Friday, June 5, 2015

Walnut twig beetle, native and invasive in the U. S.

Walnut twig beetle (Pityophthorus juglandis) is believed to be native to the southwest but has spread to the eastern U. S., bringing thousand canker disease (fungus: Geosimithia morbia) with it.  Genetic testing reveals that there are two different geographic lineages but areas where the beetle is invasive, they have hybridized.  The two lineages may be considered as two separate species.

Walnut twig beetle (Pityophthorus juglandis) by Steven Valley, Oregon Department of Agriculture,
Thousand canker disease occurs where the beetle has infested walnut trees.  The fungus grows under the bark of the tree wherever the beetles enter, forming many small cankers which cut off the flow of nutrients throughout the tree.  Diseased tree may die in as little as three years.  The beetles and disease were first found in the eastern U. S. in 2010 and have attacked many walnut trees, causing damage to crops and urban forests.

Thousand canker disease (Geosimithia morbia) by Ned Tisserat, Colorado State University,

Source article: Walnut twig beetle's origin, spread revealed in genetic studies
Walnut twig beetle images: Pityophthorus juglandis
Thousand canker disease images: Geosmithia morbida
Walnut twig beetle BugwoodWiki article: Pityophthorus juglandis