FNZ 30 - Hepialidae (Lepidoptera) - Popular Summary
Dugdale, JS 1994. Hepialidae (Insecta: Lepidoptera). Fauna of New Zealand 30, 164 pages.
( ISSN 0111-5383 (print), ; no. 30. ISBN 0-478-04524-7 (print) ). Published 01 Mar 1994
The Hepialidae in New Zealand are well known by the common name porina, but strictly this refers only to the pasture pest genus Wiseana. The economic damage to pasture grasses caused by the feeding activity of porina caterpillars is second only to that of grass grubs.
Perhaps better known to many New Zealanders is the puriri moth, Aenetus virescens. The large, conspicuous, green-winged adults with glowing red eyes are attracted to street lamps and domestic lighting in the North Island.
Seven genera of Hepialidae are recognised in New Zealand, comprising 27 species, several of them newly described. Some are apparently very localised, and there is a focus of species diversity in the southern South Island, particularly in native forests and in high-country shrub/grassland and swampy habitats. All species are endemic.
Hepialidae are mostly moderate-sized moths with a wingspan in the range 45-70 mm, though smaller (35 mm) and much larger (up to 150 mm) examples are known. The often highly patterned wings are usually large and strong, and many species are known to be swift fliers, though tending not to disperse far from their place of origin. Large females of the puriri moth are the largest and heaviest Lepidoptera native to New Zealand.
From a conservation perspective it is important to realise that most New Zealand hepialid moths are not pests, but are native species occurring nowhere else. Many are localised, perhaps rare, and possibly threatened with extinction. More information is needed about their biology and status.
The biology of the puriri moth has recently been closely studied. Young larvae hatch from eggs in the forest leaf litter, where they begin their development. They then moult into a conspicuous 'transfer phase' form which moves out of the litter and climbs the trunk of a suitable host tree. Many tree species, both native and introduced, are used as hosts, of which the puriri is but one.
The larva forms a typical '7'-shaped tunnel and a silk-covered external feeding scar over the entrance. Once established the larvae moult into the 'tree phase', in which they complete their growth. The entire larval period may take as much as 4 years, and mature larvae may exceed 100 mm in length. Pupation occurs inside the shaft, and most adults emerge in spring or early summer.
Porina moths too have an early litter-phase larva, which subsequently digs a burrow more or less vertically into the soil. The shaft-phase larva lines the burrow with silk, and constructs a silken 'runway' from the entrance out to its feeding area. Emerging at night, the caterpillar cuts grass shoots at the base and drags them back into the burrow, to be consumed later. Cut plant material and frass (faecal pellets) may be stored in side chambers excavated from within the main burrow. The life cycle is completed in 1 year, and adults may be on the wing between September and April, depending on species and locality.
Adult hepialids have no functional mouthparts, and their lifespan is consequently brief. Allowing for predation by morepork owls, cats, and possums the average is probably less than a week. They emerge and fly in the late afternoon or around dusk, and may be on the wing for only an hour or so, especially the males. For most species emergence is greatest in warm, misty weather, giving rise (in crepuscular species) to 'flight nights'. Females ready for mating attract males to them by releasing a 'sexual scent' called a pheromone. Handling a recently emerged female makes one's fingers attractive to any males circling nearby!