Catocala unijuga

Catocala unijuga
Walker, [1858]

Catocala unijuga, Worthington, Nobles County, Minnesota,
68-72mm, September 16-19, 2011, Tom Middaugh.

Tom Middaugh sent me the "plate" above, tentatively identified by himself as Catocala unijuga, but with a question of possibility of them being Catocala semirelicta.

I replied:

"Hi Tom,

"I would go with unijuga even though they are on small side of wingspan range.
1) black median band on hindwing almost reaches the inner margin; I expect it to be more distant in semirelicta;
2) there are some dark hairs in basal median area of hindwings on all three specimens, typical of unijuga; I expect a “clearer complexion” in semirelicta (no blackish grey hairs in hindwing basal median areas) This is my primary reason;
3) semirelicta usually have a lighter overall appearance to forewing ground colour, less contracting than in unijuga;
4) absence of diffuse dark bar on forewing, paralleling the inner margin, usually present in semirelicta, reduced to thick outline along inside of last inward projection on unijuga.

"I have also been told by Harry Dale King, who is quite knowledgable, that wingspan of semirelicta is usually more in 55mm range in Michigan. I wish permission to post them, credited to you, from a link on unijuga page?"

After posting this reply to Tom, I also posted the "plate" to both the semirelicta page and to the unijuga page, and I noticed an additional character which seems fairly consistent:
In semirelicta, there seems to be, in the marginal area of the forewing outer margin, moving from body to outer wing edge, 1) thick black arcs, not extending to wing veins between each pair of veins, 2) atop small whitish circles outlined in black except for outer edge of circles, 3) atop thin black arcs that run from wing vein to wing vein.

In unijuga, in the same respective areas, the 1) internal cap is thinner and almost reaches wing veins, 2) the outer circles are less distinct and greyish, 3) the outer, thinner arcs are common to both species. I do not know if this feature is consistent, but if present with other characters mentioned above, it will add additional confidence in determining the two species.

Catocala semirelicta, Wagner Bog, edmonton, Alberta, August 2, 1998, SEM.

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Superfamily: Noctuoidea
Family: Noctuidae
Group: Noctuinina
Subfamily: Catocalinae
Genus: Catocala, Schrank, 1802


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