Invasive Shot Hole Borers (ISHB) (Part II)

Invasive Shot Hole Borers (ISHB) (Part II)

When the beetles bore into a tree, they create a series of tunnels where they farm the fungus and produce young. This series of tunnels is referred to as a gallery. Their winding galleries can reach to a depth of around 3 inches (8 cm) into the tree's wood. The dark stains in the wood is caused by the fungus (Fusarium euwallaceae), which not only causes the beetle's galleries to be stained black, but also moves into the tree's xylem, clogging it. The clogged xylem will prevent the tree from distributing water and nutrients and leads to branch dieback and the eventual death of the tree.

The Fusarium can also cause a sugary exudate (also called a sugar volcano) and gumming.  While inspecting trees you may also see the beetle entry & exit holes (about 0.85 mm or the size of pen head in diameter) and sometimes you can see the abdomen of a female beetle sticking out of the hole.

Fusarium in the gallery and branch dieback in oak.

Beetles and Galleries in the wood.

An infected Sycamore tree that was removed due to potential fire hazard and property destruction in Montecito.

Invasive Shot Hole Borers (ISHB) (Part I)

Invasive Shot Hole Borers (ISHB) (Part I)

There are two types of Invasive Shot Hole Borers that we are concerned about in Santa Barbara County; the Polyphagous Shot Hole Borer and the Kuroshio Shot Hole Borer. The two beetles look the same, but are genetically different and can be identified using DNA analysis. Both shot hole borers are a group of ambrosia beetles that make tiny entry holes in trees.They are ambrosia beetles because they carry a symbiotic fungus with them. The fungus (Fusarium spp.) is carried along by female in special organs in her mouth parts and is used to infest the host plant.  The beetles farm the fungus and both adult beetles and larvae feed on fungus. A mated female will find a suitable host and bore into it to create galleries (a series of tunnels) to farm the fungus and lay her eggs.  These shot hole borers infest healthy trees, but the fungus causes the tree to die slowly by clogging its vascular system and preventing the movement of water and nutrients.  Once the tree can no longer sustain fungal growth, the beetles will fly to a new host.  They spend a majority of their lives within the galleries inside the tree (this makes it very difficult to control the beetles). 

The female (a) is darker and slightly larger than the male (b).