The walnut twig beetle, Pityophthorus juglandis, is the vector of
Thousand Canker Disease (TCD), a fungus that causes small cankers, but many of these cankers together kill the tree.
The beetle is native to Arizona, New Mexico, and northern Mexico, where it attacks Arizona walnut.
Since the 1990s, black walnut, a tree native to the eastern U.S. but planted widely in the west as an ornamental has been under attack.
In 2004, widespread mortality in the Front Range of Colorado was linked to the presence of the beetle and the fungus it carries, Geosmithia morbida.
TCD is an example of a native pest that expanded its geographic range and discovered new host species with no coevolved resistance.
For more, view Walnut Twig Beetle and Thousand Cankers Disease of Black Walnut.