Invasive Shot Hole Borers Continue to Spread in Southern CA
Since 2010, the polyphagous shot hole borer (PSHB) was thought to be the only exotic shot hole borer impacting southern California. However, in 2015, genetic analysis of the beetle population found that the San Diego population was actually a unique, yet closely related Euwallacea species. Consequently, there are now two known exotic Euwallacea species impacting hardwoods in southern California: the PSHB (Vietnam origin) and the Kuroshio shot hole borer (KSHB; Taiwan origin). Each species has its own unique symbiotic fungal
Willow dieoff from Kuroshio shot hole borer, Tijuana River Valley Regional Park, San Diego Co. Dec. 2015. By Akif Eskalen, UCR
pathogens (Fusarium sp.) that it farms for food in reproductive hosts (support beetle rearing). These fungi grow in tree tissue, clogging the vascular system, and thereby minimizing the tree's ability to transport food and water, ultimately leading to tree stress and sometimes death. PSHB currently has 38 known reproductive host species and KSHB has 14; more may be added as research continues. Reproductive hosts are often riddled with holes from beetle activity, compromising tree structural integrity and health. Hosts include native tree species, common ornamental plants, and agriculturally important species, such as avocado.
Polyphagous shot hole borer infestations have become fairly extensive in Los Angeles and Orange Counties with much smaller distributions in San Bernardino and Riverside Counties. In late 2015, PSHB adults were found for the first time in Ventura County traps near Santa Paula and Ojai. KSHB distribution has been almost exclusively in San Diego County, though some adults were recovered for the first time in 2015 from a trap in eastern Orange County, near a wood yard and in close proximity to a known PSHB infestation. PSHB and KSHB are readily spread to new areas through the movement of infested wood. Drought does not appear to be a contributing factor to beetle success as these borers thrive in riparian and well-watered areas.
There is concern that this beetle/disease complex can spread to other areas of the state where reproductive hosts are present through movement of infested wood. For more information on these invasive shot hole borers, go to http://ucanr.edu/sites/pshb/.
When buying wood to heat your home this winter, remember to buy firewood from local sources, helping to minimize the spread of pests and diseases -
Buy It Where You Burn It. For a list of firewood dealers local to where you live, go to