Coqui nearly silenced at O'ahu, Kaua'i sites
By Jan TenBruggencate
Advertiser Science Writer
Wildlife officials say they're having heartening success using citric acid — the stuff that gives lemons their bite — to control noisy coqui frogs.
Advertiser library photo • Sept. 8, 2003
The two most significant populations on O'ahu and Kaua'i appear close to being wiped out, and although the frogs are so widespread on Maui and the Big Island that eradication seems unlikely, officials feel it may be possible to control them in specific areas where people live.
Spraying citric acid has helped reduce coqui colonies at Schofield on O'ahu and Lawa'i on Kaua'i, officials say.
Coqui frogs are so small they fit on top of a quarter, but the voices of calling males can reach 90 to 100 decibels. In dense numbers, the noise can interrupt sleep and other activities, residents have reported.
"It's just growing exponentially, and established populations are getting denser and they are continuing to spread out," said Meg Jones, a Big Island education officer with the University of Hawai'i's College of Tropical Agriculture and Human Resources (CTAHR).
Big Island officials have invited the public to learn how to track down the frogs and to spray them with citric acid. The state is loaning out spray tanks for communities to use. The acid, which is weak enough that it does not burn human skin, is toxic to the frogs.
"We're working with the communities, and you'd be surprised what they come up with. They're learning to locate the males and capture them by learning their behavior," said CTAHR entomologist Arnold Hara, an organizer of the Coqui Frog Working Group.
The frogs, native to Puerto Rico, are believed to have arrived in the Islands unnoticed in potted plants imported to local nurseries. Jones said it now appears they're hiding in mulch and hitchhiking on vehicles and construction equipment.
On Maui, 40 infestation sites have been identified, most of them in lowland areas such as Lahaina, Kihei and around the coast to Ha'iku in East Maui. Most citric acid spraying is being done by the Hawai'i Department of Agriculture and the Maui Invasive Species Committee.
There, an effort to involve local communities is also on the radar screen.
"We've talked about doing a public relations campaign to educate people about the sound and what they can do. We'd like to get funding to package citric acid in small packages to mix with water," said Mele Fong, education specialist with the Maui Invasive Species Committee.
There are at least three small infestations in or around nurseries on O'ahu, but the primary wild colony has been on a roughly 9-acre site near Schofield Barracks. Crews have now sprayed about 1,100 gallons of citric acid, "and we're in a mode where we're doing mop-up," said Scott Williamson, an invasive species technician with the state Division of Forestry and Wildlife.
"We've reduced the calling frogs way, way down, and it's to the point where you're after individual frogs," he said.
Crews on Kaua'i hope they have entirely stopped the spread of a colony in Lawa'i. Residents there don't hear the frogs any more, but they worry that hatching eggs will re-establish it.
"We haven't heard them for a couple of weeks, but they often show up again when it starts raining," said Lawa'i resident Steve Smith.
The future of coqui control could be community members heading out whenever they hear one, to try to catch it by hand or spray it with citric acid.
"Anyone with a little Windex squirt bottle of citric acid can do it," Williamson said.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
