Colobaea pectoralis (Zetterstedt, 1847)

Bratt, Albertus D., Knutson, Lloyd V., Murphy, William L. & Daniels, Anthony A., 2020, Biology, immature stages, and systematics of snail-killing flies of the genus Colobaea (Diptera: Sciomyzidae), with overviews of aspects of the tribe Sciomyzini, Zootaxa 4840 (1), pp. 1-64 : 42-43

Colobaea pectoralis

Egg ( Fig. 5 ) (based on three specimens from Hillerød, Denmark). Length 0.60–0.80 mm; greatest width 0.20–0.30 mm. Robust, anterior end smoothly rounded, ventral surface slightly more convex than dorsal surface in lateral aspect. Chorion very finely granulose and punctate; longitudinal ridges strongest, producing noticeable striated appearance.

First-instar larva (based on five specimens from Hillerød, Denmark). Length 1.00– 1.20 mm; greatest width 0.10–0.20 mm. Basal rings of sensory papillae dark, large; post-oral spinules long, slender, lightly pigmented. Cephalopharyngeal skeleton ( Fig. 9 ) brown, 0.10–0.11 mm long. Indentation index 80; mouthhooks short, broad.

Posterior end with three pairs of marginal lobes and lateral protuberances; spinules sparse, lightly pigmented. Spiracular tubes long, cylindrical, 0.14 mm long. Float hairs long, slender.

Second-instar larva (based on three specimens from Hillerød, Denmark). Length 1.5–2.5 mm; greatest width 0.3–0.5 mm. Anterior spiracles small, stalk narrow, 16–18 marginal papillae tightly enclosed by integument. Cephalopharyngeal skeleton ( Fig. 10 ) 0.14 mm long. Indentation index 87. Ventral arch with 18–20 teeth. Spinules present on lateral pads. Segment III without ventral patch.

Posterior end with four pairs of lobes; dorsal pair very small; lateral protuberances large, blunt, anterior to disc; ventral and ventrolateral pairs about half the size of lateral pair, rounded at apices. Mammillae present at bases of ventral lobes. No float hairs.

Third-instar larva (based on 10 specimens from Hillerød , Denmark). Length 4.2–5.5 mm; greatest width 0.8–1.2 mm. Body form slender, spindle shaped, circular in cross section, not flattened and expanded posteriorly. Anterior spiracles with 14–16 marginal papillae, without prismatic spots, papillae not tightly covered by integument ( Fig. 32 ) .

Cephalopharyngeal skeleton 0.35 mm long ( Figs 36–37 , 41 ). Dorsal cornu large, with small, incomplete window; ventral cornu slender, elongate, with small, incomplete window; dorsal bridge prominent. Indentation index 75. Mouthhooks long, anteroventrally directed; ventral arch large, with 20–22 teeth.

Spinules sparse, lightly pigmented. Segment III with no spinule patch, segment IV with single ventral patch, segment V with two-part patch, segments VI–XII with three-part patches. Lateral pads with spinules. No dorsal spinules.

Posterior end with four pairs of lobes ( Fig. 17 ). Ventral and ventrolateral pairs large, subequal; lateral protuberances at anterior margin of disc large, dorsal pair very small. Mammillae at bases of ventral lobes. Ventral and ventro-lateral lobes and lateral protuberances with 3–4 rows of encircling spinules. Peritremes, slit margins, and stigmatic scars darkly pigmented.

Puparium ( Figs 23, 26 ) (based on 10 specimens from Hillerød , Denmark). Length 4.9–6.2 mm; greatest width 1.4–1.6 mm. Shaped to fit inside snail shell. Crescent shaped in lateral aspect. In dorsal aspect, first three segments widen from apex of cephalic caps, next six segments parallel sided, last segments narrowed abruptly to small posterior spiracular disc. Dorsal cephalic cap concave, next two segments convex, next four segments dorsally depressed by shell, last segments convex. First four segments dark reddish brown, last two segments lighter, middle segments lightly pigmented; dorsal surface lighter than ventral. Integument thick, finely wrinkled, with light punctations. Segmentation conspicuous, lateral intersegmental pads apparent, secondary integumentary folds not apparent. Anterior spiracles strongly protrudent anterodorsally from angles of cephalic cap. Posterior spiracular tubes protrudent. Posterior spiracular disc distorted, reduced; ventral and ventrolateral lobes visible as small welts, other lobes not apparent. Lundbeck (1923) illustrated and provided a brief description of the puparium .

For comparison with our descriptions, we cite here an English translation (from the original German) of Rozkošný’s (1967) description of the puparium and third-instar cephalopharyngeal skeleton of C. pectoralis , based on three puparia found in shells of A. vortex collected 25 March 1965, from which 2♂ and 1♀ emerged on 13 April:

“Puparium (Dimensions: 2.8–3.3 x 0.7–1.0 mm) red brown-brown. Anterior end of puparium is wide and expanded, differing from Colobaea distincta . The anterior spiracles lie at the sides of the anterior end, shaped longitudinally oval with tiny spiracular slits (about 15). Under the posterior spiracles, the remains of 2 pairs of marginal lobes are easily visible. Shape of the puparium longitudinal cylindrical adapted to the shell shape of Anisus vortex . CP skeleton (length 0.35 mm) very similar to the one of Colobaea distincta . Mouthhooks not so large. Both cornua of the pharyngeal sclerites a little less divergent, anterior bridge well developed.”

Rozkošný’s (1967) descriptions and figures were reproduced in Rozkošný (2002) and the figures in Vala (1989).

Figures

FIGURES 5–7. Eggs, lateral outline: 5, Colobaea pectoralis (Zetterstedt); 6, C. americana Steyskal; 7, C. bifasciella (Fallén). Measurement in mm.

FIGURES 9–12. Cephalopharyngeal skeletons: 9, Colobaea pectoralis (Zetterstedt), first-instar larva; 10, C. pectoralis, second-instar larva; 11, C. punctata (Lundbeck), second-instar larva; 12, C. deemingi Knutson & Bratt, second-instar larva.Abbreviations: DB, dorsal bridge; DC, dorsal cornu; HS, hypostomal sclerite; MH, mouthhook; PS, pharyngeal sclerite; VA, ventral arch; VC, ventral cornu. Measurement in mm.

FIGURES 32–35. Anterior spiracles, third-instar larvae: 32, Colobaea pectoralis (Zetterstedt); 33, C. deemingi Knutson & Bratt; 34, C. punctata (Lundbeck); 35, C. bifasciella (Fallén). Abbreviations: PrS, prismatic spot; StS, stigmatic scar. Measurement in mm.

FIGURES 36–37. Cephalopharyngeal skeletons of third-instar larvae: 36, Colobaea pectoralis (Zetterstedt), dorsal view of anterior portion; 37. C. pectoralis, ventral view of ventral arch.Abbreviations:AvP, anteroventral process of pharyngeal sclerite, DB, dorsal bridge, DC, dorsal cornu, DW, dorsal window, ES, epistomal sclerite, HS, hypostomal sclerite, LS, ligulate sclerite, MH, mouthhook, PB, parastomal bars, PS, pharyngeal sclerite, VA, ventral arch, VC, ventral cornu, VW, ventral window. Measurement in mm.

FIGURES 40–43. Cephalopharyngeal skeletons of third-instar larvae: 40, C. punctata, lateral view; 41, C. pectoralis, lateral view; 42, C. bifasciella (Fallén), lateral view; 43. C. deemingi Knutson & Bratt, lateral view. Abbreviations: AvP, anteroventral process of pharyngeal sclerite, DB, dorsal bridge, DC, dorsal cornu, DW, dorsal window, ES, epistomal sclerite, HS, hypostomal sclerite, LS, ligulate sclerite, MH, mouthhook, PB, parastomal bars, PS, pharyngeal sclerite, VA, ventral arch, VC, ventral cornu, VW, ventral window. Measurement in mm.

FIGURES 15–20. Posterior ends of third-instar larvae: 15, Colobaea americana Steyskal, caudal view; 16, C. bifasciella (Fallén), caudal view; 17, C. pectoralis (Zetterstedt), caudal view; 18, C. punctata (Lundbeck), caudal view; 19, C. deemingi Knutson & Bratt, caudal view; 20, C. punctata, lateral view.Abbreviations: DL, dorsal lobe, LP, lateral pad, M, mammillae, PaP, peri-anal pad, SpP, spiracular plate, SpT, spiracular tube, VL, ventral lobe, VlL, ventrolateral lobe. Measurement in mm.

FIGURES 23–27. Puparia: 23, Colobaea pectoralis (Zetterstedt), lateral view; 24, C. bifasciella (Fallén), lateral view; 25, C. americana Steyskal, dorsal view; 26, C. pectoralis, dorsal view; 27, C. bifasciella, dorsal view. Measurement in mm.