Separation of these two species is covered by the Difficult Species Guide and at Moth DIssection.
There are no reliable forewing upperside features.
There are no reliable forewing upperside features.
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Noctua janthina
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Noctua janthe
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Hindwing upperside
This provides the best identification feature: In N.janthe it appears bright yellow with a broad subterminal fascia, and a dorsal blackish smudge continuing to the wing base, the costa being largely yellow. In N.janthina the black subterminal fascia is continued along the costa and the blackish dorsobasal smudge is darker and more extensive so that the hindwing appears black with a central yellow spot, rather than yellow with a black border. This hindwing difference is more apparent in male than female N.janthina (implying sexual dimorphism in N.janthina).
This provides the best identification feature: In N.janthe it appears bright yellow with a broad subterminal fascia, and a dorsal blackish smudge continuing to the wing base, the costa being largely yellow. In N.janthina the black subterminal fascia is continued along the costa and the blackish dorsobasal smudge is darker and more extensive so that the hindwing appears black with a central yellow spot, rather than yellow with a black border. This hindwing difference is more apparent in male than female N.janthina (implying sexual dimorphism in N.janthina).
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Forewing underside
Both species show an extensive blackish basal area and a brownish terminal band. In N.janthe the distal margin of the black basal patch extends between veins as teeth and the terminal colour is yellow-brown; in N.janthina the distal margin is smooth and the terminal colour dull brown. DSG suggests that these forewing underside features do not provide absolute separation of the species. Not mentioned in the references, but when selecting specimens for confirmation of identity as N.janthina we used the underside of the forewing costa as what proved to be a reliable guide. In both species there is a narrow (postmedian) line crossing the underside of the costa at ~2/3; in N.janthe the costa has the same colour on both proximal and distal sides of this line; in N.janthina the costa is distinctly darker on the proximal side of the line. This feature is quite easy to see with the moth in a specimen pot (see image right). |
N.janthina
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N.janthe
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Male genitalia
Both DSG and Moth Dissection describe and illustrate the only genital difference as affecting the basal diverticulum of the everted aedeagus, the diverticulum being narrow in N.janthina and broad in N.janthe. However, this feature is variable within each species and intermediates are found. I have so far been unable to demonstrate this feature in any convincing way.
Both DSG and Moth Dissection describe and illustrate the only genital difference as affecting the basal diverticulum of the everted aedeagus, the diverticulum being narrow in N.janthina and broad in N.janthe. However, this feature is variable within each species and intermediates are found. I have so far been unable to demonstrate this feature in any convincing way.
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Female genitalia:
Both DSG and Moth Dissection describe and illustrate a longer and narrower corpus bursae in N.janthe. In the specimens shown in DSG and at Moth Dissection the ratio of the length:breadth of the corpus bursae (length measured from the anterior sclerotised margin of the ductus bursae to the apex of the corpus bursae; breadth at widest point) gives 3.6-4.5 in N.janthina and 5.5-5.7 in N.janthe.
In the natural position there is a pleat (directed ventrally then anteriorly) at the junction between the ductus and corpus bursae. The length of ductus between the anterior end of its sclerotisation and the posterior edge of the appendix bursae varies with the degree to which this pleat has been unfolded in a set specimen.
Both DSG and Moth Dissection describe and illustrate a longer and narrower corpus bursae in N.janthe. In the specimens shown in DSG and at Moth Dissection the ratio of the length:breadth of the corpus bursae (length measured from the anterior sclerotised margin of the ductus bursae to the apex of the corpus bursae; breadth at widest point) gives 3.6-4.5 in N.janthina and 5.5-5.7 in N.janthe.
In the natural position there is a pleat (directed ventrally then anteriorly) at the junction between the ductus and corpus bursae. The length of ductus between the anterior end of its sclerotisation and the posterior edge of the appendix bursae varies with the degree to which this pleat has been unfolded in a set specimen.
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All images © Chris Lewis
Page published 31/07/2017
