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Ambrosia Beetles in the News

Tuesday, June 27, 2017   (0 Comments)
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Ambrosia Beetles in the NewsConcern about ambrosia beetles continues to grow among nursery producers as new reports surface of their destructiveness.

Various species of ambrosia beetles are well established in the U.S. and are known to be problematic, such as the granulate ambrosia beetle, Xylosandrus crassiusculus, and the black stem borer, X. germanus. Both of these are common throughout the Midwest eastward to the East Coast. Now, Southern California has an ambrosia beetle threat. Two relatively new species were identified in California in 2012, a polyphagous shot hole borer (PSHB), Euwallacea sp., and Kuroshino shot hole borer, Euwallacea sp., Similar to the ambrosia beetles in the eastern half of the U.S., these two pests damage trees by tunneling into stems/trunks/branches and cultivating a fungal symbiont, Fusarium sp.

The PSHB and Kuroshino shot hole borer are similar species but distinct genetically. Both have a relatively broad host range, but one that is different compared with the species on the East Coast and in the Midwest. However, many woody landscape plants are at risk. Another difference, and one that is particularly troubling, is that PSHB and Kuroshino shot hole borer attack healthy trees and are not attracted to ethanol (as is the case with the East Coast and Midwest beetles). A great number of trees from Los Angeles to the Nevada border and south to Mexico are under threat of beetle attack and subsequent Fusarium dieback in the near future.

For those curious about populations of ambrosia beetles, PSHB and Kuroshino shot hole borer are closely related to tea shot hole borer, which has (so far) only been identified in Florida.

There’s a bit more bad news when it comes to ambrosia beetle. A diagnostic lab recently confirmed Hydrangea quercifolia (oak leaf hydrangea) as a host of the granulate ambrosia beetle, X. crassiusculus, in Alabama. This was an unexpected finding, as hydrangea is not a typical host. However, this ambrosia beetle is known to be a generalist – as long as the tree has been weakened.

Brought to you by Lighthouse, an AmericanHort Program. Article by Jill Calabro, PhD.

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