Merothrips dietrichi (Schliephake) Schliephake, 2017

Ulitzka, Manfred R. & Mound, Laurence, 2017, The fossil species Merothrips dietrichi (Schliephake) comb. n. redescribed and transferred from the genus Heterothrips (Thysanoptera), Zootaxa 4231 (4), pp. 573-576 : 574-575

Merothrips dietrichi (Schliephake) comb.n.

Heterothrips dietrichi Schliephake, 2003: 179 .

Holotype female, inclusion in Baltic Eocene amber, found in a gravel pit near Sarstedt (Lower Saxony, Germany). Collection Ulitzka No. MU-Fos-44/1.

Description. Colour of body, head, legs and antennae uniformly light brown ( Fig. 1 ).

Measurements (holotype female, in microns). Body length 832 (slightly contracted). Head, length 104; width 127. Eyes, length 44. Interocellar setae 64; postocular setae 16. Pronotum, length 120; basal width 135; anteroangular setae 20; anteromarginal setae 13; posteroangular setae 23; posteromarginal setae 14. Mesonotum, length 45; width 122. Metanotum not measurable due to the position of the wings. Mesothorax, largest width measured over the spiracles 173. Abdomen, length 430 (measured ventrally); largest width (segment V) 237; setae on tergite IX S1 134, S2 192, S3 96; axial setae of the trichobothria on tergite X 143, diameter of their sensoria 4. Antennae, length 256; length (width) of antennomeres I 20 (26), II 29 (23), III 39 (16), IV 42 (16), V 29 (14), VI 29 (13) VII 29 (13), VIII 39 (10). Fore wings, length 576; width in the middle 38. Fore tibiae (difficult to measure) about 78; dorsal seta 75. Middle tibiae 78; dorsal seta measurable only at the left, tip broken off at a length of 48. Hind tibiae 105; dorsal seta (hardly visible) about 70.

Head ( Figs 1, 2 ). Wider than long, weakly sculptured on posterior half, produced in front of the compound eyes; with one pair of long ocellar setae arising outside the ocellar triangle (missing on the left) and one pair of major postocular setae lying well behind the eyes. Eyes not distended ventrally. Antennae with eight antennomeres (not nine, as mentioned in Schliephake [2003]); all segments clearly distinct from each other and bearing long setae; segments III and IV each with a transverse oval sensorium on apex (cf. Schliephake 2003, fig. 1).

Thorax. Prothorax ( Figs 1, 2 ) longer than wide, slightly trapezoidal, with a pair of conspicuously curved longitudinal sutures laterally. Pronotum smooth, without any lines of sculpture; bearing one pair of anteroangular setae, one pair of anteromarginal setae arising well behind the anterior margin, one pair of posteroangular setae and three pairs of posteromarginal setae. Mesothorax much wider than prothorax, weakly sculptured. Fore wings narrow, with two longitudinal veins lying close together; first vein with a row of about 19, second vein with 16 setae (median setae are difficult to count due to reflections in the amber); wing surface without microtrichia; fringes straight; wing scale with a single seta distally. All tibiae bearing dorsally one long median seta; fore tibiae with a slender tubercle at inner apex (due to position of the legs difficult to assess). Tarsi with two tarsomeres; basal tarsomere of fore tarsi bearing one long apical seta on outer margin.

Abdomen. Tergites with transverse lines of sculpture; tergites IX and X with long setae; tergite X additionally with a pair of trichobothria, each bearing a conspicuously long axial seta. Sternites with faint lines of transverse sculpture, without discal setae; sternite VIII reduced to a pair of lobes on posterior margin of seventh sternite ( Fig. 3 ), each lobe bearing two setae. Ovipositor reduced; hidden in the body, visible only at extreme tip.

Comments. This is the fourth species of Merothripidae found in Baltic Amber, and the third species of fossil Merothrips from the Tertiary Eocene. The original specimen of M. fritschi was lost during the Second World War, but the description by Priesner (1924) provides sufficient detail to distinguish it from dietrichi . The body of M. fritschi is longer and more slender but with conspicuously shorter antennae. The length and width of the head of fritschi are almost equal, but in dietrichi the head is much wider than long. Like most extant Merothrips species, the hind margin of the pronotum of fritschi and dietrichi bears only one pair of posteroangular setae, but these setae differ in length. The head of balticus is also longer than wide, but the body is similar in shape to that of dietrichi , although balticus bears two pairs of pronotal posteroangular setae, similar to the extant species M. mirus ( Mound & O’Neill 1974) .

Figures

FIGURES 1 – 3. Merothrips dietrichi, female. (1) dorsal view; (2) head, prothorax and left fore leg; (3) abdominal sternites VI – X.