Yesterday, while walking to the store. Kelly and I noticed a ornamental plum tree with sap coming out all over. The sap is the tree’s defense against bark beetles. The idea is the tree is ‘pitching out’ the beetle – forcing it out in the sap stream.
This tube represents success for the tree. If a beetle were still in the hole, the sap would be stained with frass. You can see how clean the sap has become. This tree probably had a 100 or so of these pitch tubes. We did not examine all pitch tubes to see what the success rate of the ‘pitch out’ is.
This tree is originally from Asia and is planted as an ornamental. A good guess (at least in my mind) as to the identity of the insect is Scolytus rugulosus. This is a Eurasian beetle. There is a growing body of evidence that the presence of non-native species can help other non-natives species establish.