While the adult EAB beetle only nibbles on ash foliage, causing little damage, the problem lies with the larvae. Female borers lay their eggs underneath an ash tree’s outer bark. As the larvae grow and mature, they tunnel and feed on the tree’s inner bark, destroying its xylem and phloem tissue. This disrupts the tree’s ability to transport water, mineral nutrients and photosynthetic sugars to all parts of the tree, eventually killing it.
Multiple species of borers exist in addition to EAB. Borers, in general, will primarily attack only unhealthy or stressed host plants. In its native range, EAB works in a similar manner. However, since our native ash trees do not have any inherent defenses against EAB, all species of ash trees in Minnesota, whether healthy or not, are susceptible to destructive attacks.