Negative Effects of Scale Insect Herbivory on the Ectomycorrhizae of Juvenile Pinyon Pine

Abstract

An important mycorrhizal mutualism in plants is known to be influenced by herbivory. In contrast to most previous studies that have focused on grass and crop species, here we examine this interaction with trees of known resistance and susceptibility to insect attack under field conditions. To examine the potential interactions between ectomycorrhizae and herbivory, we quantified the levels of ectomycorrhizal colonization of °30—yr—old pinyon pines (Pinus edulis) that were either resistant or susceptible to the sap—feeding scale insect Matsucoccus acalyptus. Resistant trees had lower scale survivorship and retained more of their foliage over a 7—yr period than susceptible trees. Resistant trees also had 28% more ectomycorrhizae than susceptible trees. To examine the cause of these ectomycorrhizal differences we removed scales from susceptible trees and compared their levels of ectomycorrhizal colonization with those of susceptible trees and compared their levels of ectomycorrhizal colonization with those of susceptible and resistant control trees. Following the removal of scales, the levels of ectomycorrhizal colonization of susceptible trees rebounded and did not differ from those of trees resistant to scale attack. These results demonstrate that herbivory by scale insects reduces the ectomycorrhizae of susceptible trees.