The thorn-limb borer evidently prefers certain trees, in which it breeds year after year, while others nearby will be practically unaffected. The larva is the destructive stage. A roundheaded borer, the larva burrows beneath the bark in the outer layer of wood. The combination of the oviposition slits chewed by the female and the larval tunneling causes the wounded tissues to bleed sap. The twig portion between the slits thickens and the infested section of the branch consequently becomes a gall-like, gnarly swelling.
Infested twigs are very subject to wind breakage.
The fact that this beetle either flies very little, or favors certain trees which it infests year after year, can make this borer very destructive to selected hawthorns. Several factors enter in. TLB injury is higher on the tree and therefore more easily observed. The bleeding and swelling also help in locating infested branches. The TLB life cycle is shorter, affording more opportunity to detect the infestation and control by spraying, pruning, etc.