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Spread of Rapid ʻŌhiʻa Death may be linked to beetles

  • 4 min to read
Rapid ʻŌhiʻa Death

Samples of different strains of ʻŌhiʻa showcased at the seed banking workshop.

A recent UH study found that the infectious spread of Rapid ʻŌhiʻa Death (ROD) could be due to natural vectors along with human activity. The study, conducted by researchers at the University of Hawaiʻi at Mānoa’s  College of Tropical Agriculture and Human Resources (CTAHR), found that invasive ambrosia beetles may be linked to the spread of the disease through Hawaiʻi’s forests.

“It’s probably one of the bigger issues happening across the landscape now,” she said. “These forests are the foundations of our islands, they are what keeps us here with the water supply and everything. And so without these forests it would be very devastating.”

ROD is a fungal disease that was first discovered on Hawaiʻi island in 2014, and has since spread throughout the island. According to ROD statewide outreach coordinator, Ambyr Mokiao-Lee, this is a pressing issue for the state.

ʻŌhiʻa plays an important role in Hawaiʻi’s ecology, providing food and shelter for native birds, insects, and other species, and is even among the first plants to grow on lava flows which make way for the soil development so vital for life on the islands, according to the CTAHR website.

Besides the tree’s instrumental role in the physical environment, ʻŌhiʻa have cultural significance as well.

“ʻŌhiʻa are woven deeply into Hawaiian culture through symbology in moʻolelo (stories), mele (songs) and ʻoli (chants). ʻŌhiʻa serve as the sacred kinolau (physical manifestations) of multiple Hawaiian deities,” and are used in many native Hawaiian cultural practices, according to the CTAHR website.

The discovery of ROD in 2014 and its ensuing rapid spread has come as quite a blow to many people throughout the islands. This has also led to many efforts to keep the disease at bay and continued research into the cause of the spread and any possible cures.

Prior to the recent study on ambrosia beetles, the means by which ROD has been spreading was shrouded uncertainty. There was no previous research conducted to prove any natural vectors that may be at fault in the spread of the disease. Human activity was the only agent previously known for certain to assist in the pervasive spread. Because of this, residents are urged to take any necessary precautions when entering and exiting the forest to prevent further spread of ROD and other diseases.

“[It is] important for people to do their own jobs of sanitizing and making sure that they can prevent the spread because that is, at this point, one of the only things we can do,” Mokiao-Lee said. “We as humans can change our behaviors to make sure we’re not spreading the disease. But unfortunately when it comes to the beetles that’s just mother nature and there’s unfortunately nothing we can do about that [right now].”

What do beetles have to do with an infectious tree disease? It all comes down to a sawdust-like substance called frass. In the case of ROD, frass is the fine wood dust that is left over when ambrosia beetles burrow into the wood of dead and infected ʻŌhiʻa trees. The fungal spores that carry ROD can then be easily transported as the dust is taken up by wind and other insects and animals.

However, frass coming in contact with a healthy ʻŌhiʻa tree does not mean that the tree will become infected with the fungal disease.

“In order for Ceratocystis to spread, there has to be a wound, so there’s a lot of factors [involved],” lead author Kylle Roy, former CTAHR researcher and current geneticist at USGS-PIERC, said.

What is Ceratocystis?

ROD is an umbrella term for two different species of the Ceratocystis pathogens, Ceratocystis lukuohia and C.huliohia,Kylle Roy said. C. lukuohia was the focus of the recent publication, being the most virulent of the two. This is the species that is most pervasive on Hawai’i island, and has been shown to be most virulent.

According to Mokiao-Lee, the disease has also been discovered on Kaua’i and there is great concern for further spread throughout other islands. So far only huliohia has been discovered on Kauaʻi, buying researchers some time to look into keeping the spread at bay on the island as that is the slower strain of ROD.

For this study, frass was collected from individual beetle galleries ROD infected trees in Puna, and from these samples 62% of the frass contained Ceratocystis DNA. However, only 17% of the samples actually held viable spores, meaning that they are able to infect other trees. Although this is only a fraction of the collected samples, it implies that the frass produced by ambrosia beetles is another pathway by which ROD can be spread.

Student Involvement

An ʻŌhiʻa seed banking workshop took place on Friday at UH Manoa’s St. John Plant Science Lab where students and community members were given the chance to learn how to identify, collect, and protect ʻŌhiʻa seeds. The workshop focused on the importance of seed banking in the effort to battle the spread of ROD, and provided students that attended with permits for seed collection.

According to William Bleecker, a UH Mānoa senior studying biology and geology & geophysics who attended the workshop, these seed banking efforts are important.

“Even if you never step foot into the forest, in Hawaiʻi the health of our tourism-based economy is dependent on the health of the environment - so in that way, ROD affects everyone who lives here,” Bleecker said. “Workshops like this are great because not only students but any interested or concerned citizen can attend and from it, gain the knowledge and literally the physical tools to have a direct impact on the situation.”

Although there a cure has not yet been discovered, many still see hope on the horizon. According to Mokiao-Lee, researchers are finding that some trees may be resistant to the disease.

“It’s a sad situation but I think it’s good to work with a lot of agencies and partners and people that are very interested in it to try to get a handle on [the disease],” she said. “Although there’s no cure, there’s still hope, and with this whole new thing about the different strains and different varieties that are possibly resistant I think that gives us a lot of hope and that’s a big step in the right direction for this disease.”