The effect of the tree species ratio of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) on polyphagous and monophagous pest species – Lymantria monacha L. and Calliteara pudibunda L. (Lepidoptera: Lymantriidae) as an exampl

Forest monocultures with tree species outside their native range are assumed to be more prone to insect outbreaks than mixed forests. The present study examined this thesis by observing two lepidopteran pests with different dietary spectra. Lymantria monacha L. (Nun moth) is a pest of the Norway spruce [Picea abies (L.) Karst.] that feeds polyphagously on coniferous and deciduous tree species. The second target species, Calliteara pudibunda L. (Pale tussock moth), is a monophagous pest of European beech (Fagus sylvatica L.). We investigated the relative abundances of these two pests in six forest types: pure spruce, pure beech and four mixed stands with different ratios of both tree species. The moths were caught with light traps.The relative abundances of C. pudibunda appeared to be linked to the tree species composition of the investigated forests. The number of individuals and the values of species dominance of C. pudibunda decreased with rising spruce ratio. Beech forests with a small portion of spruce (25%) showed a remarkably strong decrease in the number of C. pudibunda individuals compared to pure beech forests. No significant effects were observed concerning L. monacha and the beech/spruce ratio of the forests, though there was a trend for the dominance of this pest to decrease with rising beech ratio in the forests.