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Puriri moth - Aenetus virescens

By N A Martin (2010)

Classification
Class:Insecta
Order:Lepidoptera
Family:Hepialidae
Scientific Name:Aenetus virescens (Doubleday, 1843)
Male puriri moth Aenetus virescens (Lepidoptera: Hepialidae) on a tree trunk (photograph by Ruud Kleinpaste, copyright Ruud Kleinpaste).
Male puriri moth Aenetus virescens (Lepidoptera: Hepialidae) on a tree trunk (photograph by Ruud Kleinpaste, copyright Ruud Kleinpaste).
Old puriri moth Aenetus virescens (Lepidoptera: Hepialidae) burrow and feeding scar in a Carpodetus serratus (putaputaweta) tree trunk. The feeding scar has grown new bark, but the caterpillar burrow is still open (photograph by Nicholas A. Martin, copyright Nicholas A. Martin).
Old puriri moth Aenetus virescens (Lepidoptera: Hepialidae) burrow and feeding scar in a Carpodetus serratus (putaputaweta) tree trunk. The feeding scar has grown new bark, but the caterpillar burrow is still open (photograph by Nicholas A. Martin, copyright Nicholas A. Martin).
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Synonyms


Hepialus virescens Doubleday, 1843
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Biostatus and Distribution

This endemic moth is found throughout the North Island of New Zealand.

Conservation status: The moth occurs in natural ecosystems and parkland where suitable trees and litter and dead branches occur. It can live in adventive and cultivated trees.

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Life Stages and Annual Cycle

Moths may emerge any month of the year, although the peak months are October to December, with a second minor peak in March. The female moth, the largest moth in New Zealand, has a wing span up to 150 mm; the male is smaller with a wing span of 100 mm. Moths mainly fly in the evening. Male moths are more likely to be seen at lights.

The moths are usually green, but the intensity of colour and wing patterning is very variable. The markings of the male's forewings are white and the hind wings are greener than those of the female. Colour variations from blue-green, yellow, red and albino have been recorded.

Eggs and litter phase caterpillars

After mating, the female moth scatters eggs over the forest floor. Up to 2000 eggs may be laid. The eggs are round and pale yellow when first laid, turning black a few days later. After 12-14 days, litter phase caterpillars hatch from the eggs. The litter phase caterpillars live on the underside of bracket fungi or fungal fruiting bodies encrusting twigs and branches. They make a tunnel and feed on the fungal fruiting body, and cover their feeding areas with web covered in frass (insect droppings). The fungus feeding stage lasts two to three months, during which the caterpillar may moult (change its skin).

Transfer phase caterpillars

At the end of the litter phase, it moults (changes its skin) to a darker transfer phase caterpillar. These caterpillars locate trees, which they climb, and bore through the bark into the wood of the trunk or branch. They form a distinctive seven-shaped tunnel. The top of the ‘seven’ follows the radius of the trunk/branch and slopes upwards. The longer part of the burrow descends vertically and is where the caterpillar rests. The opening of the burrow and the area used for feeding are covered with a protective web.

Tree phase caterpillars

The transfer phase caterpillar moults to a paler tree phase caterpillar. This caterpillar is a delicate transparent purplish-pink with a hardened dark-brown head capsule. It grazes on live callus tissue that develops round the opening of the burrow. Some frass is used in the web cover, but is ejected through a hole at the bottom of the web covering. As the caterpillar grows, it enlarges its burrow. It extends the radial burrow and makes a larger vertical burrow. The establishment burrow may become blocked with frass. The mature caterpillar can grow to about 100 mm long and 15 mm in diameter. The tree phase caterpillar can live up to five years, but this stage may be as short as eight months. The mean time for male caterpillars is about two years and for females, about three years.

Pupation and moth emergence

When the caterpillar has reached full size, it first removes pieces of the web covering the feeding scar. It may make many small holes or remove the entire central portion of the web. Then the caterpillar blocks the top of the vertical burrow with a fibrous disc and pupates.New pupae may be found in every month from March to November. Pupal duration is shortest for those formed in October and November, but the mean duration is 151 days for males and 173 days for females. When the moth is ready to emerge, the pupa wriggles up the shaft, pushes up the disc and protrudes through the camouflaging web. Movement up the shaft is helped by 12 horny ridges, armed with hooklets, on the upper side of the abdomen and five similar ridges on the underside. It is not known how male and female moths find each other before mating.

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Recognition

The moth’s large size and distinctive colouring makes it easily recognisable. The characteristic damage to trees also makes the presence of old feeding sites easy to recognise. Active feeding sites are less easy to detect because of the camouflaged webbing. The fungal-feeding, litter phase caterpillars are the most difficult stage to detect because potential sites are more difficult to find unless deliberately sought out and because the feeding sites are covered by webbing.

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Natural Enemies

Diagrams illustrating the position and form of diseased puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillars (Drawings by JR Grehan and PJ Wrigley, published in New Zealand Entomologist, 1984, 8: 61-63, Figs 1-4).
Diagrams illustrating the position and form of diseased puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillars (Drawings by JR Grehan and PJ Wrigley, published in New Zealand Entomologist, 1984, 8: 61-63, Figs 1-4).

Predators

Moreporks (ruru, small owls) and native bats are reported to catch flying moths. Possums and cats will also eat moths. Kaka tear at wood to try to reach caterpillars in tree branches. No parasitoids are known.

Pathogens

An unnamed bacterium has been found killing puriri moth caterpillars. Three fungi have been found in caterpillars and pupae. Beauveria bassiana kills the caterpillars and forms a mass of fluffy white fruiting body extending over the larval feeding area. One unnamed fungal disease kills larvae and pupae, while another unnamed species kills pupae and forms distinctive forms finger-like coremia that protrude out of the tunnel.

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Host Plants

The newly hatched (neonate) caterpillars live on fungi. Larger caterpillars live in the trunk and branches of a wide variety of trees and shrubs. Host plants include native, naturalised, and cultivated species.

The caterpillar damages the tree by making radial and vertical burrows in live wood, in which the body of the caterpillar rests. At the entrance to the burrow, they graze on the cambium, forming a diamond-shaped feeding scar. They cover the scar and burrow with a tough web that is coloured like the bark of the tree. After the moth has left the pupa, the hole may grow over or remain open. The vertical burrows remain after the caterpillar has left and the defect reduces the usefulness of the wood as a timber. Heavy infestations can weaken the tree, especially those with thin trunks.

Caterpillars can also infest non-host trees, such as cherry (Prunus) and Eucalyptus. In these cases,

Table: Host plants of puriri moth Aenetus virescens (Lepidoptera: Hepialidae)from Plant-SyNZ database (March 2010). The reliability score shows the quality of evidence for the host association (10=high).
Vernacular NameScientific NameFamilyReliabilityBiostatus
Blackwood, Tasmanian blackwood Acacia melanoxylon R. Br.Mimosaceae8naturalised
Wineberry, Mako, Makomako Aristotelia serrata (J.R.Forst. & G.Forst.) W.R.B.OliverElaeocarpaceae10endemic
Buddleia, Butterfly bush, Summer lilac Buddleja davidii Franch.Buddlejaceae10naturalised
Marble leaf, Motorbike tree, Kaiwētā, Piripiriwhata, Punawētā, Putaputawētā, Putawētā Carpodetus serratus J.R. et G. Forst.Grossulariaceae10endemic
Beefwood, She-oak Casuarina sp. Casuarinaceae7unknown
Kākawariki, kanono, Kapukiore, Karamū-kueo, Kueo (fruit), Manono, Pāpāuma, Raurēkau, Toherāoa Coprosma grandifolia Hook. f.Rubiaceae5endemic
Tree tutu, Pūhou, Tāweku, Tūpākihi, Tutu Coriaria arborea R. LindsayCoriariaceae5endemic
Bentham's cornel, Himalayan strawberry tree, Strawberry dogwood Cornus capitata Wall.Cornaceae10naturalised
Hawthorn, Neapolitan medlar, White hawthorn Crataegus monogyna Jacq.Rosaceae10naturalised
Cedar of Goa, Mexican cypress, Portuguese cypress Cupressus lusitanica Mill.Cupressaceae8naturalised
Red escallonia Escallonia rubra (Ruiz & Pav.) Pers.Grossulariaceae5cultivated
Brown barrel, Cut tail Eucalyptus fastigata H.Deane & MaidenMyrtaceae6naturalised
Giant gum, Mountain ash, Stringy gum, Swamp gum Eucalyptus regnans F. Muell.Myrtaceae8naturalised
Sydney blue gum Eucalyptus saligna Sm.Myrtaceae10naturalised
Common beech, European beech Fagus sylvatica L.Fagaceae10cultivated
Ash, Common ash, European ash Fraxinus excelsior L.Oleaceae10naturalised
Broadleaf, Huariki (fruit), Kāpuka, Māihīhi, Pāpāuma, Paraparauma, Tapatapauma Griselinia littoralis RaoulCornaceae10endemic
, Akakōpuka, Akapuka, Puka, Pukatea Griselinia lucida G.Forst.Cornaceae10endemic
Lacebark, Hohere, Hoihere, Houhere, Houhi, Houhi ongaonga, Houī, Ongaonga, Whauahi, Wheuhi Hoheria populnea A. CunninghamMalvaceae10endemic
Graceful lacebark, Lacebark, Houhere, Houhiongaonga Hoheria sexstylosa ColensoMalvaceae10endemic
Black walnut, California walnut Juglans nigra L.Juglandaceae10cultivated
White tea tree, Kānuka, Kōpuka, Manuea, Mānuka, Mānuka-rauriki, Mārū, Rauiri, Rauwiri Kunzea ericoides (A. Rich.) J. Thompson.Myrtaceae10non-endemic
Red tea tree, Tea tree, Kahikātoa, Kātoa, Mānuka, Pata, Rauiri, Rauwiri Leptospermum scoparium J.R. et G. Forst.Myrtaceae10non-endemic
Tall mingimingi, Hukihukiraho, Kaikaiatua, Mānuka-rauriki, Mikimiki, Mingi, Mingimingi, Ngohungohu, Tūmingi Leucopogon fasciculatus (Forst. f.) A. Rich.Epacridaceae10endemic
Broadleaf privet, Tree privet Ligustrum lucidum W.T.AitonOleaceae10naturalised
Chinese privet, Small-leaf privet Ligustrum sinense Lour.Oleaceae10naturalised
Apple, Crab-apple Malus x domestica Borkh.Rosaceae10naturalised
Ngaio Myoporum laetum Forst. f.Myoporaceae10endemic
Coastal maire, Maire Nestegis apetala (Vahl) L.A.S.JohnsonOleaceae10non-endemic
Black maire, Maire, Maire raunui, Pau Nestegis cunninghamii (Hook.f.) L.A.S.JohnsonOleaceae10endemic
White maire, Maire, Maire raunui, Maire rauriki Nestegis lanceolata (Hook.f.) L.A.S.JohnsonOleaceae10endemic
Narrow-leaved maire, Maire kōtae, Maire rauriki, Maire roro, Maire rōroro, Rōroro Nestegis montana (Hook.f.) L.A.S.JohnsonOleaceae10endemic
Red beech, Hutu, Hututawai, Raunui, Tawai, Tawhai Nothofagus fusca (Hook. f.) Oerst.Nothofagaceae10endemic
Silver beech, Tawai, Tawhai Nothofagus menziesii (Hook. f.) OerstedNothofagaceae10endemic
Black beech, Tawhai rauriki Nothofagus solandri (Hook. f.) Oerst.Nothofagaceae10endemic
Hard beech, Hutu, Hututawai, Tawhai raunui Nothofagus truncata (Colenso) CockayneNothofagaceae10endemic
Olive Olea europaea L.Oleaceae10naturalised
Akewharangi, Heketara, Ngungu, Taraheke, Tātaraheke, Wharangi-piro Olearia rani (A. Cunn.) DruceAsteraceae5endemic
 Paulownia elongata Scrophulariaceae10cultivated
Ahikōmau, Hine-kaikōmako, Kahikōmako, Kaikōmako Pennantia corymbosa J.R.Forst. & G.Forst.Icacinaceae5endemic
New Zealand hazel, Nonokia, Nonorangi, Tainui Pomaderris apetala Labill.Rhamnaceae10non-endemic
Alpine pepper tree, Mountain horopito, Pepper tree, Red horopito, Horopito, ōramarama, Ramarama Pseudowintera colorata (Raoul) DandyWinteraceae10endemic
Common oak, English oak, Oak, Truffle oak Quercus robur L.Fagaceae10naturalised
Red oak Quercus rubra L.Fagaceae10naturalised
Westland quintinia Quintinia acutifolia KirkGrossulariaceae5endemic
Quintinia, Kūmarahou, Tāwheowheo Quintinia serrata A. Cunn.Grossulariaceae10endemic
 Raukaua simplex (G.Forst.) A.D.Mitch., Frodin & HeadsAraliaceae10endemic
Evergreen buckthorn, Italian buckthorn Rhamnus alaternus L.Rhamnaceae10naturalised
 Ulmus procera Salisb.Ulmaceae10cultivated
New Zealand oak, Kauere, Pūriri Vitex lucens KirkVerbenaceae10endemic
Kāmahi, Tawhero, Tōwai Weinmannia racemosa L. f.Cunoniaceae5endemic
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Control

Puriri moths are part of the biodiversity of native ecosystems. Where host trees grow in native ecosystems, the moth should be accepted. There are, however, some circumstances where control could be justified.

For single specimen trees, puriri moth caterpillars can be killed by injecting insecticide into their burrows.

In orchards and tree collections, the risk of infestations can be reduced by keeping the ground clean of any dead wood on which fungi can grow and develop. This prevents the young fungal-feeding litter phase caterpillars from establishing.

For information about reducing risk to forest trees go to www.nzffa.org.nz/images/design/Pests/Puriri-moth/Puriri-moth.html

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Additional Information

Behaviour of moths

It is not known how male and female moths find each other for mating. The male moth has brush organs on the tibia of the hind leg. Other moths of the family Hepialidae that have brush organs show courtship; the males fly in groups at dusk and the females fly to them for copulation. It is believed that the males emit a pheromone that attracts the female moths. Mating has not been observed for puriri moths, but probably occurs after dark.

Sometimes many male moths gather at lights at night. Is emergence of moths synchronised and if so how?

Insects associated with pupal skins

When a moth leaves its pupal skin, it excretes all the waste that has accumulated during the pupal stage. An intact pupal skin with brown waste liquid present had hover fly larvae living in it. Several kinds of hover fly have larvae that live in wet decaying matter. The adult female fly was probably attracted to the smell of the waste liquid.

Insects associated with empty tree burrows

Other insects and spiders colonise the vacated puriri moth burrows. Some insects such as weta are reported to stop the tree growing over the hole by chewing the edge of the opening. Māori knew that weta inhabited puriri moth burrows and named Carpodetus serratus putaputaweta, because it often had many weta living in it.

Impact on North Island beech forests

In the North Island, puriri moths cause damage to beech trees. The damage to the wood lowers the value of beech as a timber tree in the North Island and makes it less valuable to fell. Through its damage to the timber, did puriri moth save many North Island beech forests from clear felling?

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Information Sources

Dugdale JS 1994. Hepialidae (Insecta: Lepidoptera). Fauna of New Zealand 30: 1-164.

Early J 2009. Know your New Zealand insects & spiders. Northcote, Auckland, New Zealand, New Holland Publishers (NZ) Ltd. 176 p.

Grehan JR 1987a. Life cycle of the wood-borer Aenetus virescens (Lepidoptera: Hepialidae). New Zealand Journal of Zoology 14: 209-217.

Grehan JR 1987b. Evolution of arboreal tunnelling by larvae of Aenetus (Lepidoptera: Hepialidae). New Zealand Journal of Zoology 14: 441-462.

Grehan JR 1988. Fungal and vascular plant polysaccharide digestion by larvae of Aenetus virescens (Lepidoptera: Hepialidae). New Zealand Entomologist 11: 57-67.

Grehan JR, Wigley PJ 1984. Fungal and bacterial diseases of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), larvae. New Zealand Entomologist 8: 61-63.

www.nzffa.org.nz/images/design/Pests/Puriri-moth/Puriri-moth.html (describes impact on wood quality).

www.nzffa.org.nz/images/design/Pests/Puriri-moth/Puriri-MothFHnews162.html, (early reports of puriri moth damage to trees)

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Acknowledgements

John Grehan for photographs and illustrations.

John Bain for providing the photographs from Scion

Robert Hoare for photographs of moths and information.

Ruud Kleinpaste for a photograph of a moth.

Eric Scott for helpful suggestions.

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

Landcare Research New Zealand Limited (Landcare Research) for permission to use photographs.

New Zealand Forest Research Institute Limited (Scion) for permission to use photographs.

Landcare Research       Plant and Food