A field study with geometrid moths to test the coevolution hypothesis of red autumn colours in deciduous trees

Red autumn colouration of trees is the result of newly synthesized anthocyanin pigments in senescing autumn leaves. As anthocyanin accumulation is costly and the trait is not present in all species, anthocyanins must have an adaptive significance in autumn leaves. According to the coevolution hypothesis of autumn colours, red autumn leaves warn herbivorous insects – especially aphids that migrate to reproduce in trees in the autumn – that the tree will not be a suitable host for their offspring in spring due to a high level of chemical defence or lack of nutrients. The signalling allows trees to avoid herbivores and herbivores to choose better host trees. In this study the coevolution hypothesis was tested with four deciduous tree species that have red autumn leaf colouration – European aspen ( P opulus tremula L.) ( S alicaceae), rowan ( S orbus aucuparia L.) ( R osaceae), mountain birch [ B etula pubescens ssp. czerepanovii (NI Orlova) Hämet‐Ahti], and dwarf birch ( B etula nana L.) ( B etulaceae), and with two generalist herbivores, the autumnal moth [ E pirrita autumnata ( B orkhausen)] and the winter moth [ O perophtera brumata (L.)] (both L epidoptera: G eometridae). Anthocyanin concentrations of autumn leaves were determined from leaf samples and the growth performance parameters of the moth larvae on the study trees were measured in the spring. Trees with higher anthocyanin concentration in the autumn were predicted to be low‐quality food for the herbivores. Our results clearly showed that anthocyanin concentration was not correlated with the growth performance of the moths in any of the studied tree species. Thus, our study does not support the coevolution hypothesis of autumn colours.