Distinguishing Tachina fera group species

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We now have at least 2 species of the “Tachina fera group”: Tachina fera & Tachina magnicornis, and there is a suspicion that we might also have an unnamed species that has been found in Scandinavia, currently called T.sp.. T.magnicornis was new this year (Hollesley, E.Suffolk, TM34674385; 21.viii.2023; coll: Raymond Watson) and keyed out fairly easily (the male frons was 1.5x the width of the eye and the genitalia matched the images in Novotna, Vanharra et al (2009)) but we need to examine more material to see if we can detect the other species.

From initial discussions, T.fera seem to have paler, brown front tarsi and the male claws will be very long (as long as the last 2 segments together); while T.magnicornis front tarsi should be dark blackish with shorter claws, just longer than the last segment. I’m not sure where “T.sp.” fits but it’s likely to be closer to T.fera than magnicornis.

THE BOTTOM LINE IS – PLEASE DISSECT YOUR MALE “TACHINA FERA” AND CHECK FOR THE TWO OTHER SPECIES!

Here is the key excerpt from the Central European key by Tschorsnig & Herting (1994) – note that it doesn’t include the unnamed species

  • Frons in males 0.68 – 1.08x, in females 0.94 – 1.28x as wide as one eye. Fore tarsus yellow, seldom brown. The black longitudinal abdominal stripe ends almost always in a tip on tergite 5. Males: anterior claws almost as long as the last 2 tarsal segments combined (fig. 146); frons as a rule without oe, seldom 1 oe present =fera L.
  • Frons in males 1.10 – 1.39x, in females 1.27 – 1.55x as wide as one eye. Fore tarsus brown or black. Males: anterior claws clearly shorter than the last 2 tarsal segments combined; frons with 1 or 2 oe
    • The black longitudinal abdominal stripe widens towards the end on tergite 5, seldom ending in a point. Males: anterior claws longer than the last tarsal segment. Females: 4th segment of the fore tarsus clearly wider than long =magnicornis Zett.
    • The black longitudinal abdominal stripe ends in a tip on tergite 5. Males: anterior claws at most as long as the last tarsal segment. Females: 4th segment of the fore tarsus at most as wide as long =nupta Rond.

In 1994 T&H commented here that “Taking into account the large spread of variability as regards the abdominal patterning and anterior claw length in magnicornis, it is not impossible that nupta may not be an individual species, but only a form of magnicornis“. So even then there was the feeling that nupta would be possibly lumped in with magnicornis but the 2009 paper did the opposite by confirming nupta as a valid species AND then including an unnamed species. In 2010 Cerretti synonymised nupta under magnicornis. Christer Bergström has also been using the name T.tetramera to refer to species between fera & magnicornis and he has his own key for Scandinavian species which I hope to refer to later.

Here are some excerpts from Novotna, Vanharra et al (2009)

Legend: Bph=basiphallus; Bs=bacilliform sclerite; Ca=callus of syncercus; Dph=distiphallus; E(T9)=epandrium (tergite 9), Ea=ejaculatory apodeme, Ha=hypandrial arm; Hcp=hypandrial central plate, Hy=hypandrium; Ms=medial stripe of distiphallus; Pha=phallapodeme; Pl=posterior lobe of sternite 5; Postg=postgonite; Preg=pregonite; Rg=ridge of sytncercus, Sps=spine of syncercus, Sp 6=spiracle 6; Sp 7=spiracle 7; Sts 7+8=sternite 7+8 (=syntergosternite 7+8); Sur=surstylus; Syn=syncercus; S5=sternite 5; S6=sternite 6.

  • 3.3.4. Tachina (Eudoromyia) fera (Linnaeus, 1761); (Fig. 7)
    • Syncercus in caudal view relatively stout and long, gradually tapered towards tip; distinctly reaching beyond surstyli; submedial dilation (callus) inconspicuous; apical part beyond callus stout and notable (sic) broad at base; in lateral view with a distinct dorsal (outer) callus; ventral margin without a distinct emargination next to apical spine.
    • Surstylus in caudal view with a relatively shallow and wide lateral (outer) incision; apical lobe with a slender projection at tip as in T.sp.
    • Bacilliform sclerite with upper distal projection with a narrowly tapering but rounded tip as in other species of the subgenus Eudoromyia.
    • (Fig. 7):
Tachina fera
  • 3.3.5. Tachina (Eudoromyia) magnicornis (Zetterstedt, 1844); (Fig. 8)
    • Syncercus in caudal view relatively long and gradually tapered towards apex, conspicuously reaching beyond level of lower margin of epandrium; in lateral view with an indistinct dorsal (outer) callus; ventral margin with a concave emargination at about middle and distinctly emarginate next to the apical spine.
    • Surstylus in caudal view with a deep angular lateral (outer) incision; apical lobe stout and abruptly tapered into a short and slender tip. surstyylus not reaching beyond lower margin of epandrium.
    • Baciliform sclerite with upper projection slender and long, rod-like and rounded apically.
    • (Fig. 8):
Tachina magnicornis
  • 3.3.7. Tachina (Eudoromyia) sp.; (Fig. 11) (aka tetramera)
    • Syncercus in caudal view distinctly dilated directly beyond callus but then gradually narrowing towards the apical spine, extending beyond apices of surstyli; in lateral view relatively slender with the somewhat broadened basal part ocupying nearly 2/3 of its length, callus rather prominent but less so compared with T.fera; apically (narrow) part more slender than in T.fera; basal part separated from distal part by rather shallow emargination about middle and also with a distinct emargination next to apical spine.
    • Surstylus in caudal view with an angular and deep lateral (outer) incision graduallly tapered towards tip, apical lobe relatively long and slender.
    • Bacilliform sclerite with upper projection slender, finger-like and rounded apically.
    • (Fig. 11):
Tachina sp. (tetramera)

Some photos of the first T.magnicornis

male genitalia
bacilliform sclerites inside the genital capsule
tip of surstylus
tip of syncercus

The photos show the importance of hooking out the male genitalia completely and making sure the syncercus is fully visible – it isn’t very well done in the above example but it is visible if you manipulate it.

Summary of the most useful identification features

  • T.magnicornis is easy in that the frons width is a really good feature and the male genitalia are quite distinctive too, with a long thin syncercus with no callus.
  • T.fera has the narrow frons and a fatter syncercus with a strong callus (a hump on the back).
  • T.sp. is a bit of a mystery because I haven’t managed to find any yet so I am not able to comment on the general morphology but it seems that it is closest to T.fera so might look like like that. The genitalia certainly seem to be closest to that species but it might be that genitalia is the only way to split them if this species is found here.
  • The surstylus incision and apical lobe shape needs to be checked some more but it also looks useful.

References

  • Cerretti, P. (2010) I Tachinidi della fauna Italiana (Diptera Tachinidae): con chiave interattiva dei generi ovest-paleartici.
  • Novotna, Vanharra et al (2009) Identification and taxonomy of the West Palaearctic species of Tachina Meigen (Diptera: Tachinidae) based on male terminalia and molecular analyses.
  • Tschorsnig, H.-P. & Herting, B. (1994) Die Raupenfliegen (Diptera: Tachinidae) Mitteleuropas: Bestimmungsta-bellen und Angaben zur Verbreitung und Ökologie dereinzelnen Arten. – Stuttgarter Beiträge zur Naturkun-de, Serie A (Biologie) 506. 170 pp. – English translation by R. Rayner & C. Raper, authorized by H.-P.Tschorsnig. [www document]. URL https://tachinidae.org.uk/blog/downloads/. (last checked October 2023)

Published by ChrisR