The external signs of ambrosia beetles are small piles of white boring dust, or "frass" on the surface of the target plant.  The frass can also look like toothpicks emerging from the entry holes on the trunk of the target tree. Often times you will find what looks like sawdust at the base of a tree infested with ambrosia beetles. The term "ambrosia" refers to the fungus that the insect carries with it into the host plant. Growth of the fungus in the wood produces a black and gray stain surrounding the beetle tunnels.