The larval stages have been reared in the laboratory from eggs to adults. U. assignata has 13 larval instars and larval development averaged 124.4 days. Each instar has been studied and described, with emphasis on the principal characters of the external morphology which distinguish the various instars (antennary segments, size of the compound eyes, setal arrangement on the prementum and palpus, wing sheath, tarsal segments etc.). The phenology of the species is also described.