Tuesday 7 February 2012

The impact of Harlequins on native ladybird fauna

ResearchBlogging.orgHarlequin ladybirds (Harmonia axyridis) are one of the most obvious invasive species in the UK. They are large and voracious and there was much speculation on their potential negative impact on the native ladybird fauna, given that they are regular predators of other ladybirds, especially during the vulnerable larval and pupal stages. An open access paper published today by Helen Roy and collaborators uses a powerful combination of citizen science (in the form of Ladybird online surveys) and systematic surveys to address directly the impact of Harlequins on the distribution and abundance of eight once common and widespread ladybird species in the UK, Belgium and Switzerland. Their statistical analysis on geographic distribution addressed the impact of the arrival of Harlequins on each species for well-sampled km2.
 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.
Figure 1 Effects of Harlequin arrival on the distribution of eight native ladybirds based on predictions for an average 1-km2. Prediction is based on the fixed effects of the models and ignores random variation in occupancy among specific 1-km2. Absent assumes the 1-km2 is not colonized by the Harlequin, and present assumes the 1-km2 was colonized in 2001 (Belgium) or 2004 (Britain) by the Harlequin. Note that our predictions are shown in the measurement scale (probability of occupancy), rather than the modelled scale (logit). (from Roy et al 2012)
  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 

More information
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

Gardiner MM, O'Neal ME, & Landis DA (2011). Intraguild predation and native lady beetle decline. PloS one, 6 (9) PMID: 21931606

Gagnon AÈ, Heimpel GE, & Brodeur J (2011). The ubiquity of intraguild predation among predatory arthropods. PloS one, 6 (11) PMID: 22132211

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