Beetles then move from twigs to trunks and larger branches of elm trees that are weak, dying or recently killed. Females excavate an egg gallery under the bark, running parallel to the wood grain. After mating, they lay eggs along the gallery. Later the grub-like larvae hatch and tunnel away from the central egg gallery. Typical egg and larval gallery of European elm bark beetle.
Gallery runs up and down, parallel to the the wood grain.
Larvae that overwinter under the bark become mature by midspring, pupate and emerge as adults in May and June. Adults that feed during this period spread the disease to new trees. When an early summer generation is complete, adults emerge in mid- to late summer. New infections are rare during this second period of beetle activity. The xylem vessels of the summer wood are smaller and restrict movement of the fungus.