INTERESTING INSECTS

By N A Martin (2010, revised 2018)

Puriri moth

Hepialus virescens Doubleday, 1843

This endemic moth is found throughout the North Island of New Zealand. It occurs in habitats with dead wood with suitable fungi for its young caterpillars and living host trees in which the larger caterpillars live in tunnels and graze callous tissue.

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. See a 2017 paper in The Weta by Graham and Care for photographs of some of the variable wing patterns and colours.

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.

Pinned specimens of female (top) and male (bottom) puriri moths Aenetus virescens (Lepidoptera: Hepialidae) showing the relative size of the two sexes. Creator: FRI photographers. © Scion. [Image: 3CP]

Female puriri moth, Aenetus virescens (Lepidoptera: Hepialidae) Creator: Birgit E Rhode. © Landcare Research. [Image: 3CN]

Yellow female puriri moths, Aenetus virescens (Lepidoptera: Hepialidae), top view. Creator: DSIR photographers. © Landcare Research. [Image: 3D6]

Yellow female puriri moths, Aenetus virescens (Lepidoptera: Hepialidae), side view. Creator: DSIR photographers. © Landcare Research. [Image: 3D5]

A green male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Robert Hoare. © Robert Hoare. [Image: 3CL]

A green-blue male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Robert Hoare. © Robert Hoare. [Image: 3DI]

A yellow male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Robert Hoare. © Robert Hoare. [Image: 3DJ]

Drawings of sections through the fungal feeding tunnels of litter phase puriri moth caterpillar Aenetus virescens (Lepidoptera: Hepialidae). Top, simple feeding cover. Bottom, feeding surface cover extended as a cone-like protrusion. Coarse stippling, dead wood; fine stippling, fungal tissue. Creator: John R. Grehan. © Drawings published in New Zealand Journal of Zoology, 1987, 14: 441-462, Figure 2. [Image: 3CY]

Webbing of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), litter phase caterpillars covering feeding site on fungal fruiting body. Creator: John R. Grehan. © John R. Grehan. [Image: 3D2]

Tunnel opening of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), litter phase caterpillar; tunnel exposed by removing of webbing. Creator: John R. Grehan. © John R. Grehan. [Image: 3D1]

Puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), burrows; left, new establishment burrow, pale; right, dark mature burrow with its smaller establishment burrow. Creator: DSIR photographers. © Landcare Research. [Image: 3D4]

Drawings of longitudinal sections of larval puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), burrows in wood; left, in Aristotelia serrata; note that part of the feeding area is under the bark; right, in Carpodetus serratusshowing establishment burrow blocked by frass and the large burrow closed by pupal operculum. Creator: John R. Grehan. © Drawings published in New Zealand Journal of Zoology, 1987, 14: 441-462, Figures 3 and 4. [Image: 3CZ]

Drawing of the external view of entrance to a puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillar burrow in Nothofagus solandri, showing the position of the radial tunnel and cover. Solid line, external cover; dashed line, extent of feeding surface under the bark; dotted circle, radial tunnel. Creator: John R. Grehan. © Drawing published in New Zealand Journal of Zoology, 1987, 14: 441-462, Figure 9b. [Image: 3CW]

Drawing of transverse section of feeding chamber and radial tunnel of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), in Nothofagus solandri. Dotted circle, longitudinal tunnel; fine stippling, cover. Creator: John R. Grehan. © Drawing published in New Zealand Journal of Zoology, 1987, 14: 441-462, Figure 10a. [Image: 3CX]

Newly established puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillar burrow in Carpodetus serratus. The web cover has been folded down. Note the fragments of wood. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DF]

Puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), web covering feeding area on Carpodetus serratus (putaputaweta). Note the pile of wet faeces below the entrance to the tunnel. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DA]

Puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), feeding area after web cover removed on (Carpodetus serratus (putaputaweta). Note the pile of wet faeces below the entrance to the tunnel. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DE]

Caterpillar of puriri moth Aenetus virescens (Lepidoptera: Hepialidae), in a burrow in a stem of Carpodetus serratus (putaputaweta). Length of the tunnel is 120 mm; length of the caterpillar is 58 mm. Creator: FRI photographers. © Scion. [Image: 3CR]

Fully grown caterpillar of the puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), in a stem of Nothofagus menziesii (silver beech). Note the cap sealing the entrance to the vertical shaft. Creator: FRI photographers. © Scion. [Image: 3CQ]

Pupa of the puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), in a stem of Carpodetus serratus (putaputaweta). Length of this pupa is 55 mm. Creator: FRI photographers. © Scion. [Image: 3D0]

Empty pupal skin of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), dorsal (upper photo) and ventral (lower photo) views. Note the split skin through which the moth emerged. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3CV]

Pupal skin of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae): abdominal ridges that help the pupa to work its way out of its burrow. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3CU]

Pupal skin of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae); the tough, black head of the pupa has coarse ridges. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3CT]

Male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), just emerged from its pupa; note the empty pupal case protruding from the hole in the tree branch. Creator: John R. Grehan. © John R. Grehan. [Image: 3CM]

Male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), just emerged from its pupa and hanging to dry its wings. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 1IYG]

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.

Male puriri moth Aenetus virescens (Lepidoptera: Hepialidae) on a tree trunk. Creator: Ruud Kleinpaste. © Ruud Kleinpaste. [Image: 3CO]

Female puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Birgit E Rhode. © Landcare Research. [Image: 3CN]

A green male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Robert Hoare. © Robert Hoare. [Image: 3CL]

A green-blue male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Robert Hoare. © Robert Hoare. [Image: 3DI]

A yellow male puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). Creator: Robert Hoare. © Robert Hoare. [Image: 3DJ]

Puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), web covering feeding area on Carpodetus serratus (putaputaweta). Note the pile of wet faeces below the entrance to the tunnel. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DA]

Puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), feeding area after web cover removed on (Carpodetus serratus (putaputaweta). Note the pile of wet faeces below the entrance to the tunnel. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DE]

On some trees the feeding scars and burrows of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), are grown over, e.g. a healthy Carpodetus serratus (putaputaweta). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DD]

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. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DB]

Old feeding site of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), in trunk of Kunzea ericoides (Myrtaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 15I3]

Active feeding site of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), in branch of Griselinia littoralis (Cornaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 15HX]

Active feeding site of a newly established burrow of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), in branch of Pomaderris apetala (Rhamnaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 15HZ]

Pathogens and predators of puriri moths are known, but no parasitoids have been found.

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. Dr. Miller reports that Maori also used puriri moth larvae which they called ngutara, a name also used for other wood-boring larvae.

Pathogens

Dr Grehan in his extensive study of puriri moth found three fungi and bacterium, Bacillus sp., infesting caterpillars and pupae. The only definitely named fungus, Cordyceps 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.

Diagrams illustrating the position and form of diseased puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillars. Creator: JR Grehan and PJ Wrigley. © Drawings published in New Zealand Entomologist, 1984, 8: 61-63, Figs 1-4. [Image: 3DH]

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. The caterpillar is killed by gum flooding the burrow.

Newly established tree phase puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillar burrow in a cherry tree. Note the wood fragments attached to the web cover. During the following winter, tree gum oozed out of the burrow. The following summer, the tree had grown over the feeding scar and hole (right). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 3CS]

The site of a newly established puriri moth, Aenetus virescens (Lepidoptera: Hepialidae) burrow in a cherry tree. During the winter following establishment, tree gum oozed out of the burrow. The following summer, the tree had grown over the feeding scar and hole. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3D7]

Old pupal case of a puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), protruding from burrow in a puriri tree, Vitex lucens. Note how the web cover now has holes. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3D8]

On some trees the feeding scars and burrows of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), are grown over, e.g. a healthy Carpodetus serratus (putaputaweta). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DD]

On some trees the feeding scars and burrows of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae) remain exposed, e.g. Nestegis Montana). The open holes may be colonised by insects. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DG]

Some trees, such as Carpodetus serratus (putaputaweta) may suffer heavy infestations of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). An example of many burrow openings and feeding scars. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3DC]

Some trees, such as Carpodetus serratus (putaputaweta) may suffer heavy infestations of puriri moth, Aenetus virescens (Lepidoptera: Hepialidae); an example of damaged wood in a split trunk. Creator: DSIR photographers. © Landcare Research. [Image: 3D3]

Puriri moth , Aenetus virescens (Lepidoptera: Hepialidae), caterpillars feeding in thin tree trunks can almost ring bark the tree. This Carpodetus serratus (putaputaweta) sapling survived. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 3D9]

Puriri moth, Aenetus virescens (Lepidoptera: Hepialidae), caterpillars feeding under webbing on trunk of Cotoneaster glaucophyllus (Rosaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 28GL]

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/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Pests/Puriri-moth/Puriri-mothEnt16

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?

Metal outdoor signs are available for placement in reserves, Regional and National parks, urban parks and school grounds. They can be bought from Metal Images Ltd, www.metalimage.co.nz/products/botanic-labels. The Bug Signs are listed near the bottom of the ‘Fauna Species list’. The signs come in two sizes, 100 x 200 mm, 194 x 294 mm. The signs can be bought ready mounted on a stand that needs to be ‘planted’ in the ground, or they can be bought unmounted with holes for fixing into your own mounts.

The signs for Puriri moth are best placed near trees with the distinctive damage to trunks and/or branches. Trees commonly, exhibiting damage include, puriri, lacebark (Hoheria species) and Carpodetus serratus (Marble leaf, Putaputawētā). Trees with puriri moth damage usually live for many years.

Large Bug Sign (5003) for Aenetus virescens, Puriri moth, 194 x 294 mm. Creator: Metal Images Ltd. © Metal Images Ltd & Entomological Society of New Zealand. [Image: 1L15]

Small Bug Sign (5003) for Aenetus virescens, Puriri moth, 100 x 200 mm. Creator: Metal Images Ltd. © Metal Images Ltd & Entomological Society of New Zealand. [Image: 1L16]

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 2009. Ghost moth (Lepidoptera: Hepialidae) research and discovery in the Southwest Pacific. Bulletin of the Buffalo Society of Natural Sciences 38: 17-29.

Grehan JR, Care C. 2017. Colour pattern variation in puriri moth, Aenetus virescens (Lepidoptera: Hepialidae). The Weta 51: 51-57.

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/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Pests/Puriri-moth/Puriri-mothEnt16 (describes impact on wood quality).

www.nzffa.org.nz/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Pests/Puriri-moth/Puriri-MothFHnews162 (early reports of puriri moth damage to trees).

Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/.

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.

1 April 2018. NA Martin. Bug signs updated

16 October 2017. NA Martin. Life Stages and Annual Cycle and Information sources: a new sources of photographs of moths added.

6 June 2016. NA Martin. Recognition: added photos of moth and external tree damage. Other Images: images added. Host plants: names of host fungi added. Natural enemies: list of pathogens and predators added. Details of Bug Signs added.

26 July 2010. NA Martin. Caption for Image\3CL: female to male. Annual cycle: added pre-pupation web removal by caterpillar.