Frass on carrot disk
Frass from ambrosia beetles on a carrot disk, with C. lukuohia growing in the middle.

Researchers at the College of Tropical Agriculture and Human Resources (CTAHR) at the University of Hawaiʻi at Mānoa have published the first study to confirm the role of ambrosia beetles in Rapid ʻŌhiʻa Death (ROD).

Xyleborus ferrugineus, a non-native ambrosia beetle, is one culprit in the spread of Ceratocystis lukuohia, a tree-colonizing fungus that leads to widespread ROD in ʻōhiʻa lehua trees in the Puna area of Hawaiʻi Island, according to Kylle Roy, formerly of CTAHR’s Department of Plant and Environmental Sciences.

Roy and other researchers found the beetle frass contained 62 percent C. lukuohia DNA and that 17 percent of the frass had viable fungus spores with the potential to spread to healthy ʻōhiʻa trees. Frass is the sawdust and woody droppings produced by ambrosia beetles and other wood-boring insects when they bore into and colonize trees.

“Other players or species are creating potentially infectious frass as well,” said Roy. “Once we have a better handle on what species we are dealing with, we can develop better management strategies.”

“This study shows the wood dust that ambrosia beetles create, when they attack and burrow inside ROD-killed trees, can contain living C. lukuohia fungal spores and is likely a contributing source of fungal inoculum on Hawaiʻi Island,” adds CTAHR researcher Marc Hughes. “Further research is needed to better understand to what extent boring dust plays in the larger context of ROD-induced mortality on the island.”

Read the full story on CTAHR’s website.