A couple of months ago I received an E-mail asking about gum spots (those little black flecks) in Black Cherry. I received some information (yet once again!) from my diligent County Forester. I also spoke with an experienced log buyer in Pennsylvania who ships unbelievable cherry all over the world. However, even after this research, I still don't feel like I have a total handle on this. Here's what I found out plus a source for more in-depth information.
Several types of infection and injury can cause gum spots. It is the Cherry tree's attempt to "pitch out", or flush, an affected area (usually the insectís entrance holes) that manufactures gum. When first produced, the gum is clear but it darkens with age. There are two bark beetles that usually cause only minor gum damage: the reddish brown (2.8 - 4.5 mm long) Birch Bark Beetle (Dryocoetes betulae) and the light brown to black (1.5 - 2.2 mm long) Peach Bark Beetle (Phloeotribus liminaris). They generally attack weakened or dying trees and as weakened trees can't produce as much pitch, the damage is usually minor. It is the Leaf Miner Fly (Agromyza pruni), which causes most gum, especially in the Allegheny Plateau. These flies are both light and dark colored and are very small. They are covered with sparse bristles to dense hairs and it is the larvae that "mine" the cambium. My sources don't tell me any controls for the Leaf Miner Fly, but apparently, significant beetle outbreaks can occur when there is a lot of logging slash around. The beetle population beefs up to the point that they can "mass attack" even vigorous trees.
For more information you might try to locate A.F. Hough's publication: "Gum Spots and Pith Fleck in Black Cherry" -- 40 pages with illustrations and published in 1962.