The Hawaiian island of Oahu has all the ingredients of a tropical paradise. But hiding out on the island is a dangerous invader that has scientists and government officials very worried: the coconut rhinoceros beetle. The beetles' small size and nocturnal habits make it a challenge to keep an eye on them, so scientists are looking into using the latest acoustic technologies to keep an ear out instead.

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The Asiatic rhinoceros beetle or coconut rhinoceros beetle (Oryctes rhinoceros). Both males and females have a disticntive "horn", though the male's horn is more than twice as long as the female's. Image: IsaanHippo/YouTube

In December of 2013, a pest trap at the Pearl Harbor military base in Honolulu caught a single adult beetle. This was the first record of the species in the Hawaiian Islands, and since then, two breeding sites have been identified on golf courses at the base. So far, the bugs don't appear to have spread much farther – and officials want to keep it that way.

Coconut rhinoceros beetles have a nasty habit of digging into the tops of palm trees to get at the tasty sap within, damaging and even killing the trees in the process. They're also known to go after crops such as bananas, sugarcane and date palms. That makes them a danger to agriculture as well as the surrounding ecosystems, not to mention a threat to some of the state's most iconic foliage (this may sound trivial, but tourism is a big deal for Hawaii).

University of Hawaii scientist John Allen and his team have been working on using acoustic detection to identify the sounds made by the beetles, including the noise of their wings in flight and the sounds they make to communicate with each other. Their logic: if we can't spot the beetles to watch over their behaviour, maybe we can listen in on their activity instead.

"Stridulation, or chirping, sounds produced by the beetles have been reported with respect to mating and aggressive male behaviour," Allen said in a press release. The goal is to try to match noises to different behaviors, in males versus females, and at different life stages of the bugs. Through laboratory studies, the researchers have already been able to characterise the sound signature of a distress chirp.

In the end, the researchers hope that listening to the beetles' nightly activities will allow them to identify what they're up to and where they may be going, and perhaps even predict their upcoming movements. This would be a great help in cutting off the insects' attempts to spread across the island.

One of the challenges is to distinguish the signature songs of this species above all the other noises of the night. But Allen is hopeful. "Since this beetle is more massive than other species, the acoustic frequency is less likely to be confused with [that of] other species," he said.

Hawaii is no stranger to harmful invaders. The fire tree is known to outcompete important plants in the islands' ecosystems, and little fire ants not only attack crops, but also people. And then there's one of the world's most successful and deadly invasive species: the dreaded house cat (no joke).

When it comes to the coconut beetles, which are native to Southeast Asia, officials aren't sure how they made it to Hawaii in the first place, though they were most likely carried over via aircraft. The bugs' presence wouldn't be so concerning if they didn't already have a terrifying destruction record.

Damage from invasive coconut rhinoceros beetles in Guam. Image: Aubrey Moore, Flickr

After the beetles made it to Palau in the 1940s, they managed to wipe out half the palm trees on the island. They were introduced to Guam in 2007, and spread across the entire island within just three years, despite numerous attempts to contain them. Similar invasions have happened in Malaysia, American Samoa and several other islands.

Hawaii certainly doesn't want to be next on that list, and United States officials are also worried the bugs might hitch a ride over to Florida or California, which also maintain important palm oil and date crops, foods the beetles would love to get their jaws into.

On other islands, strategies for containing the insects have included chemical pesticides as well as natural viruses and fungi to attack the beetles in the wild. But many of these methods are not approved for use yet in the United States.


Top header image: Durham Field Office, Flickr