HortFACT
Identification
The adult is a black and crimson moth about 20 mm long. The hind wings are entirely crimson, and each forewing has a crimson stripe and two marginal spots. Moths usually rest with the wings folded as in the above drawing. They are not very active fliers, and females in particular usually travel only a metre or so at a time.
Eggs are spherical, yellow when fresh but darkening as they develop. They are laid in clusters of 30-60, usually on the underside of leaves.
Larvae are pale yellow when they first emerge from the egg, with black heads. Later instars (larval stages) develop the characteristic black and yellow banding around the body. Early instars feed on the underside of lower leaves of ragwort plants, but later stages migrate to the upper parts of the plants where they feed preferentially on flowers. Fully fed larvae often migrate some distance before pupation . They select a dry, sheltered place usually close to the ground, such as in or under a dead log.
Pupae are sometimes parasitised by the ichneumonid wasp Echthromorpha intricatoria.
Host plants
Ragwort (Senecio jacobaea) is the natural food plant of cinnabar moth, and although the caterpillar can feed on the closely related groundsel, it is rarely found on this plant. The cinnabar moth was introduced into New Zealand in 1929 for biological control of ragwort, after extensive host specificity testing to show that it did not pose a threat to any desirable plants.
Damage
Caterpillars reduce seed production by consuming flowers, and when they occur in sufficient numbers can totally defoliate ragwort plants. However, by the end of March they have all pupated, allowing some damaged plants time to regenerate before the end of the growing season. Extensive defoliation and defloration by cinnabar moth caterpillars may induce plants that would have died at the end of their second year to become perennial, as can happen with plants that have been mown. When plants are under stress from other causes such as drought, feeding by cinnabar moth caterpillars may kill them, however.
Distribution
Cinnabar moth was first released between 1929 and 1932 on ragwort at many sites in Auckland, Taranaki, Nelson, and Southland. It subsequently disappeared from most areas, but has established in the Wairarapa, where large populations were apparent between 1969 and 1974. It has now spread through an area of the southern North Island from Wellington to Pahiatua and Palmerston North. During the 1980s caterpillars were collected from this population and reared at Lincoln . Their progeny have been released in other parts of the country, but it is not yet known whether they will persist. Initial signs of establishment on the West Coast of the South Island are promising.
Life cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
Cinnabar moth has only one generation per year. Adults emerge from October onwards, but are most common in December. Eggs are laid from November to February and take about 2 weeks to hatch. Each-female can lay up to 300 eggs. Larvae are common in the field from December to March. They pass through five instars, and are most conspicuous in the latter stages when they congregate on the upper parts of the plant. When fully fed they pupate, and overwinter as pupae. Although pupae can survive considerable desiccation they are particularly vulnerable to damp conditions, and mortality can be very high in waterlogged soils.
P. SYRETT AND H. HARMAN
Revised by R. HILL