The Preimaginal Stages of Cryptotylus unicolor (Wiedemann) and Tabanus nebulosus ornativentris Kroeber (Tabanidae-Diptera-Insecta)

The Preimaginal Stages of Cryptotylus unicolor (Wiedemann) and Tabanus nebulosus ornativentris Kroeber (Tabanidae-Diptera-Insecta)

Vol. 93(1): 91-97

S Coscarón/ ⁺ , OA Mancebo*, CL Coscarón-Arias**

Facultad de Ciencias Naturales y Museo, 1900, La Plata, Argentina *Centro de Diagnóstico e Investigaciones Veterinarias (CEDIVEF), 3600 Formosa, Argentina **Facultad de Ciencias Agrarias, 8324 Cinco Saltos,

Río Negro, Argentina

A larva with peculiar very long pubescence on the integument, the pupa of Cryptotylus unicolor, and the larva and pupa of Tabanus nebulosus ornativentris are described and illustrated.

Key words: description - larva and pupa - Neotropical horseflies

The female pupa was the only known preimaginal stage of Cryptotylus unicolor (Coscarón & Poi de Neiff 1996). From larvae collected on Pistia stratiotes (repollito de agua) in lagoons of Chaco geographic area, we obtained mature larvae, pupae and imagoes of both sexes of C. unicolor. From the same place we collected another larva that changed to the pupa stage in the laboratory, emerging finally as a female corresponding to Tabanus nebulosus ornativentris. This taxon was considered a subspecies due to morphological and tinctorial differences with the typical T. nebulosus DeGeer that has a northern distribution (from Belize to Surinam and Mato Grosso). The subspecies ornativentris is restricted to the Chaco area in Paraguay, Bolivia and northern Argentina. The pupa of T. nebulosus described by Goodwin and Murdoch (1974), originated from Panama in the typical area of nebulosus s. str. is found. Because the pupae collected by us showed some differences from the pupa collected in Panama we include here a description of the pupa of T. n. ornatriventris as well as the previously unknown larva.

REFERENCES

Specimens were collected in Formosa province, in ponds around CEDIVEF (Centro de Diagnóstico e Investigaciones Veterinarias, Formosa) south of Formosa City on Highway 14. Larvae were found living on water lettuce, Pistia stratiotes. Live material was maintained individually in vials, with humid cotton until pupation, and subsequent emergence of imagoes. For morphological studies, larvae were fixed in boiling water and stored in 70% ethanol. Larvae and pupae were examined with stereoscopic microscope. C. unicolor larvae were fixed in glutaraldehyde for scanning electron microscope studies. Exuviae of larvae were mounted on slides for compound microscopic studies. Specimens are in the Museo La Plata collection.

Cryptotylus unicolor

Mature larva: robust (relaxed 20 mm, fixed 30 mm long). Color in life grayish green, lighter ventrally, tegumental ornamentation with longitudinal pale striations of variable intensity on the different specimens, showing dorsally one median and 1+1 submedian, 2+2 laterally, and ventrally 1+1 submedian (Fig. 1). Integument with abundant pubescence constituted by long ciliae (0.06-0.08 mm), arranged in differing shapes from subtriangles to subquadrates 0.1-0.16 mm wide (Figs 6, ^9-14). Head capsule yellow brown, length 2.6 mm. Antennae with the third article 0.35-0.40 times longer than the second (Figs 2, 3); mandible length 1.5 mm with 21-23 ser-rulations; maxillae, clypeus, labrum and prementum as shown in Figs 2-5. Thoracic segments with 4-6+4-6 trichomes each 0.4-0.5 mm long and bearing one to three branches emerging from the base (Figs 2, ⁹). Tegumental longitudinal striations on the anterior third of the segment, separated by 0.0077-0.023 mm. Abdominal segments II-VII with three pairs of pseudopods: 2 dorsal, 1+1 lateral and 2 ventral (Fig. 1); the dorsal pseudopodia on the first abdominal segment appear fused; only the dorsal pseudopods are well developed, the ventral pseudopodia are small and the lateral pseudopodia are inconspicuous. Pseudopod trichomes are variable in size and shape, single to medio-distally and divided in to 2-6 branches (Figs 6, ¹⁰), length 0.2-0.35 mm. There are 14-16 abdominal trichomes on each segment, length 0.5 mm. Anal segment (eigth abdominal segment) 2.5-3.5 mm long; anal lobe fringed with abundant pubescence 0.06-0.08 mm long (Figs 7, ¹³). Respiratory siphon 0.9-1.1 mm long, showing longitudinal striations, and 1+1 dorsal, 1+1 ventral, 1+1 medio lateral trichomes with a group of 2-3 hairs inserted apically (Figs 8, ¹⁴); tracheae relativeliy short 0.6-0.7 mm long.

Pupa: general aspect and morphology of frontal plate, thoracic peritreme, and aster of female as in Figs 15-19, male pupa not different from female except for the anal segment; except for 11-17 dorso-lateral spines left and right respectively and 18-28 ventrolateral spines on left and right respectively (Fig. 20). Length of male aster tubercles are: dorsal 0.5-0.7 mm, lateral 0.25-0.5 mm and ventral 0.2-0.4 mm. Variation in spine number of anal segment in the female are: dorsolateral 13-19 and ventrolateral 12-18.

Material examined: six males and eleven females reared in the laboratory from larvae collected on P. stratiotes, in lagoons near Formosa city during October, November and December, col. O Mancebo.

Discussion: the abundant body pubescence, plus the greenish gray coloration with longitudinal light stripes, number and disposition of pseudopods in larvae show a strong resemblance to Chlorotabanus. This is reinforced by aspect of the adults and demostrates the close relationships of these two genera.

Tabanus nebulosus ornativentris

Mature larva: (material observed in life and described from exuvia). Large 33 mm. Uniformly whitish, without strong contrasting colors, marked with light grayish pubescent. In general aspect is like T. claripennis (Bigot) but larger than this species larvae (Coscarón & Led 1969). Third antennal article 0.44-0.57 times longer than the second. Mandible 1.1 mm long with 12-13 serrulations. Thoracic and abdominal segments with homogeneous, short pubescence constituted of microtrichiae forming a ring on the anterior border which is continued distally near the middle of the segment by thick stripes. The remainder of the integument is bare with longitudinal striations 0.007 mm wide. Abdominal segments show an anterior pubescent ring shorter than in the thorax. Just behind the pubescent area, are the pseudopods on the II-VII abdominal segments. They have robust spines 0.6-0.7 mm length (Fig. 22). The pseudopods form a near continuous wide ring on the anterior third portion of the segment. The anal lobes were fringed by pubescence formed of thin spines 0.6-0.7 mm length (Fig. 21). Traqueal ducts 1.5 mm length.

Pupa female: 29 mm length, yellowish brown. Tubercle callus sharply ridged 0.5 wide and 0.7 mm high above median cleft; frontal tubercles well evident 0.5 mm long by 0.38 mm wide at the base, pointed slightly apically, antennal ridge with two prominent elevations apically and subacute 0.52 mm high. Antennal sheaths 0.75 mm long and 0.52 mm wide at base; antero and postero-orbital setae emerging from a prominet tubercle; vertexal tubercles well evident (Figs 24, 25). Thoracic spiracle with spiracular prominences well evident showing hard curvature 1,1 mm length and 0,38 mm high over thorax surface (Fig 26). First abdominal segment distally bordered by a single fringe of short spines; II-VII combs with bi or triseriate longer spines. Tergite VII comb mostly uniseriate with 41 spines relatively short and uniformly distributed with 1+1 median spines about 4-5 times longer and posteriorly dispossed; lateral and ventral long spines are also present (Fig 23). Dorsolateral comb of preanal segment with 27-28 relatively short and robust spines on each side, ventrolateral combs with 8-9 spines (Figs 27, 28); dorsolateral and ventral tubercles of aster 0.33-0.25-0.25 mm long respectively, no additional accessory pairs of tubercles on the midline.

Material examined: one female developed from a mature larva to a pupa in the laboratory. The larva was collected from Formosa, on P. stratiotes. The same lagoons also support larvae of Myiotabanus barrettoi, Lepiselaga (L.) crassipes, T. claripennis, T. pungens and C. unicolor, collected by O Mancebo.

Discussion: the T. nebulosus ornativentris pupa examined showed some differences from the pupal description of T. nebulosus by Goodwin and Murdoch (1974). There are also differences in the imagoes (Coscarón 1979) which are listed in Table.

The differences showed in the Table helps to justify the existence of the subspecies ornativentris from the southern area in accordance to Fairchild and Burger (1994).

To Nélida R Caligaris for illustrations and CEDIVEF personnel for help in the larvae collection work.

⁺Coresponding author. Fax: [phone]

Received 14 July 1997

Accepted 1 October 1997

• Coscarón S 1979. Notas sobre Tabánidos Argentinos XV. El género Tabanus Linnaeus (Diptera-Insecta). Obra del Centenario del Museo de La Plata 6: 251-278.
• Coscarón S, Led JE 1969. Contribución al conocimiento de Tabanus claripennis (Bigot) con especial referencia a la morfologia y biologia de sus estados preimaginales. Analecta Veterinaria 1: 13-15.
• Coscarón S, Poi de Neiff A 1996. The pupa of Cryptotylus unicolor (Wiedemann) (Diptera-Tabanidae). Rev Asoc Cien Nat Litoral 27: 65-68.
• Fairchild GB, Burger JF 1994. A Catalogue of the Tabanidae (Diptera) of the Americas South of the United States. Mem Am Entomol Inst (Gainesville) 55: vii+ 249 pp.
• Goodwin JT, Murdoch WP 1974. A study on some inmature. Neotropical Tabanidae (Diptera). Ann Entomol Soc Am 67: 85-133, 42 pls.

Cryptotylus unicolor, larva (photographs). Fig. 9: trichome and groups of ciliae of tegument pubescence of thoracic segment, (tr.: trichome). Fig. 10: general view of pseudopodia. Fig. 11: tegument pubescence groups bordered by stripes of longitudinal tegument striations. Fig. 12: tegument pubescence groups with high magnification. Fig. 13: anal segment in ventral view showing the anal lobes. Fig. 14: siphon scarcely emerged in posterior view (tr.: trichome).

Publication Dates

• Publication in this collection
  08 Oct 1998
• Date of issue
  Jan 1998

History

• Accepted
  01 Oct 1997
• Received
  14 July 1997