Figure 3. Correlations between P. vulgatissima and natural enemies.

Each data point represent the mean density of the three Heteropteran predators Orthotylus marginalis, Closterotomus fulvomaculatus and Anthocoris nemorum added together, and the leaf beetle Phratora vulgatissima over seven years (1999–2005) in willow plantations (top figure) and natural willow stands (bottom figure). There was a significant negative correlation in the natural habitat (r = −0.46, P = 0.019, n = 20), but not in plantations (r = –0.06, P = 0.40, n = 20).