Puriri moth - Aenetus virescens
By N A Martin (2010)
|Scientific Name:||Aenetus virescens (Doubleday, 1843)|
Male puriri moth Aenetus virescens (Lepidoptera: Hepialidae) on a tree trunk (photograph by Ruud Kleinpaste, copyright Ruud Kleinpaste).
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.
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.
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.
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).
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.
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.
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,
|Vernacular Name||Scientific Name||Family||Reliability||Biostatus|
|Blackwood, Tasmanian blackwood||Acacia melanoxylon R. Br.||Mimosaceae||8||naturalised|
|Wineberry, Mako, Makomako||Aristotelia serrata (J.R.Forst. & G.Forst.) W.R.B.Oliver||Elaeocarpaceae||10||endemic|
|Buddleia, Butterfly bush, Summer lilac||Buddleja davidii Franch.||Buddlejaceae||10||naturalised|
|Marble leaf, Motorbike tree, Kaiwētā, Piripiriwhata, Punawētā, Putaputawētā, Putawētā||Carpodetus serratus J.R. et G. Forst.||Grossulariaceae||10||endemic|
|Beefwood, She-oak||Casuarina sp.||Casuarinaceae||7||unknown|
|Kākawariki, kanono, Kapukiore, Karamū-kueo, Kueo (fruit), Manono, Pāpāuma, Raurēkau, Toherāoa||Coprosma grandifolia Hook. f.||Rubiaceae||5||endemic|
|Tree tutu, Pūhou, Tāweku, Tūpākihi, Tutu||Coriaria arborea R. Lindsay||Coriariaceae||5||endemic|
|Bentham's cornel, Himalayan strawberry tree, Strawberry dogwood||Cornus capitata Wall.||Cornaceae||10||naturalised|
|Hawthorn, Neapolitan medlar, White hawthorn||Crataegus monogyna Jacq.||Rosaceae||10||naturalised|
|Cedar of Goa, Mexican cypress, Portuguese cypress||Cupressus lusitanica Mill.||Cupressaceae||8||naturalised|
|Red escallonia||Escallonia rubra (Ruiz & Pav.) Pers.||Grossulariaceae||5||cultivated|
|Brown barrel, Cut tail||Eucalyptus fastigata H.Deane & Maiden||Myrtaceae||6||naturalised|
|Giant gum, Mountain ash, Stringy gum, Swamp gum||Eucalyptus regnans F. Muell.||Myrtaceae||8||naturalised|
|Sydney blue gum||Eucalyptus saligna Sm.||Myrtaceae||10||naturalised|
|Common beech, European beech||Fagus sylvatica L.||Fagaceae||10||cultivated|
|Ash, Common ash, European ash||Fraxinus excelsior L.||Oleaceae||10||naturalised|
|Broadleaf, Huariki (fruit), Kāpuka, Māihīhi, Pāpāuma, Paraparauma, Tapatapauma||Griselinia littoralis Raoul||Cornaceae||10||endemic|
|, Akakōpuka, Akapuka, Puka, Pukatea||Griselinia lucida G.Forst.||Cornaceae||10||endemic|
|Lacebark, Hohere, Hoihere, Houhere, Houhi, Houhi ongaonga, Houī, Ongaonga, Whauahi, Wheuhi||Hoheria populnea A. Cunningham||Malvaceae||10||endemic|
|Graceful lacebark, Lacebark, Houhere, Houhiongaonga||Hoheria sexstylosa Colenso||Malvaceae||10||endemic|
|Black walnut, California walnut||Juglans nigra L.||Juglandaceae||10||cultivated|
|White tea tree, Kānuka, Kōpuka, Manuea, Mānuka, Mānuka-rauriki, Mārū, Rauiri, Rauwiri||Kunzea ericoides (A. Rich.) J. Thompson.||Myrtaceae||10||non-endemic|
|Red tea tree, Tea tree, Kahikātoa, Kātoa, Mānuka, Pata, Rauiri, Rauwiri||Leptospermum scoparium J.R. et G. Forst.||Myrtaceae||10||non-endemic|
|Tall mingimingi, Hukihukiraho, Kaikaiatua, Mānuka-rauriki, Mikimiki, Mingi, Mingimingi, Ngohungohu, Tūmingi||Leucopogon fasciculatus (Forst. f.) A. Rich.||Epacridaceae||10||endemic|
|Broadleaf privet, Tree privet||Ligustrum lucidum W.T.Aiton||Oleaceae||10||naturalised|
|Chinese privet, Small-leaf privet||Ligustrum sinense Lour.||Oleaceae||10||naturalised|
|Apple, Crab-apple||Malus x domestica Borkh.||Rosaceae||10||naturalised|
|Ngaio||Myoporum laetum Forst. f.||Myoporaceae||10||endemic|
|Coastal maire, Maire||Nestegis apetala (Vahl) L.A.S.Johnson||Oleaceae||10||non-endemic|
|Black maire, Maire, Maire raunui, Pau||Nestegis cunninghamii (Hook.f.) L.A.S.Johnson||Oleaceae||10||endemic|
|White maire, Maire, Maire raunui, Maire rauriki||Nestegis lanceolata (Hook.f.) L.A.S.Johnson||Oleaceae||10||endemic|
|Narrow-leaved maire, Maire kōtae, Maire rauriki, Maire roro, Maire rōroro, Rōroro||Nestegis montana (Hook.f.) L.A.S.Johnson||Oleaceae||10||endemic|
|Red beech, Hutu, Hututawai, Raunui, Tawai, Tawhai||Nothofagus fusca (Hook. f.) Oerst.||Nothofagaceae||10||endemic|
|Silver beech, Tawai, Tawhai||Nothofagus menziesii (Hook. f.) Oersted||Nothofagaceae||10||endemic|
|Black beech, Tawhai rauriki||Nothofagus solandri (Hook. f.) Oerst.||Nothofagaceae||10||endemic|
|Hard beech, Hutu, Hututawai, Tawhai raunui||Nothofagus truncata (Colenso) Cockayne||Nothofagaceae||10||endemic|
|Olive||Olea europaea L.||Oleaceae||10||naturalised|
|Akewharangi, Heketara, Ngungu, Taraheke, Tātaraheke, Wharangi-piro||Olearia rani (A. Cunn.) Druce||Asteraceae||5||endemic|
|Ahikōmau, Hine-kaikōmako, Kahikōmako, Kaikōmako||Pennantia corymbosa J.R.Forst. & G.Forst.||Icacinaceae||5||endemic|
|New Zealand hazel, Nonokia, Nonorangi, Tainui||Pomaderris apetala Labill.||Rhamnaceae||10||non-endemic|
|Alpine pepper tree, Mountain horopito, Pepper tree, Red horopito, Horopito, ōramarama, Ramarama||Pseudowintera colorata (Raoul) Dandy||Winteraceae||10||endemic|
|Common oak, English oak, Oak, Truffle oak||Quercus robur L.||Fagaceae||10||naturalised|
|Red oak||Quercus rubra L.||Fagaceae||10||naturalised|
|Westland quintinia||Quintinia acutifolia Kirk||Grossulariaceae||5||endemic|
|Quintinia, Kūmarahou, Tāwheowheo||Quintinia serrata A. Cunn.||Grossulariaceae||10||endemic|
|Raukaua simplex (G.Forst.) A.D.Mitch., Frodin & Heads||Araliaceae||10||endemic|
|Evergreen buckthorn, Italian buckthorn||Rhamnus alaternus L.||Rhamnaceae||10||naturalised|
|Ulmus procera Salisb.||Ulmaceae||10||cultivated|
|New Zealand oak, Kauere, Pūriri||Vitex lucens Kirk||Verbenaceae||10||endemic|
|Kāmahi, Tawhero, Tōwai||Weinmannia racemosa L. f.||Cunoniaceae||5||endemic|
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
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?
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)
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.
Last revised: 26 July 2010