Mite domatia are small structures on the underside of plant leaves that house predacious or fungivorous mites, thereby mediating a plant-mite defence mutualism. It has been suggested that plants benefit more from domatia-dwelling mites when they offer them supplementary food in the form of extrafloral nectar secreted from leaves.
Weber et al. tested this hypothesis by experimentally adding nectar to the leaves of two species of wild grape. They find that foliar nectar can enhance plant-mite mutualisms by increasing the number of mites found inhabiting domatia, which in turn decreased powdery mildew load on the leaf surface. The authors pair their experiments with a survey of the distribution of domatia and extrafloral nectar across the plant tree of life, and show that these two interesting mutualistic traits frequently occur in the same clades.
Marjorie G. Weber, Laura D. Porturas, Scott A. Taylor, 2016, 'Foliar nectar enhances plant–mite mutualisms: the effect of leaf sugar on the control of powdery mildew by domatia-inhabiting mites', Annals of Botany, vol. 118, no. 3, pp. 459-466 http://dx.doi.org/10.1093/aob/mcw118