HortFACT
Identification
Adults of the currant clearwing, known in Australia as the currant borer moth, are very distinctive. The male and female are similar in colouring and general appearance. The body is blue-black, with a purplish metallic sheen in fresh specimens. The abdomen has four narrow segmental bonds of gold-coloured scales in the male and three in the female. In both sexes there is a prominent, shield-like tuft of long scales, the anal fan at the posterior end of the abdomen. It is larger and more flattened in the male.
The transparent wings which are normally spread out while the moth is at rest, are mostly devoid of scales except on the veins, which are generally black with golden-purplish markings. A fringe of long, pale purplish scales borders the exposed posterior margin of the wings, and each forewing has an area of black scales at about two-thirds from the body.
Body length ranges from 10 to 14mm, width 2 to 3mm, and wingspan 16 to 20mm.
The olive-brown eggs are normally laid singly near the nodes or axillary buds, pruning scars, exit wounds, or under loose bark, but may be aggregated when populations are large. They are rounded-oblong in shape, measuring about 0.6mm in length by 0.4mm by 0.3mm.
The larva or caterpillar, after hatching, is creamish-brown with a brown head capsule, and around 2mm long. It tunnels through the harder conducting layers of the cane via buds, scars, wounds, and old exit holes to enter the pith, where feeding commences. Larvae pass through about six instars, reaching 15-18mm in length at maturity. The head capsule is then reddish-brown, the prothoracic shield, pale brown and the body uniformly cream in colour. The body shrinks considerably just before pupation.
The pupa, which is enclosed in a thin, brownish/grey silken cocoon within the stem, is creamy-white when first formed but hardens to a medium brown colour. About 2 days before adult emergence the pupa, averaging about 10mm in length, becomes black with the golden bands of the adult clearly visible.
Pupation occurs near an emergence hole previously cut by the mature larva. By flexing its abdomen, the pupa is able to move part-way out of the pupal chamber shortly before adult emergence.
Host plants
The main hosts are members of the genus Ribes, especially black, white, red, and flowering currants and various gooseberry cultivars. Additional hosts are also known.
Damage
Damage to buds and cane pith is caused by the feeding activities of larvae. Often the axillary buds are completely eaten out before the larvae progress to the pith region of the stem. This boring activity weakens the stems, which are then easily broken by wind or by mechanical harvesters.
Distribution
The world distribution of the current clearwing now closely follows the early spread and cultivation of currants and gooseberries. This moth occurs throughout New Zealand where suitable hosts are grown.
Life cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
One generation of this insect is normally completed annually, but where old canes are re-invaded completion of the life cycle may extend over 2 years.
Adults are on the wing from the end of October through to early January. They fly only during daylight hours, and flight is correlated closely with temperature and cloud cover. Under suitable conditions the males may form 'flight swarms' above currant plants when their numbers are large.
The eggs take about 3 weeks to hatch. Larvae feed actively in the stem during late summer and autumn, but cease feeding in winter, they then resume feeding in spring. As it approaches maturity, each larva cuts a small emergence hole through the woody tissues of the stem; this is blocked normally by construction of the silken pupal cell. After about f-6 weeks the pupa forces its way partially through the exit. The adult emerges from this pupal position, leaving the cast exuviae (pupal skeleton) behind, projecting from the exit hole.
W.P. THOMAS