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Mamaki under attack: Ramie moth confirmed on Big Island

Another Big Island crop is under attack by an invasive species prompting the Department of Agriculture to issue a pest alert.

The Ramie moth, which is a new pest of mamaki plants and their relatives, has made its way to the Big Island’s native forests and plants at residences, the state Department of Agriculture Plant Pest Control Branch confirmed last week. The pest was previously detected on Maui in late 2018.

Mamaki (Pipturus albidus), is a member of the nettle family, endemic to and currently only growing in the Hawaiian islands. Although commonly found wild, commercial crops are grown to satisfy a growing demand for the plant that is made into a tea known for its traditional medicinal qualities.

The Ramie moth (Arcte coerula) was first detected in late November 2020 on the eastern side of the Big Island, said Janis Matsunaga, entomologist with the state Department of Agriculture. In February, a “new pest advisory” was posted by the department.

“On the Big Island, we have not yet received reports of large infestations, which warranted control, just reports of one or two larvae at a location,” she said.

Ramie moths are native to Southeast Asia, and have been spread by people to the Philippines, Japan, Australia, New Zealand, and now two islands in the Aloha State. It feeds on a range of host plants in the nettle (Urticaceae) family, including Cypholophus, Debregeasia, Girardinia, Pipturus, and especially Boehmeria.

In Hawaii, the Ramie moth has only been reported in mamaki thus far, but other native species in the nettle family include Boehmeria grandis (ʻakolea), Hesperocnide sandwicensis, Neraudia sericea, Pilea peploides, Touchardia latifolia (olona), and Urera glabra (opuhe).

Though this invasive moth can spread with the wind, it is not yet known how it was brought to Maui and the Big Island. The moth can also spread when people move or import plants in which the moth has laid eggs. The eggs are clear-white in color and circular in shape (about 1 mm in diameter), and laid singly on the underside of leaves.

From those eggs, young larvae (caterpillars) emerge, eating small holes in the leaves and progressively stripping the leaves until only the veins remain. In addition to damaging plants grown for agriculture and Native Hawaiian cultural practices, the moth threatens the endemic Kamehameha butterfly (Vanessa tameamea) by competing for the same native host plant resources and damaging endemic plants that make up native forests.

Ramie caterpillars are black and sometimes yellow, with bright orange-red spots and white hairs and measure about an inch in length. An adult Ramie moth has a wingspan up to 3.5 inches. Kamehameha butterfly larvae are black when first hatched, and greenish when ready to make a cocoon. They typically grow to a wingspan of 3 inches.

Matsunaga said researchers at the University of Hawaii are searching for natural enemies in the field, which may be impacting Ramie moth populations, however, research is still in the early stages.

If there is a suspected Ramie moth present on a grower’s plant the most efficient and quickest way to get a confirmation is to take as many clear images as possible and confirm the plant which you see the larvae feeding on. Matsunaga encourages making a pest report at 643pest.org or via the 643-Pest app on a smartphone. Those without internet access can call (808) 643-PEST.

Though the larvae will chew holes in the mamaki leaves, they are still safe for consumption, said Matsunaga. As with other fruits and vegetables, people should take similar precautions by washing any plant material before consumption.

The Department of Agriculture advises people not to move host plants, such as mamaki, between areas on the island or to other islands.

“Even though there are no formal plans to ban the transport of these plants interisland, all plants moving interisland should always be inspected by the Hawaii Department of Agricultureʻs Plant Quarantine Branch,” said Matsunaga.

View the “new pest advisory” at https://hdoa.hawaii.gov/pi/files/2021/03/NPA-21-01-Arcte-coerula-ramie-moth-reduced.pdf.
Source: Hawaii Tribune Herald

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