asian species act as a biological weapon against the native species. Researchers from Wageningen University state that they are very doubtful about this hypothesis in Science.
The Asiatic ladybird (Harmonia axyridis) is overpowering our native populations, such as the seven-spot ladybird (Coccinella septempunctata). The native ladybirds are under threat and in a confrontation with Asian ladybirds invariably come off worse. Which is logical, according to a group of researchers from the three German institutes, as the Harmonia species carries a type of parasitic fungus against which it is itself immune, but against which the native species have no resistance. According to their reasoning this pathogen is decimating the native population.
‘Extremely unlikely’, say Peter de Jong, Joop van Lenteren and Lidwien Raak-van den Berg from Wageningen University’s Laboratory of Entomology in Science (20 September 2013). According to this hypothesis the parasitic fungus would have to be transmitted from Harmonia to the native species. For this to happen, the native species would have to eat the eggs, larvae or even the adults of Harmonia. And this is exactly what makes this hypothesis so unlikely: the Asian ladybird is more likely to be the attacker than the prey and is often so threatening that even their eggs deter the native species. According to the Wageningen researchers: ‘They don’t even need the biological weapon of the parasitic fungus, let alone it being the deciding factor’. In short, they say in their article, there is no evidence that the global success story of the Asian ladybird is due to the transfer of a single-celled pathogen.