Moths, ‘eating machines,’ defense against fireweed

PUKALANI – The state Department of Agriculture plans to release hundreds of “eating machines” next week to combat the thousands of acres infested with invasive Madagascar fireweed that is harmful to cattle and horses.

In the joint bio-control program between the Agriculture Department, the University of Hawaii and the Hawaii Cattlemen’s Council, the Madagascan fireweed moth will be released on ranches around Maui.

“We plan to release a million fireweed moths by the end of the year,” said Darcy Oishi, Agriculture Department acting plant pest control chief, to more than 50 ranchers and others members of the community Wednesday night at the Mayor Hannibal Tavares Community Center. “It’s going to take a lot of time to tell how effective this is going to be . . . but this is a big first step in active management, and I want to thank the ranchers for being patient.”

After 13 years of research, the Agriculture Department and the Institute of Pacific Islands Forestry have found that the moth in its early larval stage may help slow the vigor of the fireweed.

“They are eating machines,” said Mohsen Ramadan, a researcher with the Agriculture Department. He said that the caterpillars eat everything green on the plant.

“This is what makes the plant weak,” he said.

In 1999, Ramadan traveled to Africa in search of a natural predator for the invasive plant. Starting in Egypt, he made his way down the continent but found no signs of the plant.

Upon reaching South Africa, he found small populations of fireweed – no more than 100 plants – that had a variety of insects feeding on them.

During his studies, which tested a variety of insects and plant species, the fireweed moth emerged as a favorite because its larvae fed and thrived on the fireweed – and virtually no other plant, he said.

In one test, moth caterpillars were placed on six plants other than the fireweed and forced to survive. Excluding the common sunflower, which yielded live adults, no larvae survived beyond the first larval stage, he said.

In testing with sunflowers and fireweed only, the caterpillars exclusively chose the fireweed. He said those results negated theories that the moth would move on to other plants.

To quell rancher and community concerns, Ramadan added that the moth larvae that fed on the sunflower did not survive more than one life cycle. He explained that male fireweed moths use toxins produced by the fireweed to attract females, meaning that their ability to reproduce is controlled by the abundance of fireweed.

Australia, which has suffered from fireweed infestations, tried to use the moth as bio-control, Oishi said, but the results were unsuccessful due to other indigenous plants too closely related to the fireweed plant.

“We’re fortunate that we don’t have any closely related plants, here in Hawaii,” he said.

On the Big Island, fireweed moths already have been released. Teams from the University of Hawaii’s College of Tropical Agriculture and Human Resources have placed about 3,000 cocooned moths on Big Island ranches since January, said Mark Thorne, CTAHR state range and livestock specialist.

Thorne estimated larvae to be in the thousands on the Big Island, with more on the way.

“Temperatures are a factor in population growth and movement through the larval stages,” he said in anticipation of the warmer summer weather.

The responsibility of raising the initial group of moth cocoons will fall on the ranchers. Each ranch will receive 50 to 100 cocoons, which they must raise in cages for the first life cycle.

The cages are to aid in the survival and the initial mating of the fireweed moth. Thorne suggests the cages be about 2 feet high, 3 feet wide and 4 feet long, and be placed in an area with an abundance of fireweed.

Ranchers should monitor plants and moth density once the creatures mature because disease is a threat if moth populations became too dense. After the first life cycle of the moth, the ranchers will remove the cages and let moths fly free.

The beige-colored fireweed moth, native to Madagascar, feeds on fireweed nectar and metabolizes a harmful alkaloid toxin produced by the plant. The toxin has been found to poison livestock, including cattle and horses, causing liver damage and sometimes death.

In a report titled “Fireweed Control: An Adaptive Management Approach” provided by CTAHR, researchers found cattle to die in as little as four weeks after consuming more than one-fifth of a pound of a similar plant with the same toxin. The report found common side effects from alkaloid poisoning to include abdominal pain, weakness and constipation.

Scott Meidell, vice president and general manager at Haleakala Ranch, said that he is not aware of any livestock poisoned by the plant, but its prevalence has significantly lowered the amount of quality forage.

“It crowds out the forage and makes the cattle much less productive,” he said.

Since its introduction in the early 1980s, the fireweed can be found from sea level to the upper slopes of Haleakala. With outbreaks also on Molokai, Lanai and Kahoolawe, more than 400,000 acres of rangeland is infected in Maui and Hawaii counties. Currently, fireweed infestations are relatively small on Lanai and Molokai and are eradicated through pesticides and manual removal. Those islands are currently being assessed for bio-control measures.

Although the Big Island accounts for much of the affected land, Greg Friel, livestock manager at Haleakala Ranch, said about 3,000 acres of his ranch is infested with fireweed.

“It’s a major problem. It’s not as bad as the deer, but it’s bad enough,” he said referencing the thousands of axis deer that have wreaked havoc on Upcountry farms, ranches and backyards for more than a decade.

With fireweed moth rearing facilities on the Big Island and Oahu, the program hopes to have a similar facility in Kula.

“On Maui we need to ramp up production,” Oishi said to the ranchers at the meeting. “Supply is primarily coming from Oahu . . . but get your cages ready.”

* Chris Sugidono can be reached at