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In November 2018, Department of Land and Natural Resources, Division of Forestry and Wildlife (DLNR-DOFAW) staff discovered unknown caterpillars (larvae) defoliating māmaki in the back of Olowalu, in the West Maui Mountains. Within a week, the same caterpillars were found feeding on māmaki plants in East Maui.
Specialists confirmed this new pest as the ramie moth, Arcte coerula (Guenée, 1852) (Lepidoptera: Noctuidae). This is the first detection of the ramie moth in Hawaiʻi and the United States. In November 2020, this new pest had spread to Hawaiʻi Island and most recently in 2024, the ramie moth was also detected on Oʻahu.
The ramie moth poses threats to many of Hawaiʻi's endemic species. Caterpillars cause huge defoliation of māmaki leaves which can lead to the eventual death of infested plants. This impacts our native forests where māmaki is an important ecological component of mesic forests. The ramie moth also feeds on other related nettle species and competes for the same resources as our endemic insects such as the Kamehameha Butterfly which also specializes on māmaki and other endemic nettles.
Māmaki is also an important plant for all of us! It is used commonly in lāʻau lapaʻau practices and has become an emerging agricultural tea crop for the islands due to the plant's medicinal properties.
Māmaki is important ecologically, culturally, and agriculturally and we are taking efforts to combat this new invasive in Hawaiʻi.
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Ramie moth eggs are clear-white in color, circular in shape and approximately 1mm in diameter. They are mostly found individually on the underside of leaves, along the leaf edge or veins. It takes less than a week for eggs to hatch once laid.
In some instances, multiple eggs may be laid on a single leaf. In general, females will lay an average of five to ten eggs per plant. However, there are instances where we have found over 200 eggs on a single tree either scattered throughout the plant or laid in a large, dense egg mass as shown below on the right.
Early instar ramie caterpillars (left) are green and white in color with black markings on its sides, distinguishing them from other Lepidoptera that also use māmaki as a food source. See the identification section for comparisons between species.
Late instar ramie caterpillars (right) are most often black in color with distinctive red spots, yellow markings on its sides, and long white hairs. The caterpillars have no stinging properties and will not harm you if touched. See the morphs section below for information about ramie larvae variations. When disturbed, later instars will rear up their bodies, thrash around, and regurgitate green liquid in self-defense. See the behaviors section for more information and visual examples.
Ramie moth larvae pupate in the soil or at the base of the plant in leaf litter by silking the soil or plant material together in a protective casing.
Pupae are a dark brown-black color and are on average 28mm in length. There is some variation in pupal size.
Once pupated, ramie moths take about 13 to 25 days to emerge. Variation in emergence time is likely due to seasonal temperature and rainfall changes.
Adult emerging from pupal casing in the soil
Adults are large moths, with a wingspan ranging from 65mm to 90mm and a body length of 28mm to 32mm long from the head to the tip of the abdomen.
The ramie moth's forewings are dark brown with black markings, silvery-blue speckles, and scalloped edges. Their hind wings also have distinctive, bright, silvery-blue markings. Typically the adults will hold its wings back when resting.
Adults are nocturnal and feed on tree sap or rotting/overripe fruit.
Wild adult resting on a māmaki leaf
Black Morphs: Under crowded conditions, the black bands on the caterpillar's bodies widen and the larvae become mostly black in color. Most larvae collected in Hawaiʻi are black morphs indicating that there is likely more than one caterpillar in the area.
Yellow Morphs: Under solitary conditions, the black bands on the caterpillar's bodies narrow and the larvae become mostly yellow in color. During the off season, the yellow morph will be more abundant as the population declines into the summer and fall months.
The Kamehameha Butterfly (Vanessa tameamea), a species endemic to the Hawaiian islands also feeds on māmaki and other endemic nettles (Urticaceae). This species also has morph variations that should not be confused with the ramie moth.
Green Morphs: Caterpillars are a lighter green color in warmer, sunnier locations. More common across the islands.
Brown Morphs: Caterpillars are a darker brown-purple color in cooler locations. Observed on Hawaiʻi Island, Maui Nui, and Kauaʻi.
Image courtesy of DLNR-DOFAW
There are four common caterpillars you will find on māmaki, two native and two invasive to the Hawaiian Islands.
At early stages, these caterpillars are all green in color with very little patterning, making them very difficult to differentiate.
Here are a few tips and tricks that will help you identify the caterpillars on your māmaki.
First instar ramie moth larvae emerge at about 2mm in length and grow rapidly through five instars, up to 100mm before pupating.
Early Instar Characteristics:
Late Instar Characteristics:
Feeding Damage
As early instars, the ramie moth larvae move around the māmaki plant creating small holes in the middle of leaves (left).
In later larval stages, the caterpillars create sizable holes through feeding damage and completely strip the leaves, leaving only the major leaf veins (right).
Image courtesy of DLNR-DOFAW.
Kamehameha butterfly larvae are the closest in size to the ramie moth caterpillars ranging from 2mm to 45mm in length.
Early instar characteristics:
Late instar characteristics:
Young larvae always feed inward from the leaf margins by clipping the leaves.
They also create a tent-like structure for protection using the edge of a leaf.
Udea stellata larvae are much smaller than the other species that feed on māmaki ranging from 1mm to 25mm in length and undergoes 6 larval instars before pupating.
Caterpillars mainly feed on the underside of leaves creating a web like structure between leaf veins for protection.
The web-like structure is surrounded by brown patchy spots from the feeding damage that occurs outside its protective home.
Green garden looper larvae feed on a wide variety of plant species and range from 1mm to 40mm in length.
Green garden looper larvae feed on plants in a variety of families, many of them being vegetable crops.
Early larval stages do not eat all the way though the leaves leaving brown spots. Later stages make holes throughout the leaves, and can defoliate plants with large infestations.
Ramie moths are very distinct from other caterpillar species that feed on māmaki because of the aggressive defensive behavior the larvae exhibit.
Early instar larvae defensively drop from leaves when disturbed and move quickly between the plants.
Later instars will not flee but become more defensive, rearing up its head, thrashing around, and regurgitating a green liquid to deter predators as demonstrated below.
Ramie moth has been detected on Maui, Hawaiʻi Island, and Oʻahu. Larvae have been recorded in residential, agricultural, and native forests. Further surveys will be conducted by the University of Hawaiʻi to identify additional locations where this pest may be found. See the interactive map below for the current recorded locations of reported ramie moths in Hawaiʻi.
Worldwide, ramie moths can be found in Asia, Oceania, Australia, Fiji, and Papua New Guinea.
Field surveys have shown that ramie moths have multiple generations per year.
Populations increase in the winter around January, peak in the spring, from February to April, and decrease dramatically in the summer and fall.
Low-density populations of the ramie moths can be found throughout the year in Hawaiʻi.
Larvae are known to feed on a range of host plants in the nettle family (Urticaceae).
Adults do not cause any damage to plants and will feed on rotting/decaying fruits.
In Hawaiʻi, we have found that the caterpillars feed and complete development on the 4 nettles below:
There is very little information available on how to manage this pest. In Australia, botanical insecticides (such as neem, derris powder, pyrethrum), insecticidal soaps, and microbial products such as spinosad and Bacillus thuringiensis kurstaki have been used. Management information used in Australia can be found here.
However, these products are not labeled for use in Hawaiʻi on māmaki plants and are not recommended in Hawaiʻi as they will also impact the endemic Lepidoptera populations that feed on māmaki and our other endemic Urticaceae.
Currently, the best management strategy is continual monitoring of your plants and the removal of eggs and larvae when found. Eggs are usually clustered around a few trees so search nearby plants if eggs have been detected. If large amounts of feeding damage is observed on your māmaki trees, check the area for caterpillars. Early instar larvae move quickly throughout the plant and can drop to the group and spread to neighboring areas. Monitoring should be done year around but we have noticed caterpillars are most abundant from December through May.
Do not move plant material between islands and different locations especially to areas where the ramie moth has not been detected.
Biological control is currently being explored as a management strategy. Below are all the parasitoids, predators, and pathogens that have been observed attacking ramie moth eggs and larvae in the field:
Parasitoids
Predators
Pathogens
Please report all sightings to 643pest.org or email ipmlab@hawaii.edu with the following information:
Please collect all eggs and caterpillars alive for research purposes. It is best to store them in a container with some holes and leaves until we can collect the specimens from you. If you need collection boxes please contact us.
If you find ramie eggs or caterpillars or have any questions, please contact Michelle Au at:
Insect Ecology and Integrated Pest Management Laboratory
Email: ipmlab@hawaii.edu
Michelle Au
Plant and Environmental Protection Sciences
College of Tropical Agriculture and Human Resilience
University of Hawaiʻi at Mānoa
For more information see publication here.
If you require information in an alternative format, please contact us at: ctahrADA@hawaii.edu.
Website created by Erin Patterson