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The Honolulu Advertiser
Posted on: Monday, March 29, 2004

New weapon found to fight coqui

By Jan TenBruggencate
Advertiser Science Writer

State agriculture officials are working toward U.S. Environmental Protection Agency approval to use hydrated lime to control coqui frog populations.

Researchers in Hawai'i have sought ways to control the coqui frog, which has an extremely loud chirping call at night.

Jeff Widener • The Honolulu Advertiser

The product, commonly used as a soil amendment to reduce acidity, is also called slaked lime or calcium hydroxide. It is cheaper and in some ways easier to use than the other common coqui frog-control chemical, citric acid, said Kyle Onuma, the state Department of Agriculture weed specialist in Hilo, Hawai'i, who figured out that hydrated lime might work.

Onuma said he used lime when he grew ginger commercially, and recalled that if it got on his skin, he would feel a burning sensation if he sweated. Since coqui frogs have moist skin, he though it might work against the animals.

It did. Both citric acid and hydrated lime attack the frogs' skin and cause death within a short time, he said.

Researchers across the state have been trying to find ways to control the coqui ever since they began spreading on several islands. The small frogs, known to science as Eleutherodactylus coqui, come from the Caribbean. They have an extremely loud chirping call at night. The noise can be deafening when there are large numbers, and although Puerto Rico residents often say they find the calls calming, many Hawai'i residents find them annoying.

The frogs are spreading on O'ahu, Maui and the Big Island. A Kaua'i population in Lawa'i Valley appears to have been controlled.

Scientists used caffeine to kill the frogs for a time, but EPA registration of that use has expired. The only legal chemical means of control right now is citric acid, which must be sprayed at night in a 16 percent concentration.

However, citric acid can burn plants unless it is washed off within an hour of use.

Hydrated lime, available at any garden shop, is considerably cheaper than citric acid. It can be mixed with water and applied to low plants and the ground during the day, when the frogs may be hidden in leaf litter and rocks, said Larry Nakahara, manager of the Department of Agriculture's Plant Pest Control Branch.

The department has sent its proposal to use the product for comment to the U.S. Fish and Wildlife Service, the University of Hawai'i and the state Department of Land and Natural Resources. Once comments are reviewed and changes made to the documentation, the state will submit a request to the EPA for registration of calcium hydroxide as a pesticide for the coqui.

Some folks are using it now, technically as a soil amendment rather than a pesticide.

"Eventually, the hope is that we get a lot of different techniques for controlling the frogs. In some situations, it might be better to spray one product rather than another," Nakahara said.

For more information about the coqui, check these Web sites:

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.