Invasive coconut rhinoceros beetles spread to Wailuā, Kīlauea – but experts are optimistic

Three months after invasive coconut rhinoceros beetles were first reported on Kauaʻi near the Līhu‘e Airport, more of the species have been found in Kīlauea and Wailuā.

State and local experts recently distributed traps, conducted surveys and performed outreach throughout the Garden Isle in a bid to stop the beetles (Oryctes rhinoceros) in their tracks.

“Right now, we are trying to figure out if there are any other areas that are infested,” said deputy incident commander Keith Weiser of Coconut Rhinoceros Beetle Response, a grant-funded organization based on O‘ahu.

The beetles’ breeding sites in Kīlauea and Wailuā have not been publicly identified by the Kaua‘i Invasive Species Committee – the group that caught the Līhu‘e Airport insects – due to its confidentiality practices.

However, Committee Project Manager Tiffani Keanini said the undisclosed locations are small.

“One is … a decayed coconut stump,” she said. “CRB [coconut rhinoceros beetles] breed in any size of compost or green waste that’s broken down: decomposing stumps, mulch. They need that organic material to lay eggs.”

These are the first detections of the beetles in Hawai‘i outside of O‘ahu. Hopefully, they’ll be the last. According to Weiser, current evidence suggests the invasive insects only recently arrived on Kaua‘i.

“On O‘ahu, they had probably been there at least a couple of years before anybody noticed,” Weiser said. “On Kaua‘i, we caught it within months, possibly within the first month … The only caveat to that is if we find another area that we haven’t seen yet, and there’s old damage. Then we’d have to change that assessment.”

The coconut rhinoceros beetle is a serious pest of palm trees, primarily coconut palms, because the adult beetles bore into the crowns of the palms to feed on the tree’s sap. New, unopened fronds are damaged in this way and when fully opened, may break and fall unexpectedly.

If the beetle kills or damages the growing point of the palm, the tree may die. Secondary fungal or bacterial pathogens may also attack the wounds caused by the beetle, thereby killing the tree as well.

Tree mortality after a beetle attack has been reported to be anywhere from 10 to 50%. Dead trees then become a safety hazard because they may fall unexpectedly after the trunk rots, potentially resulting in bodily injury or property damage.

Responders like Weiser are now waiting for the Hawai‘i Department of Agriculture Pesticide Division to issue an emergency authorization for Kaua‘i.

The experimental use permit will allow a drone operator to apply pesticide to infected palm trees with precision.

“They take the drone up and they stream straight down onto the crown of the palm. It trickles into all the little nooks and crannies that the beetles might be in,” Weiser said. “Within an hour, beetles start falling out of the tree dead.”

Kauaians are eager to see the invasive beetles gone, according to Keanini.

“We have partners within the conservation community; within the natural resource community; agricultural farmers, commercial as well as residential; and different resorts on the island and golf courses around the island,” she said. “And motivated individuals who want to help protect Kaua‘i from coconut rhinoceros beetles.”