Tirumala septentrionis (Butler, 1874)

Shilpa, M. P., Anand, P. P., Shibu Vardhanan, Y. & Manogem, E. M., 2023, High and lowland dependent wing phenotypic variation of the dark blue tiger butterfly, Tirumala septentrionis (Butler, 1874) (Lepidoptera: Nymphalidae) with FE-SEM wing scales nanomorphology, Zoologischer Anzeiger 302, pp. 131-145 : 138-140

3.8. Wing scale patterns of Tirumala septentrionis a. Forewing scale patterns

The trend of male and female forewings of T. septentrionis is a of brown area filled with patches of bluish-white spots or streaks. The electron microscopic examination revealed that the male and female wings of the dark blue tiger butterfly of brown regions were covered with two types of scales, cover scale and ground scales marked with ragged edges ( Fig. 10A–D ). Cover scales are more elongated than ground scales, with the presence of three to four rough edges ( Fig. 10E ). However, their nanomorphologies are similar in appearance, i.e., both have a typical lamellar structure. Cover scales partly overlap ground scales and are densely packed in appearance. The upper lamina of the scales features horizontal struts known as ridges, and each scale consists of about 25–30 ridges ( Fig. 10E ). The ridges are connected vertically with cross ribs ( Fig. 10F ).

The scales present in the bluish-white region of male and female forewings of T. septentrionis shares a different arrangement pattern. Each scale lies separately, and they are not densely packed ( Fig. 10G and H ). Overlapping of two adjacent scales are absent. Each scales contain 15-20 ridges which are interconnected with cross ribs ( Fig. 10I ). Approximately 30–40 cross ribs are present in between the two ridges ( Fig. 10I ). Further, it is noted that the ridges displayed a serrated appearance ( Fig. 10J ).

The male and female forewing scales present in both regions of brown and bluish whit areas exhibits different arrangements. The present investigation shows that the brown and bluish-white regions of forewings in male and female T. septentrionis from Mlp and Wyn populations shares a similar pattern.

b. Hindwing scale patterns

Male and female hindwings of T. septentrionis exhibits brown and bluish-white regions encases with scales. Scales present in the brown region are densely packed with cover and ground scales ( Fig. 10 K-N). However, slight difference is observed in the structure of the scales present in the brown region of the hindwing. The most noticeable feature observed is that cover scales have smooth edges instead of ragged edges ( Fig. 10O ). Moreover, the structure of ground scales is similar to the scales present in the forewing, with rough edges. Cover scales partly overlap ground scale and consists of about 25–30 ridges ( Fig. 10P ) and, in turn, are connected by cross ribs ( Fig. 10P ).

The scanning electron micrographs show that the scales present in the bluish-white region of the hind wing remain separately and are not densely packed ( Fig. 10Q ). The scales are alternately arranged and are fixed in the socket with pedicel ( Fig. 10R ). It is also noticed that no overlapping occurs between two adjacent scales. The presence of 15–50 ridges in scales and they are interconnected with about 30–40 cross ribs ( Fig. 10S ). In the hindwing of male and female of T. septentrionis of Mlp and Wyn population displayed the same scale pattern in brown and bluish-white areas.

c. Morphology of male pouch scales

The striking feature of male T. septentrionis is noted for a pouch or a sac located in the hindwings, filled with androconia scales. Generally, the structure of the pouch is pendulous and flat, situated near the cell of the hindwing, containing numerous scent scales or androconia. The pattern of scales organization is just like overlapping tiles on a roof ( Fig. 10T and U ) and they are densely packed. Each scale consists of about 25–30 longitudinal ridges and are in turn connected by cross ribs. Also, it is seen that each scale possesses ragged edges ( Fig. 10 V-X). Further, the in our study showed that the pouch scales of T. septentrionis of the two areas analyzed exhibited similar scale pattern, and no variations were evidenced.

Figures

Fig. 10. FE-SEM image analysis of T. septentrionis. Forewing brown regions (A–F), and bluish-white regions (G–J) of T. septentrionis. Hindwing brown regions (K–Q), and bluish-white regions (R–T). FE-SEM image of the male pouch scale of T. septentrionis (U–X). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)