Moths versus fireweed State uses biological control to help protect pastures
Hawaii ranchers are getting buggy, and farming miniature “livestock” is generating a great deal of hope.
Kahua Ranch President Tim Richards said his 8,500-acre ranch on Kohala Mountain has been rearing the Madagascan fireweed moth, Secusio extensa, for a month in incubators with help from state Department of Agriculture entomologists and experts from the University of Hawaii’s Mealani Experiment Station. It takes 40 to 45 days for an egg to become an adult moth, Richards said.
The small, beige-colored moth will be used to help control a fast-growing invasive weed known locally as fireweed, or Madagascar ragwort, that’s toxic to livestock and has caused havoc on the state’s prime pastureland.
On a rainy, windy Wednesday morning, roughly 200 moth larvae, or caterpillars, were released in a 3-foot-tall enclosure, covering an approximately 5.5-foot by 5.5-foot area of fireweed on Kahua Ranch and. Throughout the day, an additional 800 larvae were released in similar enclosures at Ponoholo Ranch and Parker Ranch, said Darcy Oishi, the Department of Agriculture’s Biocontrol Section chief.
Other releases are planned elsewhere, including on Maui in a few weeks.
Since the late 1980s, fireweed has been an increasing problem and has infested more than 850,000 acres, primarily on Hawaii Island and Maui. With the support of ranchers and others, the Department of Agriculture is planning to release more than 1 million moths a year, Oishi said. A rearing and release program has been developed in collaboration with ranchers, Department of Agriculture, and the UH College of Tropical Agriculture and Human Resources. Those interested in getting involved locally should contact the Mealani Experiment Station in Waimea, he added.
The fuzzy black larvae voraciously eat fireweed leaves — something they did “with great vigor” in controlled conditions of the state’s quarantine laboratory, said Mohsen Ramadan, the Department of Agriculture’s exploratory entomologist. During tests, the moth only fed on the fireweed and other weeds, making it appropriate to release. The moth could be raised with ease, so much so that they were released in buckets Wednesday, he added.
How the moth will respond in nature, such as the cold, remains to be seen. The Department of Agriculture plans monthly monitoring of release sites and moving enclosures as the infestation of moths increases, Oishi said.
Ramadan was proud of his “babies,” which he discovered in southeastern Madagascar and has researched with his colleagues for more than a decade. He called Wednesday’s release “a great and happy day for Hawaii, which is the first to release a biocontrol agent against fireweed in the world.”
Ramadan said this insect is not the save-all-answer to the fireweed problem. The moth will not eliminate the fireweed. Instead it will slow the weed’s progress in taking over vast areas. He said the department is also testing three to five other potential natural enemies of fireweed for future release. Each of the insects appears to attack different parts of the plant.
Oishi also stressed the moth was not the silver bullet, but “another tool and a new day” to manage and control the weed, and help preserve Hawaii’s ranching heritage. He said current research methods thoroughly test potential biocontrol agents prior to release to ensure they only attack the target and not other native or beneficial plants or animals. “It’s a safe, highly scrutinized, solid process,” he added.
Prior to the moth’s release, fireweed had no natural predators in Hawaii. It is believed the weed came to the island in mulching material imported from Australia, where it’s a serious pest. Resistant to drought, each plant produces approximately 30,000 seeds annually that are easily spread. If left unchecked, officials had estimated fireweed could spread to an additional 1.5 million acres in the next 10 years, Richards said.
In certain areas, the noxious weed has reduced forage production by as much as 60 or 70 percent. In other pastures, there has been a 20 percent reduction, Richards said.
The invasive plant contains alkaloids. When ingested by livestock, it causes liver damage or failure and, in severe cases, death, particularly of young animals. The disease is progressive, with symptoms and death occurring weeks or months after consumption. However, sheep, which ranchers have used as a control method, are able to tolerate the poisoning because they possess a bacteria that detoxifies the alkaloids before absorption, Richards said.
For years, ranchers have been losing the battle against fireweed, using chemical and mechanical means in an attempt to control it. But because of the immense and widespread infestation, those methods are expensive and impractical, Oishi said.
Early on, Richards said the Hawaii Cattlemen’s Council agreed biocontrol was the only feasible long-term option for fireweed control. The council funded the first exploratory trips by state entomologists to search for the best biocontrol agent, which began in 1999.
Hawaii Department of Agriculture officials and ranchers repeatedly praised the release Wednesday as an exciting joint collaborative effort between them and the University of Hawaii.
For more information, visit hawaii.gov/hdoa.a Kona