Speargrass moth

Walker described the male adult of this species as follows:

Male. Pale fawn-colour. Abdomen very pale. Antennae serrated. Fore wings without any marks, excepting an indistinct darker dot on each of the exterior veins. Hind wings very pale fawn-colour, shining. Length of the body 10 lines; of the wings 24 lines. Hudson in his 1928 book The butterflies and moths of New Zealand described the larva of this species as follows:

The larva is very stout, bright yellowish-brown, considerably paler on the undersurface; the dorsal line is faintly indicated, the subdorsal and lateral lines are dull brown, with a chain of elongate white spots beneath each; the spiracles and dorsal surface of the posterior segments are black; there are also numerous white dots all over the larva. I. nullifera is large in size with the male of the species having a wingspan of 53 to 67 mm and the female having a wingspan of between 57 and 77 mm. The forewing colouration of specimens can vary from deep fawn to a dark grey. Of this species near relatives, I. nobilia is the most similar in appearance, but can be distinguished as a result of the deep greyish-blue sheen on that species' forewings.

It is endemic to New Zealand. I. nullifera can be found in the Tongariro National Park, along the Wellington coast, and throughout the South Island.

The adults of this species is sometimes attracted to light and have been collected via a mercury vapour light trap. The adults are on the wing from November to early April.

The larvae of this species feeds on Aciphylla species including Aciphylla aurea, Aciphylla colensoi, Aciphylla glaucescens, Aciphylla squarrosa, Aciphylla subflabellata. The larvae prefers the softer centre of the plant and its presence can be detected by the frass it produces as well as the discolouration it causes by feeding near the base of the leaves. The larvae are often found in burrows in the stem of the host plant. The pupa, which is in a loose cocoon, can be found in the leaf litter near the roots of the host plant.

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