Red gall pigmentation: cytokinin stimulation is not everything

Recently, the nature of gall pigmentation phenomenon has gained interest, with different, and often contradicting, explanations and hypotheses. A recent, welcome contribution by Connor et al. (Arthropod-Plant Interact 6:489-495, 2012) suggested that gall pigmentation is a mere fabricational noise of the gall development, caused by the production of anthocyanin due to the accumulation of cytokinins and sugars. We propose that this perspective, although probably true in some systems, is an oversimplification of a more complex situation. We argue that since multiple pigments are likely to be involved in gall coloration, and since the link between cytokinins and pigmentation is not obligatory, this is an unlikely general explanation of gall pigmentation. The galling habit has evolved independently among numerous insect lineages and habitats, and therefore, the role of gall pigmentation may vary. It is the time to test the different hypotheses in the field.