Kieskeurige vlinders in de Vlaamse duinen

During the autumn of 2005, we inspected more than a thousand violets for the presence of caterpillars in the dunes of the Westhoek nature reserve, De Panne (Belgium), in order to investigate the host plant preference of the Queen of Spain Fritillary Issoria lathonia.
The dune violet grows on sunny slopes in open dune grassland with some scrub; we compared a cooler, moister coastal area, and a warmer area further inland. The butterfly’s strong decline in these dunes is due to its habitat becoming overgrown.
The female’s choice was not only guided by the host plant’s appearance, but also by its microclimate. Moreover, the appearance of nearby Viola plants played a part. The later, more mobile, stages of the caterpillars also differed from the female butterfly in their preferences. Management measures differ: extensive grazing can help prevent shrub encroachment, but suitable areas with violets need to be temporarily protected from trampling.