If your tree has rows of holes in its trunk, it is probably caused by….

Sapsuckers (woodpecker’s relatives). They are not generally harmful nor do they suggest the presence of any harmful insects. The birds drill their holes, then return to feed on the sap days and weeks later. If they seem to be doing damage, consider a sticky repellent or hit the holes lightly with an aerosol pruning sealant to prevent pests from entering.