Mycorrhizal plants mediate interactions between their root‐associated fungal symbionts and insect herbivores. Arbuscular mycorrhizal (AM) associations tend to boost phloem sap sucking insects and host specialist chewing insects but depress host generalist chewing insects. In turn, insect herbivores have only small negative effects on the abundance of AM fungi. Ectomycorrhizal (EM) associations, less studied, have no consistent effect on phloem sap‐sucking or chewing insects, but their insect herbivores have strong negative effects on EM fungal abundance.
Spittlebugs (Hemiptera: Cercopoidea) feed on xylem sap and are disproportionately associated with EM plants, probably because many EM fungi are especially well equipped to access nitrogen (N) from complex soil organic matter. Assimilated N is transported in host plant xylem sap as amino acids, the primary food source for xylem‐feeding insects.
Although EM plants account for only 2% of all vascular plants, about 19% of spittlebugs have EM primary hosts. This compares to 9% of hosts that are rhizobial or actinorhizal N‐fixing plants, alternative modes of root‐associated N acquisition that also attract spittlebugs.
Notable spittlebug EM host plants include Pinus and Abies (Pinaceae), Quercus, Alnus and Betula (Fagales), Salix (Salicaceae), Eucalyptus (Myrtaceae) and the gymnosperm Gnetum (Gnetales).
Some EM plants, including several Pinus species, host spittlebug pests and some play an important role in the ecology of spittlebug vectors of the bacterial plant pathogen Xylella fastidiosa.
The fossil record and dated molecular phylogenies suggest that spittlebugs initially evolved in parallel with EM Pinaceae.