NEGATIVE EFFECTS OF SCALE INSECT HERBIVORY ON THE ECTOMYCORRHIZAE OF JUVENILE PINYON PINE

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 c onditions. To examine the potential interactions between ectomycorrhiz ae and herbivory, we quantified the levels of ectomycorrhizal coloniza tion of almost-equal-to 30-yr-old pinyon pines (Pinus edulis) that wer e either resistant or susceptible to the sap-feeding scale insect Mats ucoccus acalyptus. Resistant trees had lower scale survivorship and re tained more of their foliage over a 7-yr period than susceptible trees . Resistant trees also had 28% more ectomycorrhizae than susceptible t rees. To examine the cause of these ectomycorrhizal differences we rem oved scales from susceptible trees and compared their levels of ectomy corrhizal 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 t hose of trees resistant to scale attack. These results demonstrate tha t herbivory by scale insects reduces the ectomycorrhizae of susceptibl e trees.