@Prohercostomus@, a New Subgenus of the Genus @Hercostomus@ Loew

(Diptera, Dolichopodidae) from Baltic Amber

I. Ya. Grichanov

All-Russian Research Institute of Plant Protection, Russian Academy of

Agricultural Sciences, Podbelskogo 3, Pushkin, St. Petersburg, 189620

@Abstract---A new subgenus of @Hercostomus@ Loew, @Prohercostomus@

subgen. nov. (Diptera, Dolichopodidae), is described for @Dolichopus

noxialis@ Meunier (type species; redescribed) and 6 other species, all

from Baltic amber. Subgenera of @Hercostomus@ are keyed.

Received July 1, 1996

INTRODUCTION

Paleogene fauna of dolichopodid flies from Baltic amber is quite rich

but nevertheless rather poorly studied (Keilbach, 1982; Spahr, 1985).

The last monographic treatment of this fauna appeared in the beginning

of our century (Meunier, 1907, 1908a, b). Systematics of the family

considerably changed since. Very short species descriptions given by

Meunier often do not allow to determine even the generic position of

these taxa correctly. Some species were probably misplaced by him at

generic level, as already suggested by Negrobov (1978) for those which

were assigned by Meunier to the genus @Dolichopus@ Latreille, 1796.

Therefore a revision of this type material is urgently needed.

Unfortunately the present location of the type collection, which was

kept in the former Geologisch-Pal@aontologisches Institut, Universit@at

K@onigsberg, is unknown.

RESULTS AND DISCUSSION

A piece of Baltic amber purchased by me in Vilnius contains a male of

dolichopodid, doubtless belonging to the extant genus @Hercostomus@

Loew, 1857. This find confirms an opinion (Bickel, 1994) that recent

genera of Dolichopodidae have already appeared in the Paleogene.

Comparison of this specimen with the descriptions made by Meunier allows

to assign it to @Dolichopus noxialis@; his quite accurate drawings of

the antenna and fore and hind tarsus nearly exclude erroneous

identification. Related species described by Meunier under the genera

@Gymnopternus@ Loew, 1857 and @Dolichopus@ should be transferred to

@Hercostomus@ as well.

Recent fauna of the genus @Hercostomus@ comprises about 320 mostly

Holarctic species (Foote et al., 1965; Negrobov, 1991). Known tropical

species of this group will be probably excluded from the genus after

future revision (Robinson, 1970; Dyte, 1975). The taxonomy within the

genus turned out to be rather complicate, and in recent papers it is

usually divided into the subgenera @Hercostomus@ s. s., @Gymnopternus@

Loew, 1857, @Platyopsis@ Parent, 1929, and @Poecilobothrus@ Mik, 1878

(Pollet, 1990; Negrobov, 1991). Besides that, Stackelberg (1949) created

one more subgenus, @Microhercostomus@, for @Hercostomus dilatitarsis@

Stackelberg, 1949 from Kondara Gorge (Gissar Range, Tadzhikistan). The

only type specimen differs from all the other @Hercostomus@ species by

the absence of posterior crossvein (@m-cu@[ITAL]) in the wings. A

representative series collected by the author of this paper in 1979 in the

canyon of Varzob River, the type locality of this species (5 males and 5

females; Gissar Range, Takob Gorge, 1800 m; in collection of Voronezh

University). All the specimens are identical to the holotype except for

retaining @m-cu@ crossvein. Its absence is obviously an exception

(mutation), very rare in the subfamily Dolichopodinae. Therefore the

subgenus @Microhercostomus@ Stackelberg is considered a synonyme of the

nominative subgenus, @Hercostomus@ s. s.

A careful examination of @H. noxialis@ had shown that it could be

included into neither extant subgenus of @Hercostomus@. The species

combines the characters diagnostic for some of extant subgenera with

several obvious plesiomorphies, permitting to describe a new subgenus of

@Hercostomus@. The most characteristic of its plesiomorphies are the

unusual leg chaetotaxy, elongate R@1 vein, simple massive surstyli and

gonopods of males, etc. As judged from the habitus, this new subgenus

could be ancestral group to the others (except for @Poecilobothrus@).

The diagnosis of a new subgenus, a key to subgenera of @Hercostomus@,

and the detailed redescription of @H. noxialis@ are given below.

SYSTEMATIC PALEONTOLOGY

@Prohercostomus@ subgen. nov.

@Type species. @Dolichopus noxialis@ Meunier, 1907; Baltic amber.

@Diagnosis. Head with single pair of stout ocellar bristles. Postocular

setae black, numerous. Face narrow. Pubescense of arista undeveloped.

Thorax with single stout propleural bristle. Humeral tubercle with one

stout and several short bristles. Six dorsocentral bristles. Acrostichal

bristles in two series reaching fifth pair of dorsocentral bristles.

Posterior part of mesoscutum without dark hairs. Scutellum with two

stout bristles and two hairs on sides. Legs simple. Fore and middle

coxae with small hairs and several bristles in distal half, hind coxae

with single stout bristle. Middle and hind femora with single, stout but

short, anterior subapical bristle. Tibial bristles poorly developed,

scarcely as long as diameter of tibia; ventral bristles undeveloped;

dorsal bristles on fore and hind tibiae forming single series along

their whole length. Wing elliptical, about twice as long as wide; R@1

reaching wing midlength; R@4+5 and M@1+2 in distal wing half parallel;

anal lobe broad; alula undeveloped. Abdomen (including 8th segment) in

dark bristles. Hypopygium not large, without stalk; cerci simple;

surstyli and gonopods large, massive, relatively simple.

@Composition. Subgenus @Prohercostomus@ comprises following species (all

from Baltic amber):

@bickeli@ Evenhuis, 1994: 361 (@Dolichopus@), comb. nov.;

= @vulgaris@ Meunier, 1907: 221 (@Dolichopus@), comb. nov.;

@interceptus@ Meunier, 1907: 221 (@Gymnopternus@), comb. nov.;

@intremulus@ Meunier, 1907: 221 (@Gymnopternus@), comb. nov.;

@meunierianus@ Evenhuis, 1994: 361 (@Dolichopus@), comb. nov.;

= @notabilis@ Meunier, 1907: 221(@Dolichopus@), comb. nov.;

@monotonus@ Meunier, 1907: 221 (@Dolichopus@), comb. nov.;

@negotiosus@ Meunier, 1907: 221 (@Dolichopus@), comb. nov.;

@noxialis@ Meunier, 1907: 221 (@Dolichopus@), comb. nov.;

Key to subgenera of @Hercostomus@

1. Arista with pubescense long (about 1.5 times as long as basal width

of arista); distinct purple spot in notopleural pit; male cerci elongate

triangular with ventral margin strongly incised .................

@Poecilobothrus@

- Arista bare or rarely pilose; notopleural pit normally without purple

spot; cerci variously shaped ....................... 2

2. Face broad, parallel-sided; epistome concave, clypeus convex; palps

relatively large and wide; first metatarsomere with single ventral

bristle ........ @Platyopsis@

- Face at least in male relatively narrow; clypeus not or at most

weakly convex; palps normally small, rarely large and elongate; first

metatarsomere without stout ventral bristle ....... 3

3. Tibial bristles poorly developed, scarcely as long as diameter of

tibia; ventral bristles undeveloped; dorsal bristles on fore and hind

tibiae forming single series along their whole length; R@1 reaching wing

midlength; male surstyli and gonopods massive, simple ........

@Prohercostomus@ subgen. nov.

- Tibial bristles (including ventral ones) usually well-developed;

dorsal bristles at least in basal half of fore and hind tibiae divided

into anterodorsal and posterodorsal; R@1 usually not reaching first

third of wing length; male surstyli and gonopods complicately shaped,

often slender ........... 4

4. Metapleuron with group of hairs before posterior spiracle; mesoscutum

posteriorly and scutellum dorsally hairy; R@4+5 and M@1+2 parallel

............. @Gymnopternus@

- Metapleuron and posterior mesoscutum usually bare; scutellum usually

with two stout bristles and two marginal hairs; R@4+5 and M@1+2 usually

converging ............. @Hercostomus@ s.s. (@Microhercostomus@, syn.

nov.)

@Hercostomus (Prohercostomus) noxialis@ (Meunier, 1907)

@Dolichopus noxialis@ Meunier, 1907: 221, 1908a: 46, 1908b: 88, 1912:

179; Keilbach, 1982: 375; Spahr, 1985: 34; Evenhuis, 1994: 362.

@Types. In the collection of former Geologisch-Pal@aontologisches

Institut, Universit@at K@onigsberg (location unknown).

@Description (Fig. 1). General coloration of the head, thorax and

abdomen is dark, with metallic shine, at certain illumination shot with

green. Pollinosity and minute pale hairs are virtually

indistinguishable. Face is narrow (ratio of its width below antennae to

height 8 : 27); clypeus is not convex, twice narrower than epistome.

Antenna is entirely dark, with 2nd segment rounded and 3rd segment

elongate triangular (twice as long as high), apically acuminate; arista

lacks distinguishable pubescense, consists of two segments, and

originates in distal third of 3rd segment. Ratio of the lengths of 1st

to 3rd antennal segments to the height of 3rd segment and lengths of 1st

and 2nd segments of arista is 5 : 4 : 13 : 7 : 7 : 30.

Legs are mostly pale, except for dark middle and hind coxae, hind tibiae

in distal half, fore and middle tarsi (except for the base of first

segment), and hind tarsi. All legs are simple, with short black bristles

scarcely exceeding in length the diameter of the respective podomeres.

Fore and middle coxae are covered with small hairs, with several

bristles in distal half. Hind coxae bear a single stout outer bristle.

Middle and hind trochanters bear a single stout dorsal bristle. Fore

femora bear one to three posteroventral subapical hairs. Fore tibiae

bear a series of 10 short but stout dorsal bristles along their whole

length, with elongate anteroventral bare area in distal half; other

bristles are lacking. 1st segment of the fore tarsi bears a ventral

series of very short, scarcely visible spinules. Middle femora bear a

single, short but stout, anterior subapical bristle and several

posteroventral subapical hairs. Middle tibiae bear two anterodorsal, two

to three posterodorsal, and five to six apical bristles. Hind femora

bear one short but stout, anterior subapical bristle, several

posteroventral subapical hairs, and a series of short but distinct,

dorsal hairs in basal half. Hind tibiae bear a series of 12 short dorsal

bristles along their whole length, and several very short apical

bristles. Ratio of the lengths of coxa, femur, tibia, and 1st to 5th

tarsomeres is for the fore legs 35 : 52 : 45 : 27 : 13 : 10 : 6 : 6, for

the middle legs 27 : 55 : 57 : 28 : 15 : 12 : 9 : 8, and for the hind

legs 20 : 65 : 63 : 70 : 25 : 15 : 10 : 9.

Wings are elliptical and lack spots. Costal vein lacks thickenings. R@1

reaches wing midlength. R@2+3 is nearly straight. Ratio of the section

of costal vein between R@2+3 and R@4+5 to its section between R@4+5 and

M@1+2 is 23 : 14. R@4+5 and M@1+2 are parallel in distal wing half and

both slightly curved towards posterior wing margin. M@1+2 joins costal

vein a little beyond wing tip. Ratio of the proximal and distal sections

of M@1+2 is 65 : 71. Crossvein @m-cu@[ITAL] is slightly convex and forms

right angles to both longitudinal veins. CuA@1 reaches the wing margin.

Ratio of the proximal and distal sections of CuA@1 to @m-cu@ is 65 : 34

: 16. Anal vein ends not reaching the wing margin; anal angle is right.

Calypters are poorly distinguishable, pale (?) with dark (?) setae.

Halter is pale.

Abdomen bears dark bristles, dorsally and laterally the short ones,

ventrally (on 2nd to 4th sterna) the long ones. 8th segment bears stout

dark bristles. Hypopygium with appendages is dark, shorter than the

length of 4th--6th abdominal segments combined. Epandrium bears very

short and dense erect hairs dorsobasally. Cerci are flat, elongate oval,

with narrow apex, densely beset with long dark bristles. Surstyli are

elongate triangular, massive, a little shorter than cerci, with a small

ventrobasal lobe; their apices are weakly curved ventrad and bear at

least two small bristles. Gonopods are long, massive, curved dorsad,

slightly widened at apex, with an apical hair as long as surstyli.

Hypandrium and the bases of gonopods are concealed by the last abdominal

segments.

@Measurements (mm): body length 2.6, length of wing 2.5, length of

hypopygium 0.6.

@Comparison. @H. (P.) noxialis@ is clearly distinct from other species of

the subgenus described by Meunier in the shape of 3rd antennal segment

(1st flagellomere) and ratio of tarsomeres. In the ratio of length and

height of 3rd antennal segment this species is most similar to @H. (P.)

meunierianus@, being distinct from the latter in the arista originating

in distal third of 3rd segment, and in the 1st segment of fore tarsi

being twice longer than the 2nd one.

@Remarks. The difference between yellow, orange, brown, and purple

colors, which are quite widely used in diagnostics of the recent species

of @Hercostomus@, is masked by coloration of the amber.

@Material. Completely preserved male in the piece of Baltic amber

labelled: Baltic Amber: Vilnius, 13.04.1996, I.Y. Grichanov (in author's

collection); Upper Eocene--Lower Oligocene.

REFERENCES

Dyte, C.E., Family Dolichopodidae, in @A Catalog of the Diptera of the

Oriental Region@, Honolulu: Univ. Haw. Press, 1975, vol. 2, pp. 212--

258.

Evenhuis, N.L., @Catalogue of the Fossil Flies of the World (Insecta:

Diptera)@, Leiden: Backhuys, 1994.

Foote, R.H., Coulson, J.R., Robinson, H., Family Dolichopodidae, in @A

Catalog of the Diptera of America North of Mexico@, U. S. Dept. Agric.,

Agricult. Handb., 1965, no. 276, pp. 482--530.

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Meunier, F., Monographie des Dolichopodidae de l'ambre de la Baltique,

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233--235, 245--246, 260--262, 269--271, 281--282.

Meunier, F., Monographie des Dolichopodidae de l'ambre de la Baltique,

@Naturaliste@, Paris, 1908a, vol. 30, pp. 7--9, 21--23, 29--30, 45--46,

57--59.

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1--291.

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Spahr, U., Erganzungen und Berichtigungen zu R. Keilbachs Bibliographie

und Liste der Bernsteinfossilien -- Ordnung Diptera, @Stuttgarter Beitr.

Naturk.@, 1985, B, no. 111, pp. 1--146.

Stackelberg, A.A., Species of the Genus @Hercostomus@ Lw. (Diptera,

Dolichopodidae) of Middle Asiatic Fauna, @Tr. Zool. Inst. Akad. Nauk

SSSR@ (Leningrad), 1949, vol. 8, no. 4, pp. 669--687.

Figure caption

Fig. 1. @Hercostomus (Prohercostomus) noxialis@, hypopygium in right

lateral view.