Helionothrips Bagnall, 1932

Xie, Yanlan, Li, Yajin & Zhang, Hongrui, 2022, The genus Helionothrips (Thysanoptera, Panchaetothripinae) in China, with two new species and an identification key, Zootaxa 5194 (3), pp. 392-402 : 392-398

Helionothrips Bagnall

Helionothrips Bagnall, 1932: 506 .

Type species Heliothrips brunneipennis Bagnall 1915 , by monotypy.

Members of the genus Helionothrips are readily recognised within the subfamily Panchaetothripinae by the following character states: posterior part of head forming a wide transverse concave collar; antennal segments III & IV with curved forked sense cones; abdominal tergites each with a strongly developed antecostal line forming a series of arches or contiguous scallop-like areas. Wilson (1975) has provided a detailed diagnosis of this genus, with a key to the 18 species that were described up to that time. Moreover, reviews have been published of the species known from the following areas: Africa ( Faure 1961), India ( Bhatti 1968), Japan ( Kudô 1992), Taiwan ( Wang 1993) and China (Mirab-balou et al. 2017). Despite these publications some species remain weakly discriminated, being based on descriptions that lack clarity. Here we discuss some characters that can be difficult to evaluate.

Fore wing color. Typically, the fore wings of Helionothrips species are dark brown at the base, with a sub-basal white band and a brown area at the veinal fork, and with the extreme apex also brown. The differences between species are in the colour of the apical half of the wing. This varies from uniformly brown ( annosus , brunneipennis , shennongjiaensis ), gradually fading apically ( cephalicus , communis , linderae , phragmitesi sp.n., ponkikiri , unitatis ), clearly banded ( minutus , rugatus ), to almost pale ( parvus , pallidus sp. n.) ( Figs 1–9 ). It is important to note that “gradually fading apically” involves progressive variation and thus can be difficult to assess. For example, the apical half in aino (and mube ) seems more suitably scored as “uniformly light brown” ( Fig. 4 ), rather than “gradually fading apically” as described in most published literature. Wilson (1975) described the fore wing of cephalicus as “entirely brown except for a subbasal pale patch”, whereas our cephalicus specimens are consistent with “dark brown at fork and fading apicad” as described by Kudô (1992) ( Fig. 6 ). Similarly, Mirab-balou et al. (2017) indicate that the fore wing colour of rugatus is the same as in shennongjiaensis (brown on apical half), but our specimens of rugatus have a well-defined subapical pale band ( Fig. 7 ).

Thorax sculpture. Including one of the new species described below, only four Helionothrips species share the character of “pronotum entirely covered with reticles having numerous wrinkles”. These four are cephalicus ( Fig. 21 ), longisensibilis , pallidus sp. n. ( Fig. 20 ) and rugatus . In contrast, more than 50% of Helionothrips species have all the pronotal reticles without internal wrinkles (e.g. aino , errans , shennongjiaensis ) ( Figs 23, 24 ). Bhatti (1968) described the body sculpture of parvus as “resembling that of errans ”, thus implying that the pronotum of parvus also lacks wrinkles in the reticles. However, Kudô (1992) suggested that cephalicus is related to parvus , but he mentioned only that these two species share a long and uniformly black head. He did not refer to body sculpture. Amongst our samples we have specimens of parvus with head and thoracic reticles lacking wrinkles ( Figs 24 , 27 ). Therefore, the key provided by Mirab-balou et al. (2017) seems incorrect in indicating the presence in parvus of pronotal reticles with wrinkles. An intermediate condition, with only the reticles on the posterior half of the pronotum having internal wrinkles, occurs in communis , phragmitesi sp.n. ( Fig. 22 ), ponkikiri , and unitatis . Mirab-balou et al. (2017) suggested that the head and pronotum of unitatis lack wrinkles in the reticles, but this is contrary to the descriptions in Wang (1993), Feng et al. (2007) and the website of Taiwan Encyclopedia of Life (http://taieol.tw/pages/109391). It seems that unitatis has wrinkles not only on the pronotum posterior half, but also on the mesoscutum and metanotal triangle. A further problem is that Feng et al. (2007) provided line drawings of shennongjiaensis without wrinkles in the thoracic reticles, but with more specimens now available the mesoscutum reticles of this species always have internal wrinkles medially ( Fig. 25 ).

Antennal segment IV sense cone. The forked sense cone on this segment is reported to vary in length between species. It is short in phragmitesi sp. n. described below, not extending to the mid-point of segment V ( Fig. 10 ). In contrast, more than 80% of species in this genus have this forked sense cone generally extending to the apex of V or mid-point of VI ( Figs 11–15 ). Unusually, brunneipennis has this sense cone extremely long and extending to the middle of VIII ( Fig. 19 ). This condition distinguishes brunneipennis from shennongjiaensis ; this latter species has the sense cone on IV extending only to the mid-point of VI ( Fig. 18 ). Wilson (1975) stated of brunneipennis in his key to Helionothrips species “sense cone on antennal segment IV reaching apex of segment VI”, but in the main text describing this species he states “sense cone on segment IV reaching the middle of VIII”. This suggests that in brunneipennis there may be variation in the length of the sense cone on antennal IV, or that there may have been a failure to note that the inner arm of this sense cone can be shorter than its outer arm. Examination of many specimens of shennongjiaensis indicate that this character is not stable, and relationships between these two species require further study. Similarly, mube has been distinguished from aino because the sense cone on IV surpasses the apex of VI ( Kudô, 1992) ( Fig. 17 ), whereas in aino it extends only to the middle of VI ( Wilson, 1975) ( Fig. 16 ). This sense cone is more variable than these two authors considered, and mube has recently been placed as a synonym of aino (Wang et al. [in press]).

Sternal pore plates of males. The number of pore plates varies between Helionothrips species. Among the 15 species recorded from China, males are unknown for ponkikiri and phragmitesi sp. n. Pore plates are absent in four species, annosus , cephalicus , lushanensis and unitatis . Circular pore plates are present in the other species: on sternite VIII only in linderae ; on sternites VII–VIII in brunneipennis , communis , errans , parvus , rugatus and shennongjiaensis ; on sternites VI–VIII in pallidus sp. n.; and on V, VI or VII–VIII in aino (Wang et al. [in press]). Kudô (1992) stated that the only distinct difference between aino and mube was in the number of male pore plates - in aino on sternites VII–VIII ( Fig. 30 ), but in mube on VI–VIII ( Fig. 28 ). However, Kudô (1992) also mentioned that pore plates of mube on VI might be vestigial. Of the 33 male specimens we previously identified as aino or mube 26 specimens have pore plates on VII–VIII, and 7 specimens on VI–VIII, including one with the pore plate on VI reduced to a very small dot ( Fig. 29 ). This variation indicates that the number of male sternal pore plates may not be entirely reliable to discriminate Helionothrips species.

Key to Helionothrips species from China

(* From original description)

1. Abdominal tergite VIII posterior margin with a complete comb................................................. 2

-. Abdominal tergite VIII posterior margin with comb interrupted medially......................................... 4

2. Antecostal line on abdominal tergites III–VIII forming three contiguous scallops; [metascutal triangle with posterior margin extending over metascutellum; male without pore plate on abdominal sternites]............................... annosus

-. Antecostal line on abdominal tergites III–VIII connected by a fine line, not forming contiguous scallops ( Fig. 41 )......... 3

3. Head yellow anterior to fore ocellus; antennal segments II and VI brown; male with pore plates on abdominal sternites VII and VIII........................................................................................... errans *

-. Head entirely dark brown; antennal segments II and VI yellowish brown; male lacking pore plate on abdominal sternites.............................................................................................. lushanensis *

4. Antennal segments I and II yellow ( Figs 11, 16–17 ).......................................................... 5

-. Antennal segments I and II yellowish brown to dark brown, never yellow......................................... 6

5. Head yellow anterior to fore ocellus and between antennal bases; mesoscutum with weak wrinkles in median reticles; male with pore plate only on abdominal sternite VIII........................................................... linderae *

-. Head completely dark brown; mesoscutum without wrinkles in reticles; male with pore plates on abdominal sternites VI/VII– VIII.............................................................................................. aino

6. Pronotum without wrinkles in most reticles, at most with weak wrinkles in only a few reticles ( Figs 23–24 ); male with pore plates on abdominal sternites VII–VIII.................................................................... 7

-. Pronotum with internal wrinkles in reticles, at least on posterior half ( Figs 20–22 ).................................. 9

7. Head yellowish brown, paler than pronotum; fore wing brown except for a small sub-basal pale brown patch............ 8

-. Head as dark brown as pronotum; fore wing with a sub-basal white band and apical half pale, apex brown ( Fig. 9 ).... parvus

8. Antennal sense cone on segment IV not beyond apex of VI ( Fig. 18 )................................ shennongjiaensis

-. Antennal sense cone on segment IV extend to mid of VIII ( Fig. 19 ).................................... brunneipennis

9. Pronotum with wrinkles only in reticles on posterior half ( Fig. 22 )............................................. 10

-. Pronotum with numerous wrinkles in all reticles ( Figs 20–21 ); head, meso- and metascutum also with internal wrinkles ( Figs 26 , 33, 35 ).......................................................................................... 13

10. Head, meso- and metascutum without wrinkles in reticles [antennal segments I, II and VI brown; forked sense cone on antennal segment IV at least extending to apex of V; male unknown]............................................. ponkikiri *

-. Head and mesoscutum with wrinkles in reticles, metascutal triangle with or without wrinkles in reticles................ 11

11. Metascutal triangle without wrinkles in reticles ( Fig. 40 ); antennal segments I–II darker than VI ( Fig. 10 ); antennal sense cone on IV short, not surpassing mid of V [male unknown]........................................... phragmitesi sp. n.

-. Metascutal triangle with wrinkles in reticles; antennal segments I–II as brown as or paler than VI; antennal sense cone on IV extending to VI...................................................................................... 12

12. Antennal segments I–II yellowish brown, VI dark brown; forked sense cone on segment IV extending to basal half of VI; male with pore plate on abdominal sternites VII–VIII..................................................... communis *

-. Antennal segments I–II as brown as VI; forked sense cone on segment IV extending to mid-point of VI; male without pore plate on abdominal sternites........................................................................... unitatis *

13. Antennal segment VI uniformly dark brown, VI as brown as II ( Fig. 13 ); female abdominal segment IX about 1.7 times as long as segment X............................................................................... pallidus sp. n.

-. Antennal segment VI light brown with basal half paler, VI paler than II; female abdominal segment IX at least 2.0 times as long as segment X........................................................................................ 14

14. Antennal segment I yellowish brown, paler than II ( Fig. 12 ); fore wing with a well-defined sub-apical pale band shorter than the middle brown area ( Fig. 7 ); male with pore plates on abdominal sternites VII–VIII......................... rugatus

-. Antennal segment I as brown as II ( Fig. 15 ); fore wing with a sub-basal white band, dark brown at fork and fading sub-apically ( Fig. 6 ); male without pore plate on abdominal sternites................................................ cephalicus

Figures

FIGURES 1–9. Fore wing of Helionothrips species, female. (1) H. shennongjiaensis; (2) H. brunneipennis; (3) H. annosus; (4) H. aino; (5) H. phragmitesi sp. n.; (6) H. cephalicus; (7) H. rugatus; (8) H. pallidus sp. n.; (9) H. parvus.

FIGURES 20–24. Pronotum of Helionothrips species, female. (20) H. pallidus sp. n.; (21) H. cephalicus; (22) H. phragmitesi sp. n.; (23) H. shennongjiaensis; (24) H. parvus.

FIGURES 25–30. Helionothrips species. Meso- and metanotum, female (25–27): (25) H. shennongjiaensis; (26) H. rugatus; (27) H. parvus. Male sternal pore plates of segments VI-VIII of Helionothrips aino (28-30): (28) Large pore plates on VI–VIII; (29) Vestigial pore plate on VI; (30) Pore plate absent on VI.

FIGURES 10–19.Antennae of Helionothrips species, female. (10) H. phragmitesi sp. n.; (11) H. annosus; (12) H. rugatus; (13) H. pallidus sp. n.; (14) H. parvus; (15) H. cephalicus; (16) H. aino (segment IV sense cone extends only to the middle of VI); (17) H. aino (segment IV sense cone surpasses the apex of VII); (18) H. shennongjiaensis; (19) H. brunneipennis.

FIGURES 31–42. Helionothrips species. H. pallidus sp. n. (31–37): (31) Female; (32) Male; (33) Meso- and metanotum, female; (34) Abdominal sternites V–VIII, male; (35) Head, female; (36) Abdominal tergites IX–X, male; (37) Abdominal tergites VIII–X, female. H. phragmitesi sp. n. (38–42): (38) Female; (39) Head, female; (40) Meso- and metanota, female; (41) Abdominal tergites I–III, female; (42) Abdominal tergites VIII–X, female.