EVALUATING THE RELIABILITY OF WING MARKINGS FOR DISTINGUISHING NOCTUA
JANTHE AND NOCTUA JANTHINA IN BRITAIN (Provisional Title)
MARK S. A. CALWAY1
1 22 Repton Road, Earley, Berkshire RG6 7LJ
Abstract
Distinguishing the Lesser Broad-bordered Yellow Underwing (Noctua
janthe) from Langmaid’s Yellow Underwing (Noctua janthina) remains a
challenge for moth recorders in Britain due to the variability and subjectivity
of wing markings. This study investigates the reliability of morphological
features, particularly wing patterns, as diagnostic tools for separating these
two species. During the 2025 flight season in Earley, Berkshire, four female
moths identified as potential N. janthina were retained, allowed to lay
eggs, and their progeny reared to adulthood. The experiment aimed to compare
the wing markings of each parent with those of their offspring, assessing
consistency and potential for misidentification. Additional analyses included genitalia
determination and DNA sequencing to corroborate visual identifications. The
findings are discussed in the context of existing literature, with implications
for the reliability of wing markings as a means of species separation and
recommendations for future recording practices.
Introduction / Background
Noctua janthe (Borkhausen, 1792), is a widespread and
frequently encountered moth in Berkshire (VC22) and moth recorders in the
region have typically reported it as Lesser Broad-bordered Yellow Underwing N.
janthe.
The situation changed on 9 July 2001, when a noctuid moth
captured at Southsea, Hampshire, was identified as N. janthina [Denis
& Schiffermüller, 1775]—the first confirmed record of this species in
Britain, documented by John Langmaid. Since this discovery, Langmaid’s Yellow
Underwing (N. janthina) has been found at additional sites across the
UK, including Berkshire, where the first specimen was recorded by Finlay
Hutchinson in Reading on 30 July 2022.
Since then, the moth, if not examined closely, has variously
been recorded as:
·
Lesser Broad-bordered Yellow Underwing N.
janthe
·
Lesser Broad-bordered Yellow Underwing (agg.), N.
janthe/N. janthina
·
Lesser Broad-bordered Yellow Underwing (agg.), N.
janthe/N. janthina/N. tertia
N. janthe and N. janthina are generally
considered two members of a two- or three-species complex, the third being N.
tertia. The earliest British record of N. tertia dates to Kent in
1992, though it was not confirmed as such until 2014, and its status as a
distinct species remains under debate among some authorities.
Materials and Methods
During the 2025 flight season in Earley, Berkshire, a
selection of potential N. janthina moths, from the many N. janthe/N. janthina
aggregate moths taken at light, were retained throughout the flight season.
Specimens from the early part of the season were placed in a freezer for later
inspection. In October, when there appeared to be evidence of migration and
many N. janthe/N. janthina moths were again appearing in the trap, a small
sample was taken. Four of the moths produced eggs while still in individual
pots, providing an opportunity to rear the resulting caterpillars. The eggs
were retained with the intention of rearing any resultant caterpillars to
adulthood.
Aims and Rationale
There has been ongoing discussion and documentation
regarding the reliability of wing markings as a diagnostic means of
distinguishing between N. janthe and N. janthina. Given the variability of
these markings, identification can be subjective. This experiment aimed to
confirm the identity of female moths that laid eggs as N. janthina, rear their
offspring to adulthood, and compare the wing markings of each parent with those
of their progeny. The goal was to assess the consistency of these markings and the
potential for misidentification without recourse to genitalia determination or
DNA sequencing.
Specimen Identification and Handling
Each of the four female moths that laid eggs was inspected
visually using hindwing upper-side and forewing underside features as described
in the literature. Those that appeared to be good candidates for N. janthina
were retained until they had laid an egg batch, after which they died. Each
adult female moth and her egg batch were labelled and kept separate to prevent
confusion. Each moth was assigned an identifying letter (A–D). The table below
summarises the specimens:
|
Identifier |
Date of capture |
Location |
Sex |
Method |
Notes on the eggs |
|
A |
2/10/25 |
Earley |
F |
MV light (e.g.) |
Hatched night of 12th/morning of 13th Oct 2025 |
|
B |
2/10/25 |
Earley |
F |
Hatched night of 13th/morning of 14th Oct 2025 |
|
|
C |
2/10/25 |
Earley |
F |
Hatched night of 13th/morning of 14th Oct 2025 |
|
|
D |
3/10/25 |
Earley |
F |
125W MV |
Hatched night of 14th/morning of 15th Oct 2025 |
Appendix: Supporting Analyses
Samples for DNA sequencing:
At the end of October 2025, four clean tubes labelled A, B, C, and D were
prepared, and at least two legs from each moth were placed into their
respective tubes. These were sent to Dr Andrew Spicer for DNA sequencing.
Samples for genitalia
determination:
In December 2025 the four female N. janthina candidates were passed to Ian Sims who relaxed and set them with the forewings positioned so that the hindwing markings could more easily be viewed.
Photos were taken of the upper and undersides of the set specimens with particular attention to the relevant wing markings.
The four moths (minus the legs sent for DNA analysis) were sent to Peter Hall for identification by genitalia determination in 2026.
Diagnostic Features
Wing Markings
According to the British Lepidoptera website, there are no
reliable forewing upper side features for distinguishing these species.
The hindwing upperside 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, while in N. janthina
the black subterminal fascia is continued along the costa and the blackish
dorsobasal smudge is darker and more extensive, so the hindwing appears black
with a central yellow spot. This difference is more apparent in male than
female N. janthina, implying sexual dimorphism.
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.
The underside of the forewing costa can also be a useful guide: in both
species, there is a narrow postmedian line crossing the underside of the costa
at about two-thirds; in N. janthe, the costa has the same colour on both sides
of this line, while in N. janthina, the costa is distinctly darker on the
proximal side. This feature is most reliable in fresh male N. janthina
specimens.
Genitalia Examination
Both DSG and Moth Dissection describe and illustrate a longer and narrower corpus bursae in N. janthe. The ratio of length to breadth of the corpus bursae is 3.6–4.5 in N. janthina and 5.5–5.7 in N. janthe according to published sources, though the author’s preparations yielded slightly lower ratios. In N. janthe (and N. tertia, if valid), a pleat is present at the junction between the ductus and corpus bursae, which was not observed in N. janthina specimens. This could provide a means of distinguishing the species, though further specimens need to be examined.
Discussion
[To be completed: This section will interpret the
findings, discuss the reliability of wing markings and other features for
identification, and provide recommendations for recorders and future research.]
- How similar or variable were the wing markings of the offspring of A compared to the wing markings of A
- How similar or variable were the wing markings of the offspring of B compared to the wing markings of B
- How similar or variable were the wing markings of the offspring of C compared to the wing markings of C
- How similar or variable were the wing markings of the offspring of D compared to the wing markings of D
References
[To be completed: List of all literature, websites, and sources
cited.]
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