HAWAI'I KAI — The distinctive two-tone sound of the coqui has been heard echoing in the Kamilo Nui farming valley, causing some concern that their numbers will multiply.

In large numbers, the tiny frogs' nocturnal sound equals a lawn mower. The state Department of Agriculture has confirmed that the sound did come from a coqui frog and the department will be working to eradicate it as quickly as possible, said Janelle Saneishi, department spokeswoman.

However, farmers see the coqui as a friend because frogs eat bugs, and bugs eat plants.

"One or two (frogs) aren't a problem," said farmer Gary Weller. "But a hundred is like trucks with those back-up lights and sounds in your bedroom."

The coqui, a native of Puerto Rico, is small, light-brown to dark-colored, with variable patterns, including a light stripe down the middle of its back. Adult frogs measure up to 2 inches.

Coqui are a problem for plant nurseries that export their products to the Mainland, and the frogs have no known enemies in Hawai'i to keep the population in check. In some areas on the Big Island, population per acre may exceed 10,000 frogs, which consume more than 50,000 insects per night. Officials fear the coqui may endanger native Hawaiian insect populations, including plant pollinators, and compete for food with Hawai'i's native birds.

On O'ahu, the coqui have been contained to Wahiawa, Waimanalo and now Hawai'i Kai, Saneishi said.

The biggest infestation was in Wahiawa, but for the past two months there were no resident calls to report coqui problems.

The sound of the frog was heard recently by Jonathan Gomes, a Mariner's Ridge resident, who regularly jogs along the road through the farm lots in Kamilo Nui Valley. It was just after sunset, when the coqui come out of hiding.

"I was so astounded," Gomes said. "I documented it with my video camera. Hopefully, we can eradicate them quickly."

Saneishi said just two months ago a coqui was captured in the Kamilo Nui Valley. And recently, the hot line, which was set up to deal with concerns about the coqui, received several phone calls from residents who believed they heard them around the Makapu'u area.

"The coqui are more of a noise nuisance," Saneishi said. "On the Big Island, the coqui are more well-established, and it has become a export nuisance. The frogs burrow themselves in the soil."

Reach Suzanne Roig at sroig@honoluluadvertiser.com.