Helastia alba is a moth of the family Geometridae. This species is endemic to New Zealand and is found only in the South Island. This species inhabits native forest or scrubland and can be observed in montane to subalpine Nothofagus dominant forests. It has also been observed at lower altitudes in native podocarp forests. Larvae of this species have been raised on mosses. Adults are on the wing from November to January and are nocturnal. This species is very similar in appearance to other species in the genus Helastia, but specimens can be distinguished by the dissection of their genitalia.

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