It is generally not a good thing to see holes in ones' tree, though they do not always signify major problems. Take these holes, for instance. This is a photo of a mature apple tree in my back yard. This tree, which we guess to be between 20 and 25 years old, is hale and hearty (yes, attacked by the usual apple diseases, but the wood is sound). There is no sign of any infestation in the tree, so what are these holes? If you see a series of closely-spaced holes drilled into a tree in a linear fashion it is the sign of a woodpecker, not invasive bugs. Generally your tree will do just fine with this kind of damage, the holes will seal over and the tree with survive. If you want to to avoid this, provide an alternative food source, i.e., suet, for these birds in winter (though some say this will simply attract the birds to your yard!). I think wrapping the tree would be ineffective (woodpecker beaks are very strong, as are their neck muscles) and unattractive. If you see non-linear holes (not like the above) in your trees and: the tree is in decline; there is a exudate from the hole (sappy, gelatinous gunk) and/or: the areas around the hole are rotting, it it time to do more investigation!
Happy gardening!
