Landscapers and nurserymen may not know but blue spruce is a preferred host for gypsy moth. The following is a short article on the subject.
State gypsy moth programs and some landscapers have observed that gypsy moth seems to prefer blue spruce. This is especially true when populations of gypsy moth drop in an area - gypsy moth still will be concentrated on blue spruce. It is common to see little or no caterpillar feeding on oaks or any egg masses present on the oaks while a blue spruce nearby can be loaded with gypsy moth larvae. When they pupate and emerge the adult females tend to lay eggs on the blue spruce. The gypsy moth larvae are large and in the last instar stages at this time of year. If they are on spruce they would be doing major defoliation at this point. The take home message: If your customers have blue spruce, examine them closely for the presence of gypsy moth populations. There is something about blue spruce that is highly attractive to gypsy moths.
Adapted from the June 12, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers University of Maryland Cooperative Extension