The Colorado State University Plant Disease Clinic can perform these cultures. Beetles that emerge from infected trees and logs often carry spores of the DED fungus on their bodies. As they move to new trees, the beetles first feed in the crotch area of twigs in the upper crown of the tree. The fungus begins to grow and spread within the xylem. 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.