It just makes scents: Detection dogs join Molokaʻi search for hidden coconut rhinoceros beetles

When Molokaʻi/Maui Invasive Species Committee (MoMISC) officials identified the presence of invasive coconut rhinoceros beetles (Oryctes rhinoceros) in traps near Kaunakakai, on the Hawaiian island of Molokaʻi, the discovery raised an important question: were the beetles isolated adults, or was the invasive pest already breeding somewhere out of sight?

Coconut rhinoceros beetles are known destroying “niu”, the Hawaiian name for coconut palms (Cocos nucifera). Niu are not only important sources of food and fiber, they’re woven into Pacific Islands culture. They provide medicine, serve as landmarks, and the wood and leaves are a vital part of cultural traditions.

An adult coconut rhinoceros beetle. Forest Service photo.

The invasive beetles see coconut palms as a source of food. They bore into the tree crown, damaging the newer, softer fronds to feed. This damage can stunt the growth of the fronds, reducing the tree’s ability to produce vital nutrients. Multiple feeding events can leave the tree vulnerable to other disturbances such as disease or even kill the tree. But the concern isn’t only for coconut palms. While these beetles are known for feeding on their namesake palms, they also feed on date palms, royal palms, and fan palms, as well as banana trees and loulu palms which are endangered native palms only found in Hawai’i.

The beetles’ feeding habits on culturally and agriculturally significant plants are only half of the problem, however. The other half is detecting them during their larval and pupal stages before they cause significant damage to trees. The immature beetles live beneath piles of decomposing plant material—think mulch, compost, rotting logs, or tree stumps—for months before emerging as adults. These preferred breeding sites, coupled with the relatively long pre-adult life stages of the beetle, make it difficult to get ahead of potential infestations.

Beetle-detecting dogs

Manu, with Hawaiʻi Detection Dogs, arrives on Molokaʻi as part of the rapid-response effort to help locate hidden coconut rhinoceros beetle breeding sites. Forest Service photo.

That’s where man’s best friend enters the story. It may be difficult for humans to spot the beetle larvae and pupae hidden out of sight in mulch piles or fallen logs, but what if dogs could smell them? Kealohanuiopuna Kinney, a research ecologist with Pacific Southwest Research Station’s Institute of Pacific Islands Forestry and Mya Manzo, a former graduate student at the University of Hawaiʻi, are looking into this possible solution.

Kinney has successfully worked with detection dogs to identify asymptomatic 'Ōhi'a trees infected with the fungal pathogens which cause Rapid 'Ōhi'a Death, a disease that has killed more than a million 'Ōhi'a trees across the Hawaiian Islands. “That project really opened my eyes up to what we could do with dogs for early detection,” said Kinney.

When the adult beetles were identified in Kaunakakai, Kinney and Manzo deployed to Molokaʻi, working closely with Molokaʻi/Maui Invasive Species Committee and Hawaiʻi Detection Dogs to survey high-risk breeding sites with Manu, a certified detection dog trained to identify coconut rhinoceros beetles.

Early detection of the beetles is key, a lesson learned after their introduction on other Hawaiian Islands such as Oʻahu, where they remain difficult to manage. For Molokaʻi in particular, the stakes are high as the island is home to the historic Kapuāiwa Coconut Grove where King Kamehameha V planted 1,000 coconut trees, one for each of his warriors, in the 1860s.

Fortunately for Molokaʻi, no coconut rhinoceros beetle breeding sites were identified during the multi-day search in Kaunakakai. However, adult beetles have been identified on at least five of the Hawaiian Islands. Their movements are closely tied with the movement of people and materials, particularly those in the agricultural industry such as potted plants, mulch, or soil. For Molokaʻi, that means continuous searches for breeding-site, palm protection, high-risk material management, and strong biosecurity measures will need to stay in place to reduce the spread of these beetles.

Bringing highly trained detection dogs to every nursey, farm, and grove in Hawai’i is a monumental task. But instead of bringing the dog to the scent, what if you bring the scent to the dog? Kinney and his team are currently testing the viability of capturing pheromones (odorous volatile organic compounds produced by the beetles in each life stage) from field sites to see if the trained dogs can detect the presence of beetles in their pre-adult life stages. If successful, managers and those in the agricultural industry would be able to submit samples for testing, allowing them to get ahead of potential breeding sites.

From left to right, (1) Dr. Michelle Reynolds demonstrates collection of coconut rhinoceros beetles -associated volatile organic compounds from high-risk organic material using a portable vacuum sampling system on the island of Oʻahu; (2) a coconut rhinoceros beetle larva is documented in a mulch substrate with a direct reference odor sample of the larva; and (3) the odor imprinted Getxent® odor-capture tube is removed from the vacuum is secured for canine screening tests off site. Impregnation of the tubes to saturation takes about 4 minutes. Forest Service photos.

Kinney and his colleagues hope to eventually scale up the ability to test more sites. “The immediate challenge is finding hidden breeding sites quickly, but the broader challenge is building tools that can scale CRB [coconut rhinoceros beetles] screening across Hawaiʻi,” Kinney said. “Dogs are powerful biosensors. By pairing their noses with volatile organic compound scent-collection tools, we can test new ways to find hidden larvae and breeding material and screen high-risk materials before CRB spreads.”

While preliminary results are positive, this work is still ongoing, and of course one part of the management equation. In the meantime, the Forest Service Institute of Pacific Islands Forestry will continue to support agencies and organizations working to combat the spread of these invasive beetles, strengthening the state’s biosecurity and protecting Hawaii’s biocultural coastal niu ecosystems.