West Coast trees in the US are being attacked by shot hole borers. The beetles are in the genus, Euwallacea that insect biologists suspect* is a multi-species complex rather than a single species. The Tea Shot Hole Borer, Euwallacea fornicatus, is an invasive pest from Asia that invaded Florida early in the 21st century. The beetle has spread but damage appears limited.
In 2010, Euwallacea spp. beetles killed box elder trees in Long Beach and have since been found in avocados where they distribute a tree-killing fungus. The avocado attacking Euwallacea spp. has DNA that differs from the Tea Shot Hole Borers from Sri Lanka and south Asia, but is identical to an avocado attacking Euwallacea spp. pests of avocado in Israel. The invasive species in California may be a different species and separate introduction from the one on the West Coast. The beetle is suspected of being transported in international shipments of ornamental trees.
Ambrosia beetles bore holes in trees but do not feed on the wood. They carry fungi in structures (called mycangia) on the wings and body. The fungus grows in the tunnels created by the beetles The beetles don’t eat the wood. They eat the nutritious fungus. In native areas, the beetles, fungus and trees may reach an accommodation in which healthy trees can tolerate the fungus and are not killed by it. When the beetle and its fungus travel to foreign lands through global trade, the native trees may lack defenses and will be killed by the fungus. In the long run, tree varieties my evolve or be produced that tolerate the fungus. In the short term saving trees and fruit crops means the beetle populations must be managed and their spread stopped or slowed
*UC Riverside, Center for Invasive Species Research. Polyphagous Shot Hole Borer (Euwallacea sp.) and Fusarium Dieback (Fusarium sp.)