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Fireweed-eating moth becomes established

It’s taken longer than anticipated, but the moth — deemed the state’s best hope of controlling the invasive fireweed that has invaded massive areas of Hawaii pastureland — has become established, a state Department of Agriculture official said Thursday evening.

At Waimea Community Association’s monthly meeting, Rob Curtiss, acting Plant Pest Control Branch manager, gave a brief update about the Madagascan fireweed moth, Secusio extensa, released last year on Hawaii Island and Maui. Here, the release sites were at Kahua Ranch, Ponoholo Ranch and Parker Ranch.

“We thought the establishment was going to go quickly. We were wrong,” Curtiss said. “It took a year and a half before we saw any evidence of establishment, and just this last month, we started getting reports from people in Kona and on Maui in Kula of moths being found in their homes, driveways and garages.”

The callers mistakenly thought the moths were stinging nettle caterpillars and entomologists informed them otherwise. The department is now having a discussion on how to raise public awareness about these beneficial moths. Possible solutions would be distributing a brochure with photos and doing public service announcements

at media outlets, Curtiss said.

For agriculture officials, those calls from places, miles away from where the moth was released, are evidence of establishment success. Curtiss said he went out into the field Wednesday and Thursday, which was also when he discovered the moths in other places where releases didn’t occur. Finding the moths in Kona was not surprising, he added, because the insect comes from a pretty warm place in a low elevation.

“There’s still a lot of things we don’t know about what this insect will do in relation to the different habitats that we have in Hawaii,” Curtiss said. “All of our testing was done in Honolulu, at low elevation and at standard temperatures. So we know that they’ll do well here in Kona, and it should eventually move up here in Waimea because there are higher elevation populations in Madagascar. The population we collected from was from the low elevation.”

Still, Curtiss explained, “it’s going to be years before any real measurable effect here in Waimea or anywhere in the state because there’s so much fireweed there.” When asked by an audience member how many moths are needed to make a significant difference on an acre of fireweed, Curtiss responded, “Approximately eight caterpillars are needed for about every single plant.” The department released an estimated 50,000 to 100,000 moths statewide, he added.

“With this little insect, even though there may be millions out there, we need trillions of them or more,” he said. “Meanwhile, they will be continuing to spread and to get established, feeding on fireweed and other weed-related plants.”

The ranches have been helping rear the small beige-colored moth with black spots, from egg to black fuzzy caterpillar to adult, in incubators with help from the department’s entomologists and university experts. Parker Ranch alone has about 22 cages, Curtiss said.

Since the late 1980s, fireweed has been an increasing problem and has infested more than 800,000 acres, primarily on Hawaii Island and Maui. 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.

This noxious weed has yellow daisy-like flowers and contains pyrrolizidine alkaloids, which are toxic to livestock and cause liver damage. Fireweed competes with other forage plants and takes over pastureland. It’s too widespread, impractical and cost-prohibitive for ranchers to control with traditional removal methods and pesticides. Prior to the moth’s release, fireweed had no natural predators in Hawaii. These moths were also the first biocontrol to be released against fireweed in the world, according to the department.

In 1999, the department began looking for a biological control for the fireweed, also known as Madagascar Ragwort. Biocontrol has been considered the only feasible long-term option for fireweed control by the state and the Hawaii Cattlemen’s Council. The state approved the release of the monh in 2010, but also required approval of a federal permit, finalized on Dec. 6, 2012.

In the future, the department will be working on the three other potential biocontrol agents currently in quarantine: two seed-feeding flies and a stem-boring beetle. Each of the insects appears to attack different parts of the plant. Curtiss said the flies are probably the closest to being released, but the last biocontrol agent took 14 years to release, mostly because of good scrutiny by the federal government. The department is also continuing its exploration of new potential biocontrol agents in Madagascar and South Africa, as well as working with foreign partners like Australia, which has an active fireweed control program.

Of the 175 plants tested, fireweed was the primary plant of the moth’s choice. Its larvae voraciously consume the leaves specifically of the fireweed plants. The insect will also eat three other naturalized weeds, including Cape ivy or German ivy, which is one of the most pervasive and alarming weeds in coastal areas of the western United States.

What will happen when the fireweed is gone? Curtiss said, “They’ll die off. They will feed on these other things we consider weeds like cape ivy. When the food goes down, they’ll go down.”

Other topics discussed at Thursday’s meeting were fire ants, coqui frogs, the Pohakuloa Training Area change of command, course offerings at the North Hawaii Education and Research Center, as well as the International Lunar Observatory Association’s four lunar missions, now in development, and its plans to build a global headquarters and research center in Waimea.

Email Carolyn Lucas- Zenk clucas-zenk@


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