Mamaki

New Pest of Māmaki638053586010112253

DESCRIPTION OF RAMIE MOTH

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 the first detection of the ramie moth in Hawaiʻi and the United States. As of November 2020, this new pest has spread to Hawaiʻi Island.

The ramie moth poses threats to several 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 competes for the same resources as the endemic Kamehameha Butterfly which also specializes in māmaki and other endemic nettles.

Māmaki is also an important plant for all of us! It is used commonly in lāʻau lapaʻau healing practices and has become an emerging agricultural industry for the islands due to the plantʻs medicinal properties.

Māmaki is an important ecologically, culturally, and agriculturally and we are taking efforts to combat this new invasive in Hawaiʻi.

We aim to provide information that will help you identify ramie moth larvae, the damage caused to māmaki plants, differentiating it from our endemic insects on māmaki, and methods for management.

Māmaki_plant638053617902456497

Life Stages:

EGGS:

Ramie eggs are clear-white in color, circular in shape at approximately 1 mm in diameter, and laid singly on the underside of leaves.

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, we have found over 200 eggs on a single tree. Eggs can be found scattered throughout the plant or laid in an egg mass shown below. It takes less than a week for eggs to hatch.

Egg mass. Wood Valley Farms 11 29 2021 2 resized638011270473058534

egg 1x 2638054474625491511

LARVAE:

Ramie caterpillars are often mistaken for culturally important endemic insects such as Hawaiʻi's state insect the Kamehameha butterfly (Vanessa tameamea), or the endemic moth Udea stellata, caterpillars because of their preference for the same host plants.

Early instar ramie larvae 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 below for comparisons.

PUPAE:

Larvae pupate in the soil or at the base of the plant in leaf litter.

Pupae are an average of 28 mm in length and take about 13 to 25 days to emerge. Variation in emergence time is likely due to seasonal temperature changes.

IMG_7683 copy

ADULTS:

Large moths (28-32 mm from head to the tip of the abdomen and 65-90 mm wingspan) with a dark brown head, and dark brown forewings with black markings, speckles of silvery-blue, and scalloped wing edges. Hindwings have distinctive bright silvery-bluish markings.

Adults are nocturnal and feed on tree sap or rotting/overripe fruit.

BIOLOGY:

Field surveys on Maui and Hawaiʻi Island have shown the ramie moth to have multiple generations per year.

Populations peak in the spring, from March to May, and decrease dramatically in the summer.

Low-density populations of the ramie moth can be found throughout the year in Hawaiʻi.

caterpillar w. scalebar resized1

BEHAVIOR:

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 were observed defensively dropping from leaves when disturbed and moving quickly between leaves on the plant.

As later instars, the larva will rear up its head, thrash around, and regurgitate a green liquid to defend itself.

IDENTIFYING CATERPILLARS ON MĀMAKI

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 identify.

Here are a few tips and tricks that will help you identify the caterpillars on your māmaki.

Ramie Moth (Arcte coerula) Invasive

caterpillar w. scalebar resized2638012145663832423

First instar ramie moth larvae emerge at about 2 mm in length and grow rapidly through five instars, up to 100 mm before pupating.

Early instar caterpillar characteristics:

Moves in an inching motion
Green and white coloration
Tan head capsule
Head capsule will turn black as it grows
Black dots on side of its body
4 sets of back legs (prolegs) near the end of its body
Very active
Inches away when disturbed

Late instar caterpillar characteristics:

Vibrant yellow and black
Orange-red spots on their sides
Thin white hairs
Black/reddish-brown head capsule

Kamehameha Butterfly (Vanessa tameamea) Native

Image courtesy of DLNR-DOFAW.

Kamehameha butterfly larvae range from 2 mm to 45 mm in length.

Early instar caterpillar characteristics:

Moves in a crawling motion
Green and black coloration
Black head capsule
Back legs (prolegs) spaced evenly throughout its body
Not very active
Hides when disturbed

Late instar caterpillar characteristics:

Green or purplish-brown in color
Green band on its side
Thick, short spines on its body

Ramie moth color morphs:

YELLOW MORPH: Under solitary conditions, the black bands on the larva's body will narrow.

Hartinson w. scalebar

BLACK MORPH: The black bands widen under crowded conditions. Most larvae collected in Hawaiʻi are the black morph indicating that there is likely more than a single caterpillar in the area.

IMG_8743 w. scalebar

Kamehameha butterfly color morphs:

GREEN MORPH: Caterpillars are lighter in warmer, sunnier locations. More common across the islands.

Vanessa tameamea 5th instar larva green morph Kauai

Image courtesy of DLNR-DOFAW.

BROWN MORPH: Caterpillars are darker in cooler locations.

Vanessa tameamea 5th instar larva brown morph Kauai

Image courtesy of DLNR-DOFAW.

Ramie moth feeding characteristics:

As early instars, the ramie larvae move around the māmaki plant creating small holes in the middle of leaves.

In later larval stages, the ramie caterpillars create sizable holes through feeding damage and completely strip leaves, leaving only the major leaf veins.

Kamehameha butterfly feeding characteristics:

Young larvae always feed inward from the leaf margins, clipping leaves.

Vanessa tameamea large shelter

Image courtesy of DLNR-DOFAW

They also create a tent-like structure for protection using the edge of a leaf.

Vanessa tameamea shelter

Udea stellata Native

Udea stellata caterpillars are much smaller in size undergoing 6 larval instars before pupating.

Caterpillars mainly feed on the underside of leaves creating a web like structure between leaf veins. Late instar U. stellata is roughly the same length as an early instar ramie moth larvae.

Udea stellata late instar caterpillar characteristics:

Moves in a crawling motion
Green and white coloration
Green head capsule with 4 black dots on the top
Back legs (prolegs) spaced evenly throughout its body
Creates a web-like structure for protection surrounded by brown spots from feeding damage (shown below)
Not very active
Hides when disturbed

Udea Stellata feeding damage

Green Garden Looper (Chrysodeixis eriosoma) Invasive

Tomato Looper

Late instar larvae of the green garden looper.

This 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. Later stages make holes throughout the leaves, and can defoliate plants with large infestations.

Tomato looper early & late instar caterpillar characteristics

Moves in an looping motion
Green and white coloration
Green head capsule with a black line across the side of its face (see arrow)
Black dots on the side and throughout its body
2 sets of back legs (prolegs) near the end of the abdomen
Feeding damage creates holes throughout leaves

MĀMAKI DAMAGE

Ramie larvae will feed on both young and mature leaves of host plants. It is difficult to identify the culprit of your māmaki damage based on feeding alone.

The Kamehemahea butterfly and Udea stellata will not cause huge amounts of feeding damage.

Both endemic caterpillars will feed in or near their protective structures. See above "Identifying Caterpillars on Māmaki" for comparisons.

WoodValley Farm638012181746090602

Image courtesy of Wood Valley Farms

HOSTS:

Larvae are known to feed on a range of host plants in the nettle family (Urticaceae).

This includes but is not limited to: Cypholophus spp., Debregeasia spp., Girardinia spp., Pipturus spp., and especially Boehmeria spp. Other sources noted larvae feeding on Vitis sp. (Vitaceae) and Trema tomentosa (Cannabaceae).

Adults do not cause any damage to plants.
.

DISTRIBUTION

Ramie moth has been detected on Maui and Hawaiʻi Island. Larvae have been recorded in both residential areas and native forests. Further surveying will be conducted by the University of Hawaiʻi to identify additional locations where this pest may be found.

Worldwide, ramie moth can be found in Asia, Oceania, Australia, Fiji, and Papua New Guinea.

MANAGEMENT

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 other endemic Urticaceae.

Currently the best management strategy is continual monitoring of your plants and the removal or eggs and larvae when found. Eggs are usually clustered around a few plants so search near-by plants if eggs have been detected. If large amounts of feeding damage is observed on your māmaki leaves, 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.

Please report all sightings to 643pest.org or ipmlab@hawaii.edu.

Currently, biological control is being explored as a management strategy. Field surveys have detected egg and larval parasitism on both Maui and Hawaiʻi Island. There may also be predation occurring from ants on eggs and early instars and birds such as chickens in later instars.

Screen Shot 2024-03-05 at 10.09.34 AM