CLCA’s Environmental Research Funding Program recently awarded a $14,000 grant to a Department of Plant Pathology team at UC Riverside for a research project on “Assessment of Biological Control Agents to Control Fusarium Dieback/Polyphagous Shot Hole Borer on Wildland Landscape Trees in California.”
Invasive Beetles and Symbiotic Fungal Pathogen Deadly Combination
The Polyphagous Shot Hole Borer (PSHB) is an invasive species of ambrosia beetles that was recently discovered in southern California. PSHB is thought to have originated from Southeast Asia, and its infestation sites have so far been found in Los Angeles, Orange, Riverside, San Bernardino, and San Diego counties.
Like other ambrosia beetles, the PSHB bores into the xylem layer of host plants and creates a network of galleries. The beetles inoculate the walls of the galleries with symbiotic fungi to cultivate them as their sole source of food. Although this fungus is symbiotic to the beetle, it is pathogenic to the host plant. After inoculation into the xylem, the symbiotic fungal pathogen Fusarium euwallaceae grows into the galleries to feed the beetles. It also grows through the xylem vessels away from the galleries to spread towards the rest of the plant. The mycelial mass of these fungi within the xylem vessels eventually obstructs the vessels, causing dieback symptoms and eventual death in the host trees due to restricted water transport. Unfortunately, while other ambrosia beetles mostly colonize dead or dying trees, PSHB beetles prefer to colonize healthy host trees.
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