Judas Beetles: How Coconut Rhinoceros Beetles Are Betraying Each Other’s Secrets
By Josh Lancette
It starts with the search for a mate. It ends with betrayal. And death. And a toppled crime empire.
How? Someone is wearing a wire from the feds.
Specifically, that someone is a coconut rhinoceros beetle, Oryctes rhinoceros.
Its empire? An army of its kind aiming to destroy palm trees in Southeast Asia and several Pacific Islands.
And the wire? Technically, it’s a radio tracking device, placed on beetles by researchers from the University of Guam, Eastern Mennonite University, and the U.S. Agricultural Research Service.
The coconut rhinoceros beetle is an invasive pest that’s devastating palm trees by boring into the crowns of the palms to feed on sap, thus killing the trees. The beetles are hard to control, and techniques such as pheromone trapping, biological control, or sniffer dogs have been ineffective or expensive. One of the most effective strategies for controlling the beetle is finding and eradicating potential breeding locations. However, breeding sites are often cryptic and found in a wide variety of locations, so discovering the sites is easier said than done.
So, the researchers decided to try a new method. Dubbed “the Judas technique,” it involves capturing adult beetles, placing radio tracking devices on them, and then following the tagged beetles to breeding locations using the tracking device. In preliminary tests, the results of which are published in Environmental Entomology, the technique was effective for finding cryptic breeding sites.
“Ours was a feasibility study, and the technique definitely works,” said Aubrey Moore, one of the researchers and an author on the paper. “The Judas beetle technique could become an important tactic for coconut rhinoceros beetle eradication, which requires that all active breeding sites are found and destroyed.”
One marker of success is that the technique allowed the discovery of breeding sites that otherwise would have gone unknown or unnoticed.
“A damaged breadfruit tree would not have been a place we would have thought to look for beetle aggregations, and yet we found several beetles in a broken branch courtesy of one of our released beetles,” said Matthew Siderhurst, another research and author. “Furthermore, none of our tracked beetles ended up inside one of the many beetle traps in the areas where we released them. In two cases when we did track beetles to trap locations, we ended up finding the tagged beetles under the barrel traps, not inside them.”
Even though the experiment was a success, more studies need to be done to determine whether the technique can be used effectively on larger scales. For now, this study serves as a good proof of concept.
“What is needed is a scale-up study run over a longer period of time,” said Siderhurst. “One of the ways we envision that this technique could be applied is as part of a rapid response eradication program. In concert with other control strategies, Judas beetles could be used to find and delimit the infestation and help to mop up beetle breeding sites that might be at relatively low density near the end of an eradication effort.”
While the authors believe this is the first study using the Judas technique with insects, the Judas technique is not altogether novel. The method has been used extensively in mammalian species, such as feral goats, as well as with fish and birds.
Josh Lancette is Manager of Publications at the Entomological Society of America.