Identifying the Polyphagous Shot Hole Borer Beetle

This newly discovered beetle is morphologically indistinguishable from the tea shot hole borer, and is believed to vector a new Fusarium sp. leading to Fusarium dieback disease that affects avocado trees. The beetle is a new Euwallacea species — a relative of the tea shot hole borer — and has been identified on over 100 different plant species in California, including avocado, persimmon, peach, olive and citrus trees.

• The beetle, discovered in and around Los Angeles County, is difficult to see. It is smaller than a sesame seed (about 0.1 inch in length).
• The beetle holes penetrate approximately 0.4-1.57 inches into the wood and the entry holes are about 0.033 inches wide.
• Beetles typically leave many exit and entry holes in an infested avocado tree.
• Female beetles are black and about 0.07-0.1 inch long; males are brown and about 0.05 inch long.
• Beetle larvae live in galleries within the tree and feed on the fungus.

The beetle is a vector for Fusarium dieback disease

The beetle and Fusarium fungus have a symbiotic relationship. The beetle burrows into the avocado tree and inoculates the tree with the fungus carried in its mouthparts. The tree eventually exhibits symptoms of branch dieback because the fungus affects the vascular tissues that distribute water and nutrients from the roots to the rest of the tree.

If you suspect you have found this beetle or see symptoms of Fusarium dieback in your avocado groves, contact your local farm advisor, pest control advisor, county Ag Commissioner office, or the CAC office at 949-341-1955. Dr. Akif Eskalen, from the University of California, Riverside, can assist in confirming the existence of the pathogen. He can be reached at 951-827-3499, or email at [email protected].