Pesky coconut beetle's backbeat could be its downfall
Aubrey Moore/University of Guam
During the bicentennial of Charles Darwin's birth, let us pause consider a potential application for one of his decidedly less-publicized scientific observations: Oryctes rhinoceros - alias, the coconut rhinoceros beetle - chirps.
Like the grasshopper, the coconut rhino beetle rubs body parts together in its own unique rhythmic way. You can hear what it sounds like here.
It turns out that the beetle is a serious pest in places where coconut palms flourish. That would be spots like southern Asia, the South Pacific, and in parts of Africa. People grow the trees both as valuable agricultural crops for the coconut's meat, milk, and oil, or as (expensive) ornamental plants landscapers use to grace the grounds of tourist resorts. In other places, like Guam, palms are the dominant tree in local forests.
If bug scientist Richard Mankin's work is any indication, that chirping could help knock the bug of its perch on the list of coconut-palm pests.
Dr. Mankin, an entomologist with the US Department of Agriculture, and colleagues have just published the results of an experiment to capture sound prints of the noises the bugs make as they munch, mate, and try to ward off competitors. The ultimate goal is to try to provide locals with a way of detecting these hard-to spot bugs before they have a chance to kill off coconut trees.
It's a bit like the Navy's use of sonar. Sonar operators can identify friend or foe from the acoustic spectra of things as seemingly subtle as the sounds another ship's or sub's propellers make as they churn up the water. With the bugs, the spectra of chirping, or stridulating, may become an early tip-off: You've got bugs in your trees and they are hostiles.
Mankin and his colleagues explain that it's tough to detect these bugs in live trees. They attack the palms at their tops, or crowns, where the fronds sprout and grow. The bugs chomp on the young tissue in the crowns as a way to get access to sap, their ultimate gastronomical goal. If left unchecked, the beetles leave behind a tall, bald, very dead palm trunk.
Using mature beetles in the lab, the team gathered sound prints showing that the critters' chirps come in distinct, easy to identify patterns, interspersed with other background sounds they or their larvae make. In the field, the team also recorded larval sounds, but they were far more random in volume and length.
The scientists also cataloged the sound prints and compared them with the larvae of other species of horned beetles in the region -- an important step toward developing an early warning system for the coconut rhinoceros beetles.
The team's work appears in the current issue of the journal Florida Entomologist. You can read the results here in PDF form.