The results are very clear, but also worrisome: the arrival of Harlequins had a negative impact on the distribution of 5 out of 8 species in Belgium and on 7 out of 8 species in Britain. The effect was large and the affected species have now contracted in range. The effects were striking for the small 2 spot ladybird, Adalia bipunctata, - a tree specialist - , which declined a 30% in Belgium and 44% in Britain in the 5 years following the Harlequin arrival. Although some of these species that were already declining, the presence of the Harlequin intensified the rate of decline.
The systematic surveys of ladybird abundance in the tree habitats favoured by Harlequins supported these results and showed that the numbers of all native ladybirds decreased since their arrival, especially markedly in the UK. The only species relatively immune to their invasion is the 7 spot ladybird, a large species that favours herbaceous vegetation and is less likely to overlap in niche with Harlequins.
Local or regional extintions of some tree specialist species seem like a certainty, and the impact this will have on agricultural systems is hard to predict. The following gallery is a celebration of the diversity of native European ladybirds, with the species used in the study.
Pine ladybird, Exochomus quadripustulatus
Orange Ladybird, Halyzia sedecimguttata
A winter aggregation of 7 spot ladybirds, Coccinella septempunctata
Cream Spotted Ladybird Calvia quatuordecimguttata
10 spot ladybird, Adalia decempunctata
2 spot ladybird, Adalia bipunctata
14 spot ladybird, Propylea quattuordecimpunctata
22 spot ladybird Psyllobora vigintiduopunctata
Roy, H., Adriaens, T., Isaac, N., Kenis, M., Onkelinx, T., Martin, G., Brown, P., Hautier, L., Poland, R., Roy, D., Comont, R., Eschen, R., Frost, R., Zindel, R., Van Vlaenderen, J., Nedvěd, O., Ravn, H., Grégoire, J., de Biseau, J., &; Maes, D. (2012). Invasive alien predator causes rapid declines of native European ladybirds Diversity and Distributions DOI: 10.1111/j.1472-4642.2012.00883.x
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Gagnon AÈ, Heimpel GE, & Brodeur J (2011). The ubiquity of intraguild predation among predatory arthropods. PloS one, 6 (11) PMID: 22132211