In the hills above Hāna, Nāhiku, and Keʻanae, the Maui Invasive Species Committee (MISC) crew hikes day in and day out looking for and pulling miconia plants. The team is about to grow as a kaleidoscope of golden yellow butterflies descends to assist with control.
Miconia is a notorious invader of Hawaiian forests. A single plant can produce 8 million seeds. Miconia seeds grow quickly into large plants with huge leaves that block out the sunlight preventing other plants from germinating. Miconia’s shallow roots do little to stabilize the soil. Eventually, miconia becomes the only plant in the forest; invaded sites are known for landslides and erosion that muddies streams and buries reefs.
When biologists first found this invasive plant growing in Hawaiʻi, it was a call to action. Retired state forester Bob Hobdy helped address miconia in East Maui in the early 1990s. Initially, crews focused on the area above Hāna known as “the core,” but reports started pouring in from multiple locations across East Maui. “The idea of eradication [removing every plant from the island] was set aside,” says Hobdy. “It was not feasible.” The shrubby tree was scattered from Huelo to Kipahulu, with two major infestations in Nāhiku and Hāna. Too widespread to eradicate, but too damaging to ignore, the long-term solution was biocontrol: the researched introduction of a natural enemy specific to miconia that could lessen the impact and spread of the plant.
Over the last 27 years, crews have worked to contain this invader in the field. It’s been a success: miconia never reached the West Maui mountains and it’s rare to find a plant along Hāna Highway. Meanwhile, researchers in Hawaiʻi and South America have sought out and tested insects and plant diseases in hopes of finding something that will permanently undermine the plant’s invasiveness.
In 1997, ecologists released a fungus that eats holes in miconia’s large purple leaves. In Tahiti, this fungal natural enemy opened up the canopy so that other plants could grow, but fungus didn’t have the same effect here in Hawaiʻi. The search continued.
Tracy Johnson of the U.S. Forest Service has worked to find miconia’s natural enemies for 20 years. He’s hopeful about another miconia pests, a tiny yellow butterfly that lays its eggs on the leaves. The caterpillars hatch out and to dine on the umbrella-like leaves until they become adults. “Itʻs very specific to miconia,” says Johnson. “We know from observation in Costa Rica and in Hawaiʻi that it’s one of the most damaging insects to leaves of the plant.”
Miconia’s huge leaves are major problems: they act like tarps, shading out the understory, collecting raindrops and funneling them to the ground. In comparison, native ōhiʻa and koa trees have clusters of little leaves that break up rainfall into small drops that gently water the understory. The raindrops that roll off of miconia leaves are some of the largest measured They hit the ground with extra force—and since the ground beneath miconia is bare—they contribute to increased erosion. In fact, scientists have found that erosion is greater in a miconia-invaded forest than if the rain fell on bare soil.
“Itʻs (the golden miconia butterfly) very specific to miconia,” says Johnson. “We know from observation in Costa Rica and in Hawaiʻi that it’s one of the most damaging insects to leaves of the plant.”
Enter the golden miconia butterfly, Euselasia chrysippe, —a voracious leaf eater. Johnson and colleagues from the University of Costa Rica tested E. chrysippe with 73 different plants to see what the caterpillars would feed on. In a process called no-choice testing, caterpillars are placed in a petri dish with a leaf of the plant being tested. When forced to feed on other plants, they died; only Miconia calvescens and closely related plants in the melastome family can sustain them. This is good news since Hawaiʻi has no native melastomes.
After gorging on miconia, E. chrysippe caterpillars metamorphose into butterflies and seek out another miconia plant on which to lay their eggs. Like the MISC miconia crews, they’re really good a finding the pesky plant.
The golden miconia butterfly could help halt Hawaiʻi’s miconia invasion. But there is still more to be done. Johnson is investigating other potential natural enemies, particularly an insect that eats miconia seeds. Until a suite of effective and safe natural enemies exists to control miconia, crews from MISC will continue combing the hillside in search of miconia. Any sightings of miconia can be reported to MISC at 808-573-6472.
April 2020 Update: The Hawaiʻi Department of Agriculture is soliciting comments on the draft Environmental Assessment for the release of the golden miconia butterfly. Comments are accepted through May 26, 2020. HDOA press release
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, “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.
This article was originally published in the Maui News on July 8th, 2018, as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.
Read more Kiaʻi Moku articles.