The tracks of elm bark beetles on the trunk of an elm tree killed by Dutch elm disease. The bark- boring beetle is a vector of the fungus, Ophiostoma ulmi, which is the causative agent of the disease. The sticky conidia of the fungus adhere to the fertilised female beetles & are deposited under the bark, where they germinate. Infection spreads rapidly, but is confined to the water conducting vessels of the tree. The symptoms of the disease are yellowing & browning of foliage followed by wilting, defoliation & finally death.