This species was described by Edward Meyrick in 1929 using a male specimen collected by George Hudson at Point Howard in Lower Hutt in March.

Forewings elongate, slightly dilated, costa gently arched, apex obtuse, termen obliquely rounded; grey-whitish irrorated grey; an irregular grey streak mixed blackish from base of costa above fold to elongate black plical stigma; light grey suffusion with irregularly scattered black scales extends also to dorsum at base, over posterior part of cell, above fold to extremity, and forms an irregular excurved fascia at 2⁄3, a terminal fascia confluent with this beneath, and spots on costa at 1⁄3 and 4⁄5; an elongate blackish mark representing second discal stigma beneath this a spot of ochreous-whitish suffusion: cilia whitish mixed grey and blackish-grey except towards base.

[5] However I. rigescens lacks the tufted second segment of the labial palp of T. sublitella so the two should be easy to distinguish on close examination.

[6][7] This species has only been found at its type locality of Point Howard, Lower Hutt in Wellington.

[5] This species has been classified as having the "Data Deficient" conservation status under the New Zealand Threat Classification System.