Coconut rhinoceros beetle grubs found on Big Island

Coconut rhinoceros beetle grubs have been found at a residence in Waikoloa Village on Hawai‘i Island.

This is the first discovery of the invasive beetle on the island.

On Oct. 11, the resident found five large grubs (larvae) in a decaying palm tree stump on the property and reported it to the Coconut Rhinoceros Beetle Response Project. Staff from the Hawai‘i Department of Agriculture responded to the site and collected the specimens which were sent to a University of Hawai‘i laboratory in Honolulu where a DNA-based test was used to identify the grubs as coconut rhinoceros beetles.

On Wednesday of this week, the resident reported finding one more grub on the property. No other grubs or adult coconut rhinoceros beetles have been detected so far on Hawai‘i Island.

Department of Agriculture crews on Hawai‘i Island and coconut rhinoceros beetle response staff from O‘ahu have surveyed the immediate area and have not found additional coconut rhinoceros beetle damage. A multi-agency team will continue to survey the area.

Additional pheromone traps, used for early detection of infestations, are being deployed from Waikoloa Beach to Waimea, as well as other areas around the island. Surveillance for coconut rhinoceros beetle has been ongoing on all islands, including traps at airports, harbors and other strategic locations. Department of Agriculture staff are also trying to trace the origin and the pathway of the grubs found in Waikoloa.

Residents are encouraged to go to the Coconut Rhinoceros Beetle Response website at: https://www.crbhawaii.org/ to learn more about how to detect the signs of coconut rhinoceros beetle damage, how to identify coconut rhinoceros beetle life stages, and how to report any suspected signs of damage or beetles/grubs via the coconut rhinoceros beetle reporting feature.

Reports of possible coconut rhinoceros beetle infestation may also be addressed to the Coconut Rhinoceros Beetle Response team at 808-679-5244, email info@crbhawaii.org or the state’s toll-free Pest Hotline at 808-643-PEST (7378).

Coconut rhinoceros beetle grubs live in decomposing plant and animal waste and may have been inadvertently transported across O‘ahu and to neighbor islands in bags of compost or mulch. Adult coconut rhinoceros beetles prefer to feed on coconut and other larger palms, and are a major threat to the health of these plants.

Residents on all islands are asked to be vigilant when purchasing mulch, compost and soil products, and to inspect bags for evidence of entry holes. Adult beetles are about two inches long, all black and have a single horn on their head.

The coconut rhinoceros beetle is a large scarab beetle that was first detected on O‘ahu in 2013. The beetle has since been detected in many neighborhoods on O‘ahu, and was detected on Kaua‘i in May 2023 where collaborative eradication efforts continue. Last week, several agencies were involved in the pesticide treatment of palm trees via drones at a Kaua‘i golf course. More than 90 palm trees were treated and 40 adult coconut rhinoceros beetles were killed. Additional treatment efforts will continue on Kaua‘i.

Last month, a dead adult coconut rhinoceros beetle was found in a compost bag at a Maui big-box store. No other coconut rhinoceros beetles have been detected on Maui.

Coconut rhinoceros beetle is a serious pest of palm trees, primarily coconut palms, as 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 coconut rhinoceros beetles kill or damage the growing point of the palm, the tree may die.

Secondary fungal or bacterial pathogens may also attack the wounds caused by coconut rhinoceros beetles, thereby killing the tree as well. Tree mortality after coconut rhinoceros beetle attack has been reported to be anywhere from 10% to 50%. Dead trees then become a safety hazard as they may fall unexpectedly after the trunk rots, potentially resulting in bodily injury or property damage.

Coconut rhinoceros beetle is a major pest of palms in India, the Philippines, Palau, Fiji, Wallis, Nukunono, American and Western Samoa and Guam. It is still not known exactly how the beetles arrived in Hawai‘i.