Walnut twig beetles are native to the southwestern U.S. and parts of Mexico, where their host is the Arizona walnut (Juglans major), but the beetles have increased both their range and the types of host trees. The beetle/fungal duo threatens native stands of walnuts and wingnuts, along with agricultural and timber crops in various parts of the U.S. and  Italy. Infestations can cause significant dieback in trees such as shown here. (Photo by Jackson Audley, Ph.D.)