Invasive Shot-Hole Borers
Invasive Shot-Hole Borers
Invasive shot-hole borers may be tiny, but they can damage many different types of trees. They carry several types of fungi that grow in the beetles' tunnels and serve as food for the adults and larvae.
Symptoms are visible clues that a tree is suffering from a pest or disease. “Gumming” is dried sap
on the bark of a tree, a common tree response to attack by insects or pathogens.
When polyphagous shot hole borer females enter or leave their host trees, they leave tiny holes smaller than the tip of a ballpoint pen on the tree’s bark.
This avocado tree is showing wilting and dead branches due to an invasive shot-hole borer attack.
Oozing sap (a sticky liquid substance produced in the tree) and dark patches around borer holes are seen on the bark of some trees.
Some trees really freak out when they are attacked by invasive shot-hole borers! Avocado trees (Persea americana) produce ‘sugar volcanoes’ which are piles of white powder around the beetle holes.
Host trees are trees that invasive shot-hole borers damage. A coast live oak (Quercus agrifolia). This and other oak trees (Q. lobata, Q. engelmannii) are threatened by the invasive shot-hole borers.
Branch of a coast live oak, a native California species threatened by invasive shot-hole borers.
Leaves and fruit of a sycamore (Platanus sp.) Also called ‘plane trees,’ they are often used as landscaping trees and are often found in the wild next to streams. Several sycamore species are attacked and killed by the polyphagous shot hole borer.
Sycamores (Platanus sp.) have very cool multi-colored bark!
Leaves of a boxelder tree (Acer negundo). Unlike most other maples, boxelder trees have leaves made up of 3 to 7 leaflets. Invasive shot-hole borers attack this and other maples, which are often planted as landscape trees.
Seed clusters of the boxelder tree. The seeds are in long strings and come in pairs. Each seed has a little wing attached to it to help it travel farther from the parent tree.
Cross section of a tree infested with invasive shot-hole borers. The branching tunnels made by the beetles weaken the tree’s structure, causing branches to break off.
Invasive shot-hole borer galleries (black holes) and black staining from its Fusarium friend on a willow tree. Willows (Salix spp.) are another host for the beetles and fungi they carry.
Dark staining from the Fusarium fungus can be seen around the beetle holes and in the trunk of this sycamore tree.
The branch of this castor bean plant is showing discoloration because its water-conducting tissue, or xylem , is clogged by the Fusarium fungus .
This sycamore tree (Platanus sp.) is in bad shape because of invasive shot-hole borers. The brown leaves and dead branches are a result of damage to the tree’s water transport tissue, called the "xylem ."
Avocados (Persea americana) provide shade and fruit. Avocado is a very important crop in California, where it is grown on nearly 60,000 acres and the fruit is worth around $435 million every year! Unfortunately, invasive
shot-hole borers pose a serious threat to this crop.
Do you think you've found evidence of invasive shot hole borers? Click the "learn more" button below to read about the borers and to get in touch with the experts.
Tree damage, adult beetle, eggs, beetle galleries, entry hole, avocado dieback, sugar volcanoes, willow tree, infected Sycamore trees, infected castor bean: Akif Eskalen, University of California Riverside. Side view, top view: Javier E. Mercado, Bark Beetle Genera of the U.S., USDA APHIS PPQ, Bugwood.org. Life stages: Michael Lewis, University of California Riverside. Gumming: Erich G. Vallery, Bugwood.org. Weeping tree: Trish Gussler, Flickr.com. Coast Life Oak: Mark Gunn, Flickr.com. Coast Life Oak branch: Tracie Hall, Flickr.com. Sycamore leaves and fruit: Allen Bridgman, South Carolina Department of Natural Resources, Bugwood.org. Sycamore trunk: Ruby T., Flickr.com. Boxelder leaves: Robert Vidéki, Doronicum Kft., Bugwood.org. Boxelder seed clusters: Kent McFarland, Flickr.com.