BIBIONIDAE

Sinclair, Bradley J., Borkent, Art & Wood, D. Monty, 2007, The male genital tract and aedeagal components of the Diptera with a discussion of their phylogenetic significance, Zoological Journal of the Linnean Society 150 (4), pp. 711-742 : 720-721

BIBIONIDAE

Description ( Figs 3B, C , 4A, B )

Testis: Each testis is an elongate, sac-like gland, sometimes encased in a dark fat body.

Epididymis: Not differentiated.

Vas deferens: The vasa deferentia are slender and delicate, extending posteriorly to near the base of the large accessory gland complex. In Bibio Geoffroy ( Fig. 3C ) and Dilophus Meigen ( Blaschke-Berthold, 1994) , the vasa deferentia arch anteriorly and become stout, greatly expanded ducts, which extend anteriorly and then posteriorly again before entering the anterior apex of the accessory gland complex. These expanded regions appear somewhat muscular and are only closely associated and not fused medially. In Plecia Wiedemann , these expanded regions are lacking and the vasa deferentia remain slender, although fused distally throughout ( Fig. 3B ). The vasa deferentia are somewhat enlarged anteriorly in Penthetria Meigen and the ducts are fused medially as they arch anteriorly and extend to the apex of the accessory gland complex without arching posteriorly, as in Bibio . The vasa deferentia of Plecia membranifera Hardy & Takahashi were observed to be completely full of spermatozoa throughout their length ( Fig. 3B ).

Accessory gland and seminal vesicle: The accessory gland complex in Bibio and Penthetria is distinctly oval-shaped, whereas the glands are very elongate and nearly parallel-sided in Plecia . At least two distinct chambers are visible in the glands of Bibio flavihalter Hardy & Takahashi ( Fig. 4A, B ) and Penthetria funebris Meigen. Three distinct chambers are visible in excellently preserved material of Plecia membranifera ( Fig. 3B ).

Ejaculatory duct: The ejaculatory ducts are stout and apparently muscular. The duct appears divided medially in Penthetria and perhaps at least anteriorly in Bibio . The ejaculatory duct in Plecia is clothed in a dark fat body and the inner duct was not visible.

Ejaculatory apodeme, sperm pump, and aedeagus: The ejaculatory apodeme is a concave plate, which cradles the endophallus and is moved by two pairs of opposing muscles in Bibio ( Blaschke-Berthold, 1994; Sinclair, 2000: fig. 12). The ejaculatory apodeme slides in and out of the base of the aedeagus and compresses the sperm pump chamber (see ‘Remarks – features of Bibionomorpha’, below). The phallotrema is broad and flexible ( Blaschke-Berthold, 1994).

Remarks: Our interpretation of the male gonads, especially of Bibio , differs from that of Blaschke-Berthold (1994). The very small delicate testes in Bibio were omitted from her illustrations (cf. Figs 3C , 4A and Blaschke-Berthold, 1994: fig. 72). In addition, we interpret the large medially fused gland as a complex fusion, identified as the accessory gland complex, whereas Blaschke-Berthold (1994) identified these glands as simply the seminal vesicle. The glands labelled ‘akzessorische Drüse’ (aD1) are possibly homologous to vesicular glands observed in Tipulidae ( Byers, 1961; Frommer, 1963). Blaschke-Berthold (1994) made no observations on the internal divisions of the accessory gland complex (seminal vesicles sensu Blaschke-Berthold).

Remarks – features of Bibionomorpha: There have been several studies made on the male genital tract of Bibionomorpha. Leppla, Carlysle & Guy (1975) presented detailed histological sections of the mechanics of spermatophore transfer in Plecia nearctica Hardy. The most comprehensive work is that of Blaschke-Berthold (1994), who detailed the internal tract and external genitalia of five families of Bibionomorpha, including the Sciaridae and Mycetophilidae s.l. In these two families, the anteriorly directed vasa deferentia are greatly enlarged, with thickened walls ( Abul-Nasr, 1950; Blaschke-Berthold, 1994).

The male genital tract of this infraorder appears distinctly modified in comparison with the Tipulomorpha and very similar in basic configuration to Chironomoidea (+ Dixidae ) and this is especially true of Plecia membranifera . However, the length or size of the various chambers distinctly differs. The accessory gland complex also differs from the accessory glands of Mecoptera in the presence of inner chambers and the absence of appendices. Undoubtedly, the configuration of the male genital tract in Bibionomorpha reflects the production of spermatophores, the existence of which is confirmed in the Bibionidae ( Leppla et al., 1975; Blaschke-Berthold, 1994) and Sciaridae ( Eberhard, 2001) .

The mechanics of spermatophore formation or transfer in Bibionomorpha would appear to differ from Culicomorpha because of the presence of the ejaculatory apodeme in the former. The ejaculatory apodeme no longer acts as a piston to compress the sperm pump, but is drawn in and out like a spatula, apparently assisting in delivering the spermatophoreforming material into the female genital chamber ( Blaschke-Berthold, 1994; Sinclair, 2000). In contrast to the Culicomorpha , the spermatophore is actually never exchanged (at least in Bibionidae ), but remains attached to the male genitalia and functions as a channel for the passage of spermatozoa ( Leppla et al., 1975; Blaschke-Berthold, 1994). The spermatophore fluids congeal within the female genital chamber, expanding to fill the chamber ( Leppla et al., 1975). In Sciaridae , the spermatophore has been observed attached to the female genitalia ( Eberhard, 2001).

Figures

Figure 3. Male internal reproductive organs (dorsal view). A, Hesperinus rohdendorfi (Hesperinidae). B, Plecia membranifera (Bibionidae). C, Bibio flavihalter (Bibionidae), left vas deferens and testis removed (based on the specimen photographed in Fig. 4A). D, Pachyneura fasciata (Pachyneuridae). acc gl cplx, accessory gland complex; ej dt, ejaculatory duct; tes, testis; vas df, vas deferens. Scale bars = 0.1 mm.

Figure 4. Male internal reproductive organs. A, Bibio flavihalter (Bibionidae) (dorsal view). B, Bibio flavihalter (Bibionidae) (dorsal view). acc gl cplx, accessory gland complex; ej dt, ejaculatory duct; tes, testis; vas df, vas deferens. Scale bars = 0.1 mm.