Invasive beetle taking toll on O‘ahu palm trees

HONOLULU — The palms along much of O‘ahu’s North Shore are losing their fronds and dying, a harbinger of the fate of others on the rest of the island.

The same is happening in Pupu­kea, where residents are becoming increasingly alarmed at damage to trees on their properties, and in Mokuleia, where a drive toward Kaena Point reveals droopy and missing fronds on longtime coconut trees.

The culprit is the invasive coconut rhinoceros beetle, which has established a decade-long foothold on O‘ahu and is feeding on trees across the isle and propagating in piles of mulch — from the Leeward side to the Windward side and beyond.

“Unfortunately, on O‘ahu the spread has continued for a while,” said Arisa Barcinas, an outreach associate for the environmental organization CRB Response. “It was contained in areas in Central and West O‘ahu in the past couple of years. We’ve seen this widespread to the North Shore and the Windward side.”

Pupukea resident Denise Antolini was saddened to have to cut down a young Samoan palm she had been cultivating in her yard.

She has found the beetles on her property after having mulch delivered, and says her neighbor has found grubs, or larvae, embedded in his soil.

“You drive around the neighborhood, and easily a third of all the palms are dead or dying,” she said. “A lot are cut down. … We’re really hard-hit.”

Waimea Valley’s botanical garden and collection of palms have unfortunately also been affected in the last year, according to conservation manager Parker Powell, including some of the garden’s endangered, native loulus or Pritchardia palms.

The black beetles, which measure up to 2 inches long and have a characteristic horn, bore into the crown of palms and feed on the sap, damaging and potentially killing them. Signs of damage include V-shaped cuts in the fronds.

They were first discovered in coconut tree trimmings near a golf course at Joint Base Pearl Harbor-Hickam on O‘ahu in December 2013, according to the state Department of Agriculture.

Within the next year the beetles were detected at Barbers Point, Campbell Industrial Park, Mililani and Diamond Head.

What seemed like a remote threat years ago — one that residents were reminded yearly of during Invasive Species Awareness Month — is now settling in as a reality.

Beyond containment

The entirety of O‘ahu is now considered infested, beyond containment, according to Barcinas, who is with the CRB Response team.

The team, which is administered through the Research Corp. of the University of Hawai‘i, worked to keep the beetles at bay in earlier years. But what started as an eradication effort became a containment effort, and in early 2023 the beetles were so widespread on O‘ahu that efforts shifted to long-term control and management.

“Unfortunately, what we’re seeing now is that all or almost all areas of O‘ahu have some level of infestations,” she said. “So the entire island, unfortunately, would be considered an infested zone.”

The latest map showing beetle detections in traps includes much of Central and Leeward O‘ahu, the North Shore and pockets of the Windward side.

Some areas are in the early stages with very little damage present, according to Barcinas, such as the swath between the airport and Hawai‘i Kai.

Although they go after mostly coconut, fan, date and royal palms as primary food sources, the beetles also will go after banana and hala trees, taro, pineapple, papaya and sugar cane.

The beetles have destroyed both palms and banana trees at Mililani Agricultural Park.

In the beginning the CRB Response team treated trees, but as more areas became infested, the feasibility of eradication decreased. The team is now focused on decreasing populations around ports to prevent the accidental transport of the beetles off O‘ahu.

While the beetles had been detected only on O‘ahu, they were found at various times in 2023 on neighbor isles: near Lihu‘e airport on Kaua‘i in May and June, in Waikoloa, Hawai‘i Island, in October, and in Kihei, Maui, in November.

An interim rule restricting the interisland movement of palms and other plant materials in Hawai‘i has been in place since October to help contain the destructive CRB from spreading.

Maui and Hawai‘i ˆsland still have a good chance for eradication, said Barcinas. Kaua‘i is in the eradication and containment phase. To date, the beetles have not been reported on Molokai, Lanai and Ni‘ihau.

A wake-up call

The extent of O‘ahu’s coconut rhinoceros beetle infestation is a wake-up call on the state’s need to take swifter action on invasive species to prevent environmental and economic damage.

“We see this again and again with serious invasives, where it’s really small populations,” said Christy Martin, who is with UH Manoa’s Coordinating Group on Alien Pest Species. “Maybe we can still eradicate or at least control it and put in some measures, but people aren’t convinced it’s going to be a problem.”

The same happened with invasive coqui frogs and little fire ants on Hawai‘i Island, which are beyond eradication.

There are various stages of mourning, according to Martin, before people realize “we’re at that point” of no return.

“We weren’t able to put in place any laws or rules to manage the spread around O‘ahu,” she said. “We couldn’t convince agencies that it needed to be done or that it could be done. It just wasn’t done.”

While a swath of O‘ahu, between the airport and Hawai‘i Kai, is still in early stages with very little damage present, spread is inevitable with nothing in place to mitigate their spread on-island, she said.

The spread will continue if people move around mulch and green waste, the primary host material for larvae.

Thomas Irwin, a tree trimmer on the North Shore, says more of his hours these days are spent trying to save or remove infected trees than the regular trimming he used to do, which saddens him.

More than two years ago, he did not see many trees infected with the beetles, he said.

“But in the past year and a half, it was like all of a sudden an epidemic. A horde of them came barreling through the North Shore,” he said, “and worked their way all the way to Crozier (in Mokuleia).”

Oftentimes he takes photos of what’s going on high up in the crown of a tree because the beetles are hard to find. The tree still could be standing, with all fronds except the one in the center, but they eventually fall off in about three to four months.

“Even if your coconut tree or royal looks fine right now, I can almost guarantee I can go up there and find a rhinoceros beetle in it,” he said. “They eat the heart, and once they eat the heart, it’s done.”

Irwin believes the invasive beetles worked their way from Kunia to Mililani and Wahiawa, then the North Shore.

“The wind blows towards the North Shore,” he said. “We’ve lost the battle here.”

At a community meeting May 14 at Kapalama Elementary School, members of CRB Response offered a presentation on the beetles and treatment options.

Treatments will vary depending on the situation, said Barcinas, and can include physical netting or chemical treatments involving injections, soil drenches and crown sprays. There are more options today than 10 years ago.

“Really, the biggest impact is through managing potential breeding material,” she said. “Green waste management is going to be one of the best tools for CRB reduction.”

Managing mulch

That means managing mulch and compost and paying attention to tree stumps, which can be breeding materials for the beetles.

The beetles spend about four to six months as grubs in breeding material developing into adults before they cause damage to palms.

Dexter Kishida, HDOA’s deputy to the chair, said there needs to be a multipronged response to the beetles, including more education and awareness, but that green waste control is one of the most effective ways to break the insect’s life cycle.

“People are starting to notice, especially in heavily infested areas; but in areas that aren’t there yet, we definitely need people to be aware,” said Kishida. “We need folks to not compound the problem by illegally dumping green waste. Use your green bins. Make sure it’s contained and taken to a responsible place that will process them properly.”

The state Legislature has appropriated nearly $20 million to HDOA to combat invasive species, including $1.5 million for the coconut rhinoceros beetle response.

There is no action response plan for the beetles yet, and it is being worked on, said Kishida, but the department has been implementing treatment plans. The response plan is more specifically to gain access to a property to treat for beetles when denied.

HDOA is also enlisting community-based help in its battle against the beetles.

It is offering $200,000 total to Hawai‘i-based nonprofits with viable projects to control CRBs in O‘ahu neighborhoods, and another $200,000 for green waste management projects. Proposals must be submitted to HDOA by noon June 7.

“While in some ways CRB treatments can feel very limited, there are quite a few really interesting ideas out there,” said Kishida. “We’d like to get proposals and … see what we can expand on. That’s one prong — how we can empower communities now and in the future. It is going to be a kakou event. We’re going to have to do this together.”