Mamaki-munching pest highlights need for prevention

KIA'I MOKU

The caterpillar of the ramie moth can be identified by its coloration — black with orange dots and white hairs — as well as its behavior — it “hisses” when approached. Report sightings to 643PEST.org. -- Department of Land and Natural Resources photo

Last October, Keahi Bustamente was looking for rare snails in Olowalu Valley when he noticed a mamaki plant showing signs that something had been eating it. A quick look revealed the culprit was a black caterpillar. He plucked the unfamiliar insect in hopes he had found something new — perhaps a native species. Bustamente is an invertebrate biologist with the Pacific Cooperative Studies Unit. He works with the Department of Land and Natural Resources and spends his days scouring the forests for native land snails.

He couldn’t identify the larva and started asking colleagues on Maui and Oahu. An entomologist on Oahu guessed that it was from a ramie moth, never before found in Hawaii, but to confirm the identification, Bustamente had to raise the caterpillar to the adult moth stage. A brown-and-black moth with a 3-inch wingspan emerged — it was indeed the ramie moth.

This new moth, Arcte coerula, is native to the Philippines and dines on plants in the nettle family (Urticacea). The moth is large and a strong flyer, but it most likely arrived on our shores as a hitchhiker. Uninvited, this interloper is now munching its way through mamaki in our forests.

Mamaki is traditionally used in Hawaiian culture for medicinal tea and cordage. Increasing interest in the plant has led it being grown commercially for tea. In the forest, mamaki serves to stabilize stream banks. Mamaki supports over a dozen species of native insects, including leaf miners, moths and beetles, and the Kamehameha butterfly, which is reliant on mamaki.

It’s not just mamaki that is at risk. The caterpillar of the ramie moth has been found on other plants related to mamaki, including ma’aloa (Neraudia sericea), an endangered plant on the verge of extinction.

A few weeks after Bustamente found the caterpillar in Olowalu, a native-plant grower reported finding it in Olinda and Ulupalakua; sightings from Waiehu, Iao Valley and the mountains of West Maui soon followed. It quickly became apparent that the ramie moth was already too widespread to be removed from Maui.

The ramie moth is only the latest in a host of pest insects. Every year, over a dozen new insects arrive in Hawaii. Some turn out to be serious invaders forever altering life in the islands. Little fire ants, coconut rhinoceros beetle, varroa mite, coffee berry borer and naio thrip are recent examples. These troublemakers threaten native plants and animals, the function of our environment, our relationship with nature. Once established, they impact cultural practices, recreation and the livelihoods of the residents of Hawaii, jeopardizing tourism and agriculture.

“At any point, some new plant or animal can come in and forever change Hawaiian ecosystems in a way we can never recover,” says Bustamente. The arrival of yet another pest highlights the need for increased prevention efforts. The Hawaii Invasive Species Council in cooperation with state and federal agencies developed the Hawaii Interagency Biosecurity Plan. The plan lays out specific steps needed to improve biosecurity in Hawaii. The plan needs legislative support and funding to be implemented.

It’s still too early to tell what the impacts of the ramie moth will be, but Bustamente and others are concerned. “The caterpillar can hammer a mamaki plant,” says Bustamente, who has found over 100 individuals on a single plant. Even though it’s unlikely all will survive to adulthood, it’s during their caterpillar stage that they damage mamaki.

If you have mamaki or other nettle-family plants in your yard, be alert to the threat of the ramie moth. Look for a black caterpillar (sometimes yellow) with bright orange spots and white hairs. Be careful not to confuse the ramie moth with the native Kamehameha caterpillar. The Kamehameha caterpillar is green for most of its life but is black immediately after hatching. The behavior differs as well — the ramie moth caterpillar rears up and spits to defend itself.

Report sightings to the statewide pest hotline, either by phone, 643-6245, or online, 643PEST.org. You can learn more about plans to improve Hawaii’s protection against the arrival of new pests at the Hawaii Invasive Species Council’s website: dlnr.hawaii.gov/hisc/plans/hibp/.

* Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. “Kia’i Moku,” or “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.