HortFACT
The larvae are limp, flabby, greyish/yellow, and up to 6 cm long when full grown (W. umbraculata is somewhat larger). They live in underground tunnels 15-50 cm deep and often surmounted, capped, and concealed by castings of soil, droppings and debris, loosely held together by silken threads.
Feeding mostly occurs at night, and unless larvae are dug up they are seldom, if ever, seen alive. When disturbed they do not curl up, but often regurgitate droplets of brown fluid.
The pupae are dark reddish brown.
The adult may be identified by the characteristic shape of the forewing and its pattern, which consists of an irregular row of light patches. (In W. umbraculata these are fused to form a pale band.) At rest, the wings are held tent-like over the body.
Adult moths, which usually live for only 3-4 days, fly at dusk and at night and are strongly attracted to lights.
The eggs are 1 mm in diameter and white when first laid, but turn black within a day.
Host plants
The main hosts are pasture grasses, Covers, and lucerne. Damage to tussock and pampas has been recorded, and also rare instances of damage to barley and potato tubers.
Damage
The adult moth has vestigial mouth parts and so does not feed. Damage is caused by the larvae feeding on the aerial parts of plants, eating off the foliage at ground level. In pasture, W. cervinata may produce open patches in the sward and permanent changes in species composition. The effect of W. signata and W. umbraculata on pasture production IS not known.
Distribution
W. cervinata is present in improved and unimproved pasture throughout most of the country but is absent north of the Waikato River mouth on the west coast and Thames on the Coromandel Peninsula. W. umbraculata is restricted to boggy pastures in all three main islands. W. signata is characteristic of light, well drained soils from Nelson northwards. All three species are natives of New Zealand and not found anywhere else.
Life cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
Porina has only one generation per year, but the timing of this generation can vary. In many regions there are different populations giving rise to emergent adults in spring, early summer, or late summer. For practical purposes, whether taxonomic or management, the name cervinata is applied to all of these. In general, one of these populations will be consistently larger and hence cause more damage than the others, but in Otago and Southland importance can fluctuate from year to year or decade to decade between the populations emerging in early and late summer. In dry eastern districts such as Canterbury, the peak flight period is October-November and the damage caused by the feeding caterpillar becomes apparent in autumn. In wetter districts the peak flight is in mid or late summer, in which case the ensuing caterpillars do most damage in late winter or early spring.
Female moths are mated soon after they emerge from the soil and immediately begin laying eggs. They do this by flying in a strange looping fashion abut half a metre above the ground, scattering the eggs over the pasture surface. Each female can lay 1000-2000 eggs. In moist conditions the caterpillars hatch from the eggs in 3-5 weeks, and for about 6 weeks they live in the surface litter. During this period they are vulnerable to dry conditions and to trampling by livestock. They then construct a vertical, silk-lined tunnel in the soil.
Pupation occurs in the tunnel and takes about a month.
D.C.F. PERROTT revision co-ordinated by L.ROBERTS