Lestremia eocenica, Nel & Prokop, 2006

Nel, André & Prokop, Jakub, 2006, New fossil gall midges from the earliest Eocene French amber (Insecta, Diptera, Cecidomyiidae), Geodiversitas 28 (1), pp. 37-54 : 38-41

Lestremia eocenica n. sp. ( Fig. 1 )

TYPE MATERIAL. — Holotype specimen PA 5314 1/2 (male), paratypes PA 3296, PA 2540, PA 1303, PA 5135, PA 8106 1/5, PA 157 1/3 (males).

ETYMOLOGY. — After the Eocene age of the fossils.

DIAGNOSIS. — Male flagellomeres with nodes four times as long as necks; palpal segment 4 just slightly longer than third; male gonostylus large and broad, divided into a large side lobe and an apical lobe, both with apical macrosetae.

DESCRIPTION

Head 0.11 mm long, 0.23 mm wide, 0.32 mm high; eyes very broad, nearly meeting below antennae; eye bridge complete and long; two ocelli well developed just above the eyes; antenna 0.81 mm long, scape 0.01 mm long, 0.02 mm wide, pedicel 0.04 mm long, 0.03 mm wide, 14 long flagellomeres of nearly the same size, all longer than wide (0.05 mm long, 0.03 mm wide), and with distinct neck, but flagellomere nodes distinctly longer than necks (ratio length of node/length of neck 0.25), last flagellomere 0.06 mm long; flagellomeres with three rows of setae, the two basal ones being crenulate; digitate sensoria absent on flagellomeres; gena short; palpus very long, 0.28 mm long, with four long segments visible, with palpal segment 1 short and stout, distal three palpal segments elongate, palpal segment 2 0.1 mm long, palpal segment 3 0.11 mm long, palpal segment 4 0.12 mm long; presence of rather long setae on palpal segments 3 and 4.

Thorax 0.34 mm long, 0.20 mm high, 0.29 mm wide, longer than broad.

Wing 1.14 mm long, 0.44 mm wide, hyaline, with microtrichia and macrotrichia, especially in posterior part of wing and along posterior margin; veins of posterior part of wing sclerotized but less than those of anterior part; Costa not ending at apex of R5 but continuing around wing, although the strong anterior portion of C ends up with R5; humeral vein present, 0.13 mm from wing base; subcostal vein incomplete, 0.34 mm long, not reaching wing margin; vein R1 short, reaching anterior wing margin 0.23 mm basal of apex of Rs; vein Rs 0.16 mm long, emerging from R close to apex of R1 (0.32 mm basal of apex of R1); cross-vein r-m present but very short, 0.08 mm long; sector of M1+2 basal of fork into M1 and M2 0.36 mm long, distinctly shorter than branches of fork; M1 complete and curved basally; M2 complete basally; vein m-m absent; vein M3+4 distinct, simple and nearly straight, basally vanishing close to M (visible in specimen PA 5314 1/2) but basally replaced by a fold (visible in other specimens), very close to base of M; CuA simple, curved; CuP present, parallel to CuA and 0.38 mm long; A1 curved and long, complete basally and ending close to posterior wing margin; A2 not visible, probably absent.

Haltere with large knob, 0.05 mm wide and 0.11 mm long, and stem 0.05 mm long, bearing only two setae at its apex.

Legs slender, without scales; fore femur 0.41 mm long, tibia 0.44 mm long, tarsi 0.57 mm long; mid femur 0.43 mm long, tibia 0.46 mm long, tarsi 0.60 mm long; hind femur 0.44 mm long, tibia 0.46 mm long, tarsi 0.61 mm long; femora and tibiae not especially swollen; tibial spurs absent; tarsal claw with basal lobe with small teeth; all legs with five tarsomeres, with tarsomere 1 longer than 2.

Abdomen (male) with eight segments before genitalia, 0.63 mm long, 0.26 mm wide, bearing numerous long setae; segment 8 unmodified; parameres very narrow in distal portion; gonocoxites bearing numerous setae; gonostylus large and broad, 0.18 mm long, 0.10 mm wide, bilobed, with main lobe cylindrical and bearing three to four short megasetae, with side lobe directed inwards, terminating in a long megasetae.

DISCUSSION

Following the key to dipteran families of McAlpine (1981), L. eocenica n. sp. falls in the Cecidomyiidae Lestremiinae because of the following characters: vein A2 absent, R with only two branches, C continuing around wing, first tarsomere longer than second, each tarsus five-segmented, two ocelli present (although some Lestremiinae have no ocelli, see Gagné 1995). After Wood & Borkent (1986, 1989), L. eocenica n. sp. falls in the Cecidomyiidae rather than in Sciaridae , because of the following synapomorphies:presence of an eye bridge (character also present in Sciaridae and Scatopsoidea), tibial spurs absent (see also Gagné 1994) (but character also present in Scatopsidae ); setae of flagellomeres arranged in encircling whorls.

Gagné (1994) proposed a phylogeny of the Cecidomyiidae , with the Lestremiinae as sister group of all other representatives of the family, but without giving any synapomorphy supporting the clade Lestremiinae . Jaschhof (2000) proposed to consider the Catotrichinae as most basal clade and the Lestremiinae as sister group of the Porricondylinae + Cecidomyiinae , supporting the monophyly of the Lestremiinae by the presence of crenellate whorls in male flagellomeres. L. eocenica n. sp. has two crenellate whorls of long setae, longer than the width of the flagellomere. Thus, we place L. eocenica n. sp. in the Lestremiinae .

Following the keys to Nearctic and European genera proposed in Gagné (1981, 1994) and Skuhravá (1997), L. eocenica n. sp. falls in the Lestremiinae Lestremiini because of the following characters:only two ocelli present, tarsi five-segmented, metatarsus distinctly longer than second tarsal segment, M1+2 present, with its fork longer than its stem, legs without scales, macropterous, CuA simple, M3+4 distinct, R5 more than two-thirds length of wing, 14 (more than six) flagellomeres, each longer than wide, tibiae without disto-ventral spines, Rs shorter than r-m. Jaschhof (1998: fig. 236, characters 7, 8) characterized the Lestremiini after the relative sizes of the scape, pedicel, and flagellomeres. L. eocenica n. sp. has a broad and large scape and pedicel, distinctly broader than its flagellomeres.

According to Jaschhof (1998: fig. 237), the phylogeny of the Lestremiini is imperfectly understood. Nevertheless, the genera Anarete Haliday, 1833 and Conarete Pritchard, 1951 can be excluded because of the presence of 14 long-necked flagellomeres, instead of six to eight with short or indistinct stems. Within the Palaearctic and Nearctic faunas, the presence of two crenellate whorls on flagellomeres excludes affinities with genera other than Lestremia Macquart, 1826 and Anaretella Enderlein, 1911 ( Gagné 1981; Skuhravá 1997). The absence of digitate flagellomere sensoria (also excluding affinities with Allaretella Meyer & Spungis, 1994 ), the parameres very narrow in distal portion, together with M3+4 with proximal end close to M, well before level of r-m, exclude the genus Anaretella and are characters diagnostic of recent Lestremia ( Edwards 1938a; Meyer & Spungis 1994; Skuhravá 1997; Jaschhof 1998).

After Mani (1935, 1945), the Indian genus Neolestremia Mani, 1935 (two species N. boerhaaviae Mani, 1935 and N. longipalpsa Deshpande, Shaikh & Sharma, 2002 ) has a three-segmented palpus, instead of a four-segmented palpus in Lestremia and in L. eocenica n. sp.

L. eocenica n. sp. differs from the recent Lestremia species in the longer flagellomere nodes that are four times as long as the necks, instead of being shorter or of the same length or nearly so ( Kieffer 1913; Jaschhof 1998). This is especially the case for the male flagellomeres in recent species. But this character can be variable as the necks can be very short in the female flagellomeres of the recent L. cinerea Macquart, 1826 (see Jaschhof 1998: fig. 26G). Nevertheless, L. eocenica n. sp. is characterized by its forked gonostylus, unlike the recent Palaearctic Lestremia species. The shape of the bilobed gonostylus of L. eocenica n. sp. is very close to that of Insulestremia sinclairi Jaschhof, 2005 (Galapagos Islands), with a side lobe slightly narrower than that of the latter ( Jaschhof 2005: fig. 2). L. eocenica n. sp. does not present the main character of Insulestremia , i.e. presence of flattened sensillae on the antennal flagellum.

We provisionally include L. eocenica n. sp. in the genus Lestremia , but this attribution needs confirmation after a global phylogenetic revision of the world Lestremiini .

Note: if the Lestremiinae are relatively well known in the Oriental, Palaearctic, and Nearctic regions, it is not the case for the Neotropical and Afrotropical faunas, especially for Africa ( Harris 1980). Thus, it is not possible to propose any biogeographical inference after the present discovery.

COMPARISON WITH OTHER FOSSIL LESTREMIINI Lestremia pinites Meunier, 1904 from the late Eocene Baltic amber is the only known fossil attributed to

Lestremia ( Spahr 1985; Evenhuis 1994). It differs from L. eocenica n. sp. in its long necks of flagellomeres and the relative length of its palpal segments ( Meunier 1904: 31, pl. 3, figs 3, 5). Nothing is known on the male genitalia of L. pinites .

The fossil genus and species Lithomyza condita Scudder, 1877 (lacustrine Green River Formation, middle Eocene, Chagrin Valley, Colorado, USA) is considered as a “Lestreminariae” (= Lestremiini ) by Felt (1911), but with affinities with the genera Microcerata Felt, 1908 (junior synonym of the Lestremini Anarete Haliday, 1833 , after Pritchard 1951), and Tritozyga Loew, 1862 (Catochini) . This fossil would need a revision. Nevertheless, it has nine jointed antennae, unlike L. eocenica n. sp. ( Scudder 1877; Felt 1911).

Figures

FIG. 1. — Lestremia eocenica n. sp., general habitus:A, holotype (PA 5314 1/2), drawing; B, same specimen, photograph;C, paratype (PA 2540), drawing. Scale bars: A, B, 1 mm; C, 0.5 mm.