Gasterophilidae (Girschner, 1896)

Pollock, J. N., 2010, Bot flies (Insecta: Oestridae, part) and Glossinidae-Hippoboscidae derive from basal Ephydroidea, not Calyptratae, Journal of Natural History 44 (31 - 32), pp. 1929-1952 : 1947-1949

Gasterophilidae Glossinidae Hippoboscidae Oestridae s.s.

5 6

3 4 7

2

1

Ground plan of the basal ephydroid form

* Males dichoptic; antenna with dorsally cleft pedicel and an arista arising basally from the dorsal face of a decumbent first flagellomere; mouthparts of the adult of the sponging type; *thoracic suture incomplete; *greater ampulla poorly developed; *calypteres small, not covering the halteres; *subcostal vein complete; *subcostal vein straight at level of humeral break; *vein R 1 without a knob at level where subcosta joins with costa; *vein M 1 proceeding straight to trailing margin of wing; TTM fully developed; tarsi with rows of squat, close-set, dual setulae; in the male abdomen tergites six and seven free and symmetrical, *sternite six symmetrical, *all seven pairs of spiracles set in membrane not in tergites, *surstylus represented by postsurstylus and presurstylus; ejaculatory sclerite attached to aedeagal apodeme; aedeagus hook-like or bird’s head-shaped and raised on a prominence formed from the end of the aedeagal apodeme and the ensheathing cuticle; testis long and convoluted; female abdomen with an anteroventral pouch; oviparous and with three spermathecae; *eggs hatching by means of a terminal operculum; larva free-living. [*indicates the feature is carried forward to Gasterophilus pecorum unchanged.]

• Internode 2. Loss of TTM; veins R 2+3 and R 4+5 exceptionally close and parallel; cross-vein dm-cu with migratory tendencies; tergites 6 and 7 fused along a symmetrical suture.

• Internode 3. Larvae parasitic on perissodactyls (this feature might possibly belong to Internode 2); adult mouthparts not used for feeding; loss of rows of close-set setulae from the tarsi; adult with reduced chaetotaxy and clothed with longer hairs; sperm pump detached from the aedeagal apodeme and with the ejaculatory sclerite much reduced or deleted.

• Internode 4. Adult mouthparts of the blood feeding type and having a long narrow labrum; dm-cu basal of the level of the cross vein r-m; female strongly modified for adenotrophic viviparity (releasing the larvae from direct host dependency).

• Internode 5. Thoracic suture complete; greater ampulla developed; vein M 1 with a strong basal curvature, created when the cross-vein dm-cu reverted to a central position in the wing; distal part of vein M 1 beyond the level of dm-cu swinging forward; in the male a secondary transverse break in the 6-7 syntergite; the anal cerci fused below the anus; concealment at rest of the anal cerci and postsurstyli beneath the elongated epandrium.

• Internode 6. Many adaptations for the ectoparasitic life (making the tracing of homologies of many organs hazardous); loss of rows of close-set setulae from the tarsi; some costalization of veins in the wing.

• Internode 7. Adult mouthparts not used for feeding; with reduced chaetotaxy, and clothed with long hairs; thoracic suture complete; calypters enlarged and concealing the halteres; vein M 1 deflected forward at or apicad of cross vein dm-cu; rows of close-set setulae lost from the tarsi; greater ampulla developed; ejaculatory sclerite well formed and detached from aedeagal apodeme; anal cerci of male contiguous or fused below the anus.

Conclusion

What therefore are the bot flies? They are flies that are parasitic in the larval stage in mammals; the TTM has become extremely reduced. The group originated from basal ephydroids ( Figure 2). Their founding forms would have had well-developed mouthparts, possibly including prestomal teeth in the adult, but the mouthparts have been reduced to a variable extent in two or more lines of descent. The size of the bot flies is medium to large. The reason why the bot flies have for so long been regarded, incorrectly, as Calyptratae is no doubt bound up with these features, namely size and bulky form of the adult fly and larval parasitism on mammals, as well as the calyptrate-like homoplasies to be found in some oestrid subgroups. Insufficient attention to Gasterophilus and Gyrostigma may also have played a part.

Several authorities have regarded gasterophilids as acalyptrates (e.g. van Emden 1944; Rohdendorf 1974) but the case has never before been supported by the extensive comparative anatomical detail given here. Members of Glossinidae – Hippoboscidae have severed their dependence on larval parasitism by the development of full viviparity. Oestrinae (the nasal bots) have moved some way along a parallel path, but in this group, while the developing eggs are retained in a brood pouch, the older larvae have remained parasitic on mammals: probably the loss of functional adult mouthparts for feeding committed oestrine larvae to this parasitic way of life. The oestrine flies present us with a strong hint of the probable protoglossinid life cycle (i.e. a life cycle transitional between the oviparous one and a fully viviparous one), but the protoglossinids would have retained their functional adult mouthparts and the older larvae might possibly have been parasitic on early perissodactyls (see previous section).

The bot flies do not constitute a monophyletic unit: either the term Oestridae could be expanded so as to apply to Glossinidae – Hippoboscidae and all the bot flies, or the term could be contracted to apply only to the non-gasterophilid bot flies (cuterebrines, hypodermatines and oestrines, and the anomalous genera Ruttenia Rodhain , Neocuterebra Grünberg and Cobboldia , that are parasitic on the skin or within the stomach of elephants). Decisions as to the appropriate superfamily, family, subfamily etc. ranking to be applied to the various taxa reviewed here would be taken after agreement as to the lines of descent.

The non-gasterophilid bot fly sub-groups show, by their respective autapomorphies, approaches to what may be called the calyptrate grade of organization. The list of such features includes: enlargement of the calypters; abdominal spiracles set in tergites in many cases; transformation of the fultelliform aedeagal apodeme to a simple rod no longer attached to the hypandrium; drift of sternite 6 in the male abdomen to a left lateral position in many cases ( Grunin 1965); and the anal cerci becoming contiguous or fused below the anus. The different sub-groups have radiated in different ways in these respects. For instance, Hypoderma (Hypodermatinae) retains most abdominal spiracles in the membrane but sternite 6 of the male abdomen is asymmetrically placed ( Patton 1936); Cuterebra fontinella (Cuterebrinae) has retained a symmetrical sternite 6 in the male abdomen but the cerci are contiguous ventral to the anus and pointed ( Patton 1935).

The search for the origin of Glossinidae is inextricably linked to the question of the origin of the bot flies. A critical examination of the comparative anatomical evidence reveals clear links between Glossinidae – Hippoboscidae and the Gasterophilidae , as well as the ephydroid links of the bot flies, most readily detected in the gasterophilids.

The pioneering work by Vossbrinck and Friedman (1989), Gleeson et al. (2000), Nirmala et al. (2001), Otranto and Stevens (2006), Dittmar et al. (2006) and Petersen et al. (2007) on molecular sequence comparisons represents a useful start to the process of assembling a data base from which solid phylogenetic conclusions concerning Glossinidae – Hippoboscidae and the bot flies may eventually be drawn; the effort has to be extended to more genes, and to more taxa especially basal ephydroids. The importance of Cyrtona in this respect has to be emphasized. Some taxonomic and review papers fail to discuss published alternatives to the traditional grouping of Oestridae with the Tachinidae family-group, of Glossinidae – Hippoboscidae with the ectoparasitic bat flies and of the monophyly of Calyptratae. As a result, workers such as geneticists coming fresh to the area, may not be making the most appropriate choice of outgroups for their investigations. Valuable information that might otherwise have been obtained will therefore remain inaccessible.

Unless entirely new data are offered, claims that the bot flies derive from within Tachinidae family-group or indeed Calyptratae should be recognized as being without solid foundation in comparative anatomical terms and abandoned. The removal of Oestridae from Tachinidae family-group will make the remainder of the latter group far more coherent and amenable to phylogenetic analysis, and here Pape’s methodology should bear fruit.