Bactrothrips Karny, 1912

Okajima, Shûji & Masumoto, Masami, 2025, Two idolothripine genera, Bactrothrips and Megalothrips (Thysanoptera, Phlaeothripidae), from Asia between India and Taiwan, with descriptions of two new species, Zootaxa 5696 (4), pp. 491-516 : 493-496

Bactrothrips Karny

Bactrothrips Karny, 1912: 131 . Type-species: Bactrothrips longiventris Karny , by monotypy.

The genus Bactrothrips Karny was originally erected for B. longiventris as the type-species from Rio Muni, Spanish Guinea (= Republic Equatorial Guinea), and is closely related to both Idolothrips Haliday and Meiothrips Priesner ( Mound & Palmer 1983). It currently contains 53 species and is distributed mainly in the warmer parts of the Old World. The largest number of species has been described from Africa, with 11 from Asia, six from Australia, and one each from Europe, New Guinea and North America (ThripsWiki 2023). Of the 11 species distributed in Asia, seven have been described from Japan, two from China, and one each from Malaysia and India. However, many species described in the first half of the 20th century, especially from Africa, are confusing taxonomically and need to be reexamined. Most of them have been described based on a single specimen without a sufficient understanding of the characteristics of this genus. All six species distributed in Australia are quite different from the species known from Africa and Asia ( Mound & Tree 2011). For instance, four species, aliceae , houstoni , nativus and purplexus , have the prothoracic epimeral sutures complete or almost complete, and three species, aliceae , kranzae and perplexus, have rather long maxillary stylets. These species do not fit into some of the characteristics of the genus Bactrothrips that have been defined so far. That is, it raises the issue of not being able to apply the previous genus-level classification. This may be the result of their unique evolution after a long period of isolation, but it cannot be ruled out that they may comprise different genera. In particular, four species, excepting B. aliceae and B. nativus , are known only from a few or even a single specimen. Therefore, future continued investigations are needed to determine their exact taxonomic status.

There are several characteristics of this genus that we must understand, but of particular taxonomic importance is the intraspecific variation. There are sexual dimorphism and size related variation, as well as geographic variation. The presence of such intraspecific variations make the classification of this genus very difficult. Moreover, sometimes two or more species coexist on the same dead leafy branches. For instance, in the evergreen forest zone of Honshu, Japan, sometimes three or more species, five species maximum, can be observed from the same dead leafy branches. These difficult tasks can probably only be solved by closely examining a sufficient number of specimens from various regions. Research using molecules may be necessary, but it is unclear whether a clear conclusion can be reached by this alone. Under these circumstances, Haga (1975) and Haga and Okajima (1989) have suggested that the structural pattern of the Bournier’s Apparatus present in the female reproductive organ of Bactrothrips shows species-specificity and can be applied to species classification, at least in seven species from Japan. Subsequently, Okajima (2006) illustrated this apparatus in all seven Bactrothrips species from Japan (Figs 3–9) and showed that those had distinct species-specificity. This organ is a structure found near the aperture of the spermathecal duct into the vagina and was probably first described by Alexandre Bournier (1962). This structure was described in morphological detail based on four Bactrothrips species from Japan by Ueda and Haga (1987). In that study, however, the image identified as the Bournier’s Apparatus of B. honoris (see Fig. 2B in Ueda & Haga) was incorrect—it was actually that of B. pictipes . Conversely, the image identified as the Bournier’s Apparatus of unidentified ‘ Bactrothrips sp. J’ (see Fig. 2C in Ueda & Haga) was that of the true B. honoris . This mistake occurred because Bactrothrips species from Japan were not accurately classified at that time. As can be seen from this, B. honoris and B. pictipes are very similar in general appearance, but they can easily be accurately distinguished by comparing the female Bournier’s Apparatus. This organ is located beneath abdominal tergite IX (sometimes tergite VIII) and sometimes can be observed in well-depigmented specimens, but can be reliably as well as clearly observed by dissection (Figs 55 & 78 are images obtained by dissection, other images, e.g. Figs 66 & 88 , were observed in well-depigmented specimens). It consists of a tufted area and hilt (cf. Figs 55 & 78), and can be found by tracing the spermathecal duct.

On the other hand, Haga and Okajima (1989) also suggested that the shape of the male subgenital plate (this is probably homologous with the semilunar plate) is somewhat useful for identification of Bactrothrips species from Japan (cf. Figs 10–12). For example, the subgenital plate of B. brevitubus is elongate and tie-shaped (Fig. 10), thus easily distinguished from those of other species, and that of B. montanus is very wide (Fig. 12), and readily distinguishable from those of other species. Thus, in these two structures, the female Bournier’s Apparatus and the male subgenital plate, can be used to more easily and accurately classify Bactrothrips species. This study also found that this is at least useful for classifying all Bactrothrips species distributed in the Oriental region, but it is currently unclear whether this character state can be applied to African and Australian species. However, there is a major drawback that these structures can only be observed in reasonably prepared specimens in good condition, and not in unmacerated specimens. Therefore, it would be extremely difficult to observe with many older specimens including old type specimens.

Dang and Qiao (2012) recorded seven Bactrothrips species from China based on morphological and molecular data, including two new species. However, there are some problems with the content of that study. Especially, they classify these insect species by comparing relatively variable and unstable characteristics, such as the length of the prominent cephalic setae and the color of tibiae. In addition, the number of examined specimens is not sufficient for understanding the size relation and geographic variations. For instance, the length of four pairs of cephalic prominent setae is usually somewhat variable, and it sometimes differs greatly between the left and right side in the same individual. Moreover, despite the suggestion by Haga and Okajima (1989) and Okajima (2006), they did not examine female Bournier’s Apparatus and the male subgenital plate at all. Therefore, the two species newly described, B. elongatus and B. furvescrus , are not well defined and their actual taxonomic status is not clear. In particular, in this paper, it became clear that B. elongatus is a synonym of B. honoris (see below under B. honoris ). However, the status of B. furvescrus still cannot be confirmed because there is only a little information in the original description, but it seems to be somewhat similar to B. luteus . The setae on the surface of the tube are shorter in males than in females in furvescrus (see Figs 23 & 24 in Dang et al., 2012), but these characteristics are very similar to luteus . In addition, they divided B. brevitubus and B. quadrituberculatus based on the difference in the length of postocellar setae in their key (key couplet 6), but there are many individuals that cannot be accurately divided by this key due to intraspecific variation. If they had observed the female Bournier’s Apparatus and the male subgenital plate of these two species, they would have been able to distinguish them easily and more accurately. Moreover, they determined Fig. 38 in their study as the male abdominal segments VI–VIII of brevitubus , but the lateral tubercles on the tergite VI are rather thick and curved outwards. Those are very similar to the tubercles of quadrituberculatus , unlike those of brevitubus . On the contrary, in the same study, they determined Fig. 41 as quadrituberculatus , but the tubercles on the tergite VI are slender and curved inwards, and very similar to those of large males of brevitubus . However, it is unclear whether this is an error in the identification of the species or simply due to misplaced images.

In this article, 10 species are recognized from Asia excluding Japan.

Key to Bactrothrips species from Asia between India and Taiwan

[Excluding B. furvescrus Dang & Qiao. *: B. serraticornis is based on specimens from Java, Indonesia.]

1. Compound eyes prolonged posteriorly on ventral surface............................................. flectoventris

-. Compound eyes not prolonged posteriorly on ventral surface................................................... 2

2. Reticles on pelta with different patterns in anterior and posterior portions ( Figs 22–25 ); female Bournier’s Apparatus small, tufted area vestigial (Figs 6, 42 & 43); antennal segment III relatively short ( Figs 17–21 ), about half the length of head; male tubercles on tergite VI curved outwards ( Fig. 26 ) at least in large individuals; abdominal tergite VII without distinct tubercles even in large male ( Fig. 26 )........................................................................ honoris

-. Reticles on pelta with a similar pattern in anterior and posterior portions (cf. Figs 62 & 63 ); female Bournier’s Apparatus large, tufted area well-developed (cf. Figs 55 & 78); antennal segment III relatively long (cf. Figs 45 & 70), usually longer than 0.55 times as long as head; male tubercles on tergite VI variable in shape; abdominal tergite VII with distinct tubercles at least in medium to large male (cf. Figs 61 & 75 ), but without tubercles in pictipes ........................................ 3

3. Abdominal tergites II–VII (or VIII) each with a pair of lateral ‘faded windows’ (cf. Fig. 39 ); male tubercles on tergite VI largely yellowish with dark base, almost straight, inner margin almost smooth (cf. Fig. 61 )................................. 4

-. Abdominal tergites without lateral ‘faded windows’; male tubercles on tergite VI largely brown, not straight, curved inwards (cf. Figs 48 & 75) or outwards at least medium to large individuals.............................................. 5

4. Antennal segment III usually longer than 0.6 times as long as head, 0.58–0.65 times in female, 0.63–0.67 times in male; head 2.02–2.22 times as long as wide in both sexes; setae on tube short and sparsely scattered in male ( Fig. 65 ), usually shorter than 50µm, but longer in female ( Fig. 64 ); female Bournier’ Apparatus with stout hilt ( Fig. 66 )........................ luteus

-. Antennal segment III shorter than 0.6 times as long as head, 0.54–0.57 times in female, 0.56–0.59 times in male; head 2.26– 2.34 times as long as wide in female, 2.31–2.40 times in male; setae on tube long and closely scattered in both sexes, usually longer than 70µm; female Bournier’s Apparatus with slender hilt (Fig. 8).................................... pictipes

5. Postocellar setae minute, usually almost as long as a diameter of posterior ocellus; male tubercles on tergite VI stout, distinctly curved outwards at least in medium to large sized individuals; male sub-genital plate tongue-shaped; female Bournier’s Apparatus well developed, irregularly funnel-shaped with stout hilt (Fig. 9)........................ quadrituberculatus

-. Postocellar setae elongate, usually much longer than a diameter of posterior ocellus; male tubercles on tergite VI rather slender, curved inwards at least in medium to large sized individuals; male sub-genital plate slender, tie-shaped (cf. Fig. 56) ( idolomorphus -group).................................................................................. 6

6. Postocellar setae elongate, longer than interocellar setae; tufted area of female Bournier’s Apparatus widely spread laterally (Fig. 55); mid and hind tibiae largely yellowish, with brown shading sub-basally (Figs 52 & 53)............. idolomorphus

-. Postocellar setae shorter than interocellar setae; tufted area of female Bournier’s Apparatus triangular (cf. Figs 88 & 89 ); mid and hind tibiae distinctly bicolored (cf. Figs 83 & 84 )......................................................... 7

7. Prothoracic epimeral accessory setae rather elongate, usually 0.3–0.6 times as long as epimeral setae; tufted area of female Bournier’s Apparatus almost equilateral triangular (Figs 3 & 89), or wider................................ brevitubus

-. Prothoracic epimeral accessory setae short, shorter than 0.3 times as long as epimeral setae; tufted area of female Bournier’s Apparatus almost triangular, but slender (cf. Fig. 88 )......................................................... 8

8. Mid tibiae largely yellowish, usually dark brown at basal half ( Fig. 83 ); club-head of antennal segment III brown to dark brown, distinctly darker than pedicel ( Fig. 81 ); postocular setae pair II elongate, usually longer than three-quarters the width of head; antennal segment III elongate, 0.63–0.71 (means±SD=0.66±0.03, n=16) times as long as head in female, 0.67–0.75 (means±SD=0.72±0.03, n=14) in male.......................................................... serraticornis *

-. Mid tibiae largely dark brown, with apical one-quarter yellow ( Fig. 72 ); club-head of antennal segment III scarcely shaded with brown, not darker than pedicel ( Fig. 70 ); postocular setae pair II shorter, usually shorter than half the width of head; antennal segment III somewhat shorter, 0.56–0.63 (means±SD=0.60±0.02, n=22) times as long as head in female, 0.52–0.64 (means±SD=0.60±0.03, n=19) in male..................................................... malayanus sp. nov.

Figures

FIGURES 1–2. Bactrothrips species: (1) B. honoris, male; (2) B. pictipes, female.

FIGURES 57–67. Bactrothrips luteus from Thailand: (57) head, female; (58) head, male; (59) antennal segments III & IV, female; (60) antennal segments V–VIII, female; (61) abdominal segments VI & VII, male; (62) pelta, female; (63) pelta, male; (64) setae on tube, female; (65) setae on tube, male; (66) Bournier’s Apparatus, female (a: tufted area, b: hilt); (67) subgenital plate, male.

FIGURES 79–89. Bactrothrips serraticornis from Java, Indonesia 79–88: (79) head, female; (80) head, male; (81) antennal segments III & IV, female; (82) antennal segments V–VIII, female; (83) mid tibia, femle; (84) hind tibia, female; (85) pelta, female; (86) pelta, male; (87) abdominal tubercles, male; (88) Bournier’s Apparatus, female. B. brevitubus, female: (89) Bournier’s Apparatus.

FIGURES 13–26. Bactrothrips honoris. Head 13–16: (13) female from Taiwan; (14) male from Taiwan; (15) female from Java; (16) male from Java. Antennal segments III–VIII, female 17–21: (17) Taiwan; (18) Java; (19) Peninsular Malaysia; (20) Mindanao Is., the Philippines; (21) S. Sulawesi. Pelta 22–25: (22) female from Taiwan; (23) female from Java; (24) male from Java; (25) male from Peninsular Malaysia. (26) Abdominal tubercle, male from Java.

FIGURES 27–43. Bactrothrips honoris. Hind tibia, female 27–33: (27–29) Taiwan; (30) Java; (31) Peninsular Malaysia; (32) Mindanao Is., the Philippines; (33) S. Sulawesi. Mid tibia, female 34–38: (34) Taiwan; (35) Java; (36) Peninsular Malaysia; (37) Mindanao Is., the Philippines; (38) S. Sulawesi. (39) Abdominal segments VI and VII, female (arrows indicate ‘faded windows’), female from Java. Male subgenital plate 40–41: (40) Taiwan; (41) Java. Female Bournier’s Apparatus 42–43: (42) Java; (43) Peninsular Malaysia.

FIGURES 68–78. Bactrothrips malayanus sp. nov.: (68) head, female; (69) head, male; (70) antennal segments III & IV, female; (71) antennal segments V–VIII, female; (72) mid tibia, femle; (73) hind tibia, female; (74) pelta, female; (75) abdominal segments VI–VIII, male; (76 & 77) subgenital plate, male; (78) Bournier’s Apparatus, female (a: tufted area, b: hilt).