Damage linked to the palm tree-killing coconut rhinoceros beetle has become more obvious in urban Honolulu, according to city officials.
Recent plantings at new privately owned building developments in Kakaako and Ala Moana show the telltale signs of CRB infestations — boreholes 2 inches or bigger in palm trunks, V-shaped or scallop-edged palm fronds and generally unhealthy-looking trees overall.
CRB breeding populations also are being discovered along the palm-rich corridor extending from Iolani Palace to Diamond Head Crater, the city Department of Planning and Permitting asserts.
To combat the problem, DPP says it’s strengthening efforts to preserve the health of the island’s urban landscapes.
“The DPP is concerned about CRB for many reasons, but primarily we are concerned about the potential rapid loss of palms in our community forest and the related safety hazards that result from damaged or dead palms falling unexpectedly,” Alexander Beatty of DPP’s Urban Design Branch, told the Honolulu Star-Advertiser.
The department’s main focus is on new development and replacement of landscapes, he said.
“The DPP has limited authority over private landscape; therefore, we are focusing our efforts in street trees, which require DPP approval, and in the special districts, which often require approved landscape plans,” Beatty added.
In March 2024 the department implemented a policy aimed at slowing the spread of CRB until effective treatments are available. The policy is focused on areas under DPP’s direct authority and includes the following measures:
>> Prohibiting palms from fulfilling street tree requirements.
>> Discouraging the use of palms to meet landscaping requirements.
>> Limiting the use of compost, wood, tree chips and mulch that may harbor CRB.
>> Requiring compliance with the state Department of Agriculture’s interim rule restricting the movement of CRB host materials.
>> Mandating an invasive species management plan for affected developments.
>> Ensuring damaged palms are replaced with tree species that are not susceptible to CRB.
Despite efforts, DPP continues to see new urban landscapes dominated by palms, such as coconut and loulu. The department encourages residents and developers to consider alternative tree species.
Native and Polynesian- introduced species featured on the city’s Street Tree List offer a range of sizes and benefits. Those plants include alahee, ohia, hau, milo, kou, kukui, lonomea, manele, variegated hau and kamani.
Canopy trees favored
Areas in urban Honolulu — including those with special districts — continue to have spots where coconut palms are common. The Hawaii Capital Special District, the Punchbowl Special District, the Thomas Square Special District, the future Transit Oriented Development Special Districts and the Waikiki Special District are among the locations, according to Beatty.
“These areas rely heavily on palm plantings, and that reliance poses a real threat to our urban forest,” he said. “It also creates an elevated hazard since these are more pedestrian- oriented and highly trafficked areas. Kakaako is also in this area but is not under the jurisdiction of the DPP for landscaping.”
He noted coconut trees themselves are not effective canopy trees either.
“Canopy trees offer exceptional public benefits relative to their cost — providing shade, mitigating the urban heat island effect, managing storm water and enhancing the pedestrian experience, especially when diverse species are planted,” he said.
A result of this effort has been a renewed focus on incorporating Hawaiian canopy trees, according to Beatty.
“Several projects in Waikiki have already replaced palms in their landscape plans with more canopy trees,” he said. “For example, Hilton Hawaiian Village plans to significantly increase canopy coverage around the edges of their campus, particularly near the lagoon.”
Another hope is tree growers will increase availability of these species so they can be used more often and at larger scales, he said.
“We also hope that other projects, including those in Ala Moana and Kakaako, will see the wisdom of diversifying the planting to make a more resilient community forest and take action on their own,” he said. “Damaged trees that have been treated are still a hazard, and should be replaced.
“We understand that this will require a shift in thinking from the community, including developers and landscape architects,” he said. “However, planting shade trees and replacing damaged palms with shade trees will help create a more resilient community forest.”
As far as DPP’s efforts, no city funds have been spent to quash the CRB threat. “We are operating within the existing regulatory framework of zoning and street trees,” Beatty said.
Jeanne Rice, an Ala Moana-Kakaako Neighborhood Board member, said the CRB problem is a threat to all of Oahu, not just in the vicinity of her longtime residence near Ala Moana Regional Park.
“I think everyone needs to be vigilant regarding these beetles. I’ve seen the damage they can do personally; it’s such a shame, and I know the state has been trying for many years to eradicate them too,” she added.
Few success stories
First detected in Hawaii in 2013 after being discovered at Joint Base Pearl Harbor-Hickam, the ravenous beetles have spread to different parts of Oahu where coconut palms and other palm varieties have become their main source of food.
The insects are native to Africa, China, Myanmar, India and Southeast Asia.
Adult beetles are black, 2 inches long and have a visible horn. They typically take wing at night and can fly up to 2 miles if looking for a food source. Female beetles might lay 50 to 140 eggs in their lifetime, which is four to nine months. And although the insects don’t bite, they can carry disease and should not be handled with bare hands, if possible.
CRBs create bore holes in palm trees that can lead to an individual tree’s untimely demise. They then eat palm fronds to the point where the foliage is unable to photosynthesize, or turn sunlight into chemical energy for the tree to grow or survive.
As insecticides and other bug-stopping methods have proved only moderately effective in controlling the spread of CRBs, the City and County of Honolulu has worked to identify and remove dead or dying coconut palms at city-owned parks, as such trees can become CRB breeding grounds.
Many of those parks are located along the Leeward Coast and the North Shore.
“Really, the unfortunate truth is it’s going to get worse before it gets better,” said city Department of Parks and Recreation spokesperson Nate Serota, during an October news conference at Haleiwa’s Bill and Peggy Paty Kaiaka Bay Beach Park, where many palms needed to be cut down due to CRB infestations. “We’re going to have to start removing more and more of these palms, really out of concern for public safety.”
But, according to Serota, CRBs don’t stop at just palm trees.
He said the destructive insects threaten “heritage plants” as well, including taro and other staples brought by the Polynesian voyagers who first populated the Hawaiian Islands centuries ago.
The Coconut Rhinoceros Beetle Response Team, administered through the University of Hawaii and funded by the U.S. departments of Agriculture and Defense, is also part of the effort to control the beetle.
At the same news conference in October, Keith Weiser, a CRB Response Team member, said “success stories” in fighting these insects are few and far between and mainly occur only in urbanized areas. He noted that a combination of netting and insecticides — typically with the use of plant-based pyrethrins — can be used to control CRB infestations.
For more information on DPP’s program, visit honolulu.gov/dpp/.
