Thripidae

Ulitzka, Manfred R., 2020, Two fossil thrips from Ethiopian amber (Thysanoptera) with description of Merothrips aithiopicus sp. n. (Thysanoptera: Merothripidae), Zootaxa 4786 (2), pp. 283-288 : 285

Thripidae , cf. Scirtothrips Shull ( Figs 5–7 )

Second instar larva, female. Body dorsoventrally compressed and considerably shrunk after the fossil resin had hardened. Thus, the former shape has left an imprint, which partly shows finest structures. Due to this process, the right side of the thorax was detached from the amber, and the right legs were torn off the body (fig. 5). Body sculptured with scattered tiny round plaques with minute, barely visible microtrichia (fig. 4). Colour: uniformly pale brownish.

Head retracted under pronotum and deformed, hardly any structures recognizable except stemmata on the left side and short, apically expanded d3 setae; mouth cone short and rounded. Antennae 7-segmented (fig. 7); segments III and IV annulated with rings of microtrichia; V short (about one fifth as long as IV); at least one inner sense cone present on segments III, IV and VI. Thoracic features barely assessable; prothoracic setae short and expanded (only two setae visible). Many abdominal features clearly visible in the imprint; tergites with dorsal setae short, these setae slightly longer on IX, d2 blunt to slightly expanded; VIII and IX without campaniform sensilla; segment IX with 5 pairs of setae (fig. 6), without posteromarginal teeth. Spiracles on abdominal segments II and VIII most likely not developed.

Measurements. Second instar larva, female NHMW, N6967a; in microns (all measures refer to the imprint, not to the shrunken body): Body length 902. Head, length including mouth cone 106; width 84; head seta d3 9. Thorax, length about 275; largest width (at metathorax) 180. Prothoracic setae 6. Abdomen, length 525; largest width 366; segment XI, setae d1 12, d2 10, d3 7. Antennae, length 120; length (largest width) of segment I about 10 (19), II 14 (14), III 34 (17), IV 36 (17), V 7 (6), VI 7 (4), VII 12 (4).

Specimen studied. Second instar larva, female; fossil from Ethiopian amber collected near Alem-Ketema , Ethiopia (10°08’45’’N, 38°57’56’’E), see also Schmidt et al. (2010). Stored in the collection of the Naturhistorisches Museum Wien, Vienna, Austria; NHMW, N6967 a.

Syninclusions: lawns of spherical bacteria, plant detritus and stellate plant trichomes, a nematode as well as remnants of different insects (two Coleopteran fragments, legs of an undetermined Diptera, one Mymaridae ).

Diagnosis. Due to the conspicuously short antennal segment V the larva is clearly attributable to Thripidae (fig. 7). Larvae of this family can be distinguished from those of other thrips in having antennal segment V shorter than one-half of the length of IV ( Vance 1974, Vierbergen et al. 2010). Furthermore, it is a second stage larva and a female, because abdominal segment IX bears five pairs of setae ( Vance 1974) (fig. 6). Several other features strongly resemble those of some extant Scirtothrips -larvae, particularly the body sculpture with scattered plaques bearing tiny microtrichia (c.f. Vierbergen et al. 2010, p. 113, figs 83 & 86). This classification might also be supported by the presence of short and apically expanded setae visible at the head and pronotum and, furthermore, by lacking abdominal spiracles. The latter feature, however, is not clearly assessable and these organs—and possibly other characteristics—are possibly concealed by the poor preservation. Thus, the classification at genus level remains rather presumptive and is based on empirical facts.

Figures

FIGURES 1–7. Ethiopian amber fossils. Merothrips aithiopicus sp. n. holotype female 1–4: (1) dorsal view; (2) head, prothorax and metathorax (sa- sensory areas; soc- ocellar setae s3; spo- postocular setae; spa- pronotal posteroangular setae; sco- coxal setae); (3) left fore wing (cross vein indicated); (4) abdominal segments VII–X (spiracles indicated white, trichobothria indicated black).Thripidae, cf. Scirtothrips, female second instar larva 5–7: (5) dorsal view; (6) imprint of caudal abdominal segments (d1–d3- dorsal setae; sl- lateral seta; v1–v2- ventral setae); (7) right antenna.