Microdon myrmicae, Schonrogge

Scarparo, Giulia, Wolton, Robert, Molfini, Marco, Pinna, Luigi Cao & Ulio, Andrea Di Gi-, 2020, Comparative morphology of myrmecophilous immature stages of European Microdon species (Diptera: Syrphidae): updated identification key and new diagnostic characters, Zootaxa 4789 (2), pp. 348-370 : 354-357

Immature stages of Microdon myrmicae

Egg

Figs 1 , 11

Width = 587.4 ± 36.61 µm; length = 1.08 ± 0.03 mm (n = 10).

First instar larva

Figs 2−6 , 11 , Supplementary Material 1

Body width = 679.5 ± 55.42 µm; body length = 0.996 ± 0.08 mm (n = 10). Body features. Body with regularly rounded sides. Four longitudinal grooves present dorsally ( Fig. 2A ) dividing dorsal body surface into five main longitudinal fields: one medial, two lateral and two external fields. Medial field partially divided into two halves by a longitudinal, medial line. Dorsal surface with regularly spaced “flower-like” sensilla ( Figs 3A, E ): medial field with two longitudinal rows of nine sensilla; each lateral field with 13 sensilla arranged in two rows (seven along lateral groove and six along medial groove); each external field with one row of 10 sensilla. Each sensillum ( Fig. 3E ) composed of a cylindrical base, with many imbricate, thick sculpticels, apically with a medial flower-like structure with a variable number (5–10) of long lobes, pointed at tip, encircling a medial dome. Ventral surface covered medially by pointed microsculpture, finely pilose on sides. Ventral flower-like sensilla ( Figs 3C, G ) similar to dorsal ones except for flat, soft, unsculptured base and flat, thin, distinctly pointed lobes. Pseudocephalon. Two pairs of sensorial organs on dorsal surface of pseudocephalon ( Figs 4E, G ), one anterior ( Fig. 4E ) and one posterior ( Fig. 4G ), each composed of clusters of four short and one long trichoid sensilla emerging from bulbous, hollow base. Posterior spiracular tubercle. Impair respiratory structure, elongated in shape; surface of spiracular tubercle with peculiar microsculpture, completely covered by imbricate, sclerotised scales with an irregularly indented apex ( Fig. 5A ). Apex of tubercle with two circular smooth plates, slightly convex ( Fig. 5C ). Marginal band. Distinctly long fringe, length of processes regularly varying, showing eight waves on each side ( Figs 2A, E , 6A, C, E ). Each individual process composed of an elongate stem and an apical fringed brush ( Figs 6A, C, E ); the stem showing two very different surfaces: dorsal surface apparently articulated with 4–5 imbricated joints, the distal one fringed apically ( Figs 6A, E ); ventral surface completely smooth ( Fig. 6C ).

Third instar larva

Figs 7−9 , 11

Body width = 4.5 ± 0.7 mm; body length = 6.1 ± 0.8 mm (n = 10). Dorsal reticulation. Dorsal reticulation reduced to a narrow, lateral belt around the perimeter of abdomen ( Figs 7A, B ). Each reticulation process showing sub circular groups of 5–9 umbrella-like structures with a flattened, circular apex ( Figs 7A, B ). Posterior spiracular tubercle. Dome shaped with two round holes spaced 1.2 times as long as their diameter; apex divided into two halves ( Figs 8A, B ) by a narrow furrow showing irregular plates. Marginal band. Processes on the marginal band short and thick, set close to one another, parallel, radially projecting, with suboval basal “joints”, not imbricated, the last one produced into a flat medial brush. Processes on the marginal band of three types ( Figs 9A, B ): type one basally 4–jointed and apically single and flat, with medial brush 2–lobed; type two basally 3–jointed and apically bifurcate, with medial brush 1–lobed; type three basally 3–jointed and apically produced into a group of three spiniform setae. Type one and type two regularly alternating in sequence, type three irregularly present between two type one processes.

Puparium

Figs 10 , 11

Body width = 6.1 ± 0.5 mm; body length = 7.9 ± 0.7 mm (n = 10). Anterior spiracular tubercles. Length of each tubercle about 1.4 times as long as wide, conical, tapering at the apex ( Fig. 10A, B ), smooth at the base, with the apex furrowed by about 150 respiratory fissures ( Figs 10A ); each fissure laying on a small papilla ( Fig. 10B ).

Figures

FIGURE 1. Egg of M. myrmicae (A, C, E) and M.analis (B, D, F): A, B—lateral view; C, D—detail of anterior pole with micropyle area. E, F—chorion microsculpture of volcano-like processes. A, B = 500 µm; C = 100 µm; D, E = 50 µm; F = 40 µm. ASl, alveolate slope; Cr, crater; MA, micropyle area; RP, radial projection; VP, volcano-like process.

FIGURE 2. First instar larvae of M. myrmicae (A, C, E) and M. analis (B, D, F): A, B—dorsal view; C, D—lateral view; E, F—ventral view.A–F = 500 µm. AO, anal opening; LLb, lateral lobe; MrB, marginal band; MG, medial groove; MrS, marginal stripe; PC, pseudocephalon; PSprTu, posterior spiracular tubercle; VLb, venteral lobe; WMrB, waves of marginal band.

FIGURE 3. Details of first instar larvae of M. myrmicae (A, C, E, G) and M. analis (B, D, F, H): A, B—dorsal microsculpture; C, D—ventral microsculpture; E, F—dorsal flower–like sensilla; G, H—ventral flower like sensilla.A, B, C, D = 100 µm; E, F, G = 10 µm; H = 30 µm. FS, flower-like sensilla.

FIGURE 4. Pseudocephalon of first instar larvae of M. myrmicae (A, C, E, G) and M. analis (B, D, F, H): A, B—dorsal view; C, D antennomaxillary lobes; E, F—anterior sensorial organs; G, H—posterior sensorial organs. A = 100 µm; B = 200 µm; C = 40 µm; D = 50 µm; E, F = 30 µm; G, H = 10 µm. Ant, antenna; Asn, anterior sensillum; MxPlp, maxillary palp; Psn, posterior sensillum.

FIGURE 5. Posterior spiracular tubercle of first instar larvae of M. myrmicae (A, C, E) and M. analis (B, D, F): A, B—anterior view; C, D—apical view; E, F—lateral view. A, C = 100 µm; B–, D= 50 µm E = 200 µm. ReFis, respiratory fissures; SprPlt, spiracular plate.

FIGURE 6. Marginal band of first instar larvae of M. myrmicae (A, C, E) and M. analis (B, D, F): A, B—dorsal view; C, D—ventral view; E, F—detail of processes, dorsal view.A = 100 µm; B, C, D = 50 µm; E = 40 µm; F = 20 µm. FS, flower–like sensilla; IJ, imbricate joint; SpS, spiniform setae; WMrB, waves of marginal band.

FIGURE 7. Dorsal reticulation of third instar larvae of M. myrmicae (A, B), M. analis (C, D) and M. devius (E, F); left, general view; right, detail of single reticulation processes. A = 400 µm; B = 50 µm; C, E = 500 µm; D = 100 µm; F = 200 µm.

FIGURE 8. Posterior spiracular tubercle of third instar larvae of M. myrmicae (A, B), M. analis(C, D), M. devius (E, F) and M. mutabilis (G, H); left, anterior view; right, apical view. A–H = 500 µm. ReFis, respiratory fissures; RH, respiratory hole; SC, smooth crown.

FIGURE 9. Marginal band of third instar larvae of M. myrmicae (A, B), M. analis (C, D) and M. devius (E, F); left, dorsal view; right, detail of marginal band. A = 500 µm; B, E = 300 µm; C = 100 µm; D = 50 µm; F = 200 µm.

FIGURE 10. Anterior spiracular tubercles of puparia of M. myrmicae (A, B), M. analis(C, D), M. devius (E, F) and M. mutabilis (G, H); left, lateral view; right, detail of respiratory fissures. A, E, G = 500 µm; B, F, H = 100 µm; C = 400 µm; D = 50 µm. ReFis, respiratory fissures.

FIGURE 11. Eggs of M. myrmicae trapping small drops of water (pointed with red arrows) with their volcano-like processes (A); third instar M. myrmicae larvae with larvae and workers of Myrmica scabrinodis (B); third instar larva and first instar larva (red arrow) of M. myrmicae with M. scabrinodis larvae, ventral view (C); M. myrmicae adult emerging from puparium, anterior view (D); two M. analis pupae and a puparium (E); M. devius pupa (F).