Herbivory meets fungivory: insect herbivores feed on plant pathogenic fungi for their own benefit

Plants are regularly colonized by fungi and bacteria, but plant-inhabiting microbes are rarely
considered in studies on plant-herbivore interactions. Here we show that young gypsy moth
(Lymantria dispar) caterpillars prefer to feed on black poplar (Populus nigra) foliage infected
by the rust fungus Melampsora larici-populina instead of uninfected control foliage, and
selectively consume fungal spores. This consumption, also observed in a related lepidopteran
species, is stimulated by the sugar alcohol mannitol, found in much higher concentration in
fungal tissue and infected leaves than uninfected plant foliage. Gypsy moth larvae developed
more rapidly on rust-infected leaves, which cannot be attributed to mannitol but rather to greater
levels of total nitrogen, essential amino acids and B vitamins in fungal tissue and fungus-infected
leaves. Herbivore consumption of fungi and other microbes may be much more
widespread than commonly believed with important consequences for the...