In spring, aphid larvae emerge from eggs laid on host plants and head for the leaves to feed. But, for at least one aphid species (Dysaphis plantaginea), those whose parents laid eggs on apple tree (Malus pumila) hosts with red leaves in the autumn do less well than those laid on trees with yellow or green leaves. Marco Archetti of the University of Oxford, UK, says that this supports the theory that red leaves serve as an 'honest' signal to insects warning against such factors as robust chemical defences.
Domesticated apple trees were selected for nice fruit, not insect resistance, and as such should not advertise defences they have not retained. Accordingly, Archetti finds that domesticated apples rarely have red leaves in autumn. There might even be a direct trade-off; red-leaved trees make smaller, less palatable apples.