|scientific name Digrammia setonana |
Montane coniferous woods.
No Alberta data; elsewhere adults fly in June (McGuffin 1972).
A mid-sized, grey geometrid with black antemedian (AM) and post-median (PM) lines across the forewing. The dark wedges along the forewing costa typical of the genus are poorly defined in setonana. Similar to D. decorata, D. curvata and D. rippertaria, which also have the black, even forewing transverse lines. Habitat and distribution will narrow down species identity, but genitalic dissection is necessary to confirm identification; see McGuffin (1972) for genitalic keys and illustrations.
McGuffin (1972) gives a detailed description of the immature stages. The larvae are remarkable mimics of juniper twigs, complete with intricate green and white markings resembling leaf scales. In BC, this species is able to overwinter in either the egg or pupal stage, flying in June or September (Duncan 2003).
Very localized distribution in Alberta, found only in association with the host.
Larvae feed on Rocky Mountain Juniper (Juniperus scopulorum), occasionally also on Western Red Cedar (Thuja plicata); the paucity of records on cedar and the absence of setonata records over most of the range of Western Red Cedar suggests that cedar is not a regular host.
Southern BC south to UT and CA. In Alberta, known only from the Crowsnest Pass (Prentice 1963).
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