In 2012, avocado growers were presented with the news that a newly discovered invasive beetle, named the polyphagous shot hole borer (Euwallacea fornicatus), could play havoc with production in Californian groves. Native to southeast Asia, the new arrival was a species of ambrosia beetle, a small weevil that bored into the sapwood (xylem) of host trees, creating brood galleries where they cultivated symbiotic “ambrosia” fungi that the beetles and their offspring fed on. Those fungi included a Fusarium species which also acted as a pathogen to the avocado tree, and could lead to branch dieback and, in extreme cases, mortality. Those fears were fortified two years later when a second “Doppelganger” species, the Kuroshio shot hole borer (Euwallacea kuroshio), that looked and behaved exactly the same as the polyphagous shot hole borer, was also found to have established in California. A decade on, those fears have diminished somewhat. Although the two beetles, collectively called invasive shot hole borers (ISHB), remain a serious threat to many tree species in natural and urban environments, it appears that ISHB can be largely controlled in avocado (in California at least) through vigilant cultural care; removing infested branches, followed by chipping and solarization.
With the threat to avocado posed by ISHB allayed, a new project is seeking to prepare growers (and land managers) for the eventuality that a similar but more dangerous non-native ambrosia beetle invades California. The redbay ambrosia beetle (RAB) (Xyleborus glabratus) has not been detected in California but is well-established in the southeastern United States, having been first found in Georgia in 2002. Like ISHB, RAB also carries along a fungal food source, Harringtonia lauricola, and that fungus causes a disease in some host trees. However, laurel wilt, as the disease is called, is much more lethal. Since RAB was first detected, laurel wilt has killed hundreds of millions of redbay (Persea borbonia) trees in the southeastern US and now occurs in 12 states. It continues to spread in the eastern US aided by another susceptible native tree, sassafras (Sassafras albidum), and in 2025, the disease “jumped” some 500 miles to Suffolk County, New York. A similar “jump” to California could spell disaster for the avocado industry.
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