Elevated anthocyanins protect young Eucalyptus leaves from high irradiance but also indicate foliar nutritional quality to visually attuned psyllids.

1. Foliar colour changes with age and, as a consequence, reflects the internal physiology of leaves. Anthocyanins are 'red' pigments known for their photoprotective role in young leaves and have been suggested to influence the host-finding behaviour of insect herbivores. The existence of colour vision in some species of Eucalyptus-feeding psyllid provides evidence for the possibility of them being able to locate and select leaves based on their age. 2. The preferences of three psyllid species, namely Anoeconeossa bundoorensis, Glycaspis brimblecombei, and Ctenarytaina bipartita, for leaf colours were tested using live leaves of different age, presented without olfactory cues. Changes in foliar pigment concentrations and relationships with amino acid composition in these psyllid's hosts, namely Eucalyptus camaldulensis and Eucalyptus kitsoniana, were studied to consider the adaptive significance of selecting leaves based on their age. 3. The preference for and attraction to young, anthocyanic leaves of two red-sensitive psyllid species ( A. bundoorensis and G. brimblecombei) were demonstrated, whilst the green-yellow-sensitive species ( C. bipartita) was shown to discriminate between young 'yellow' and older 'green' leaves. Age-related variation in leaf colour was positively correlated with greater availability of essential amino acids. 4. This study presents a unique example of herbivore attraction to 'red' leaves and strong evidence for reliance on colour vision in insect orientation at the within-host level. [ABSTRACT FROM AUTHOR]