Posted on: Saturday, December 14, 2002

Bug destroying Moloka'i farms

By Catherine E. Toth
Advertiser Staff Writer

An infestation of caterpillars has been devastating sweet potato on Moloka'i for two weeks, worrying farmers who already are seeing a downswing in production of one of the island's primary agricultural crops.

Hundreds of thousands of sweet potato hornworm caterpillars have been invading Ho'olehua, the central plains near the airport, which has more than 150 acres planted in sweet potato. The caterpillars feed on the foliage; they also eat weeds such as morning glory and biden.

The infestation has been called the worst in recent memory.

"There's nothing the farmers can do right now," said Alton Arakaki, county extension agent for the College of Tropical Agriculture and Human Resources at the University of Hawai'i. "In previous years, the plants would recover ... but this year I'm seeing it worse, and I'm a little concerned."

Arakaki said he expected substantial crop loss and decline in yield, because many of the year-round plants were mature.

Farmers "need to get some relief," he said. "They're going to lose a lot of their investment (in their crops)."

L&R Farms in Ho'olehua, one of the largest sweet potato farms on Moloka'i, had about 40 of its 100 acres damaged by the caterpillars. The farm yields 15,000 to 20,000 sweet potatoes a week.

"It's pretty bad, but we got it sectioned off," said Lynn DeCoit, owner of the 2-year-old farm. "They didn't do damage underground, so we'll recover. But (the damage to the foliage) might stunt the crop."

DeCoit said there were millions of the caterpillars, which can grow to 4 inches. Although she does not like using pesticides, DeCoit said she had no choice; there were too many of the bugs.

"There's nothing you can do about them. You can spray them and you'll wipe them out," she said. "But as much as possible, we want to let nature take its course."

Her father, George Mokuau, lost nearly all 70 acres of his sweet potatoes to the caterpillars, she said. His Ho'olehua farm has been devastated.

"People thought he had mowed it down," DeCoit said.

Sweet potato production has dropped statewide, but on Moloka'i it has fallen significantly in the last five years, from about 11 pounds per acre to less than eight. In 1997, revenue peaked at $432,000; last year, the crop produced just $228,000 on Moloka'i.

Experts reason the decline in production could be caused by climate factors, such as drought, as well as insects, disease and increased competition.

Arakaki said there are about seven to eight caterpillars per square foot, or more than 300,000 per square acre. "It's like locusts coming through the fields," said the UH extension agent, who has been on Moloka'i for more than 20 years. "This is the worst I've ever seen."

Sweet potato hornworms came to Hawai'i in the 1870s, most likely from the Mainland. They are typically black with a horn-like marking on the back end.

Arakaki said Moloka'i is infested with the worms every five to eight years. A decline of parasites, which feed on the eggs, and an abundance of food contribute. Heavy rains last month also could be to blame: The microscopic parasites can "drown" in rainwater, while rain promotes growth of weeds and foliage for caterpillars to eat.

"When there's a lot of food, the population just explodes and it becomes an outbreak," said Bernarr Kumashiro, a taxonomist with the state Department of Agriculture.

Typically, about 90 percent of caterpillar eggs are killed by the parasite Trichogramma, so only a small population survives, he said.

When the caterpillars have exhausted the food supply, they begin to wander. That's what alarmed residents in Royal Kunia and 'Ewa over Thanksgiving weekend, when tens of thousands of caterpillars invaded back yards and streets.

"They were all over my neighborhood," said Guy Yamamoto of Anoiki Street. "They were going through our yard and across the street. I picked up at least a hundred of them."

The state Department of Agriculture has been flooded with calls from concerned, sometimes frantic residents who have never seen such a migration. The latest call was from Kalihi, where a man picked up dozens of caterpillars feeding on his sweet potato plants. One woman called and said her yard was moving.

"There were that many," Kumashiro said.

Reach Catherine E. Toth at 535-8103 or ctoth@honoluluadvertiser.com.