Bright autumn colouration in trees - a warning signal to insects?

Most deciduous trees change colour in autumn. However, both within and between species, there is considerable variation both in the timing and magnitude of autumn colour change. Hamilton and Brown recently proposed a hypothesis to explain this phenomenon.

Their idea was that the bright autumn colouration in trees is a warning signal to insects about investment in chemical defence. In the forthcoming issue of Ecology Letters, Hagen, Jakobsen and Folstad present the first empirical test of this autumn signalling hypothesis.

They show that in mountain birch, increasing degree of autumn colouration in September is associated with a reduction in leaf damage from insects the following season, indicating that the most autumn coloured trees might have been less exposed to egg-laying insects.

This result is consistent with the idea that bright autumn colouration is a warning signal directed towards insects in search of favourable hosts for their progeny.

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