Genus Diploptera Saussure, 1864

Prosoplecta (Diploptera) Saussure, 1864a: 325; Saussure, 1864b: 177, fig. 28.

Type species Prosoplecta (Diploptera) silpha Saussure, 1864a .

Diploptera: Saussure, 1864b: 166, 177, elevated from subgenus; Walker, 1868: 57; Walker, 1869: 125; Brunner von Wattenwyl,1893: 40.

Eleutheroda Brunner von Wattenwyl, 1865: 264; Walker, 1869: 125, synonymized with Diploptera; Brunner von Wattenwyl 1893: 40, Walker’s revision was accepted.

Diagnosis. Diploptera is distinguished from other blaberid cockroaches mainly by its wings: tegmen heavily sclerotized, resembling the elytron of beetles; hindwing folds following the similar pattern of beetle’s, with abundant cross-veins and a transverse fold, along which the hindwing reflexes and which runs transversely and nearly halves the hindwing, even with an uncommon anal fold ending at the apical angle. Compared to other cockroaches with transversely reflexed hindwings, Diploptera possesses a different appendicular field on which cross-veins and several longitudinal veins are present, whilst other groups have one or two anal veins only, such as Anaplecta and Plectoptera . Diploptera is also unique by the three-segmented cercus, whilst that of other blaberid cockroaches is multi-segmented or coalesced to one segment.

Redescription. General. The insects resemble beetles. Body size medium to small, females always obviously larger than males. Head relatively large, exposed; ocular distance accounting for about half of head width, subequal to that between antennal sockets, greater than ocellar distance; ocellus spot oval or crescent, oblique; antennae always with the same length of body or longer. Pronotum and tegmina always setose or pubescent. Mesonotum with an exposed triangular bump bordered by pronotum and tegmina, which resembles a scutellum and was described as so (see Anisyutkin 2007) but is not that case. Tegmina and hind wings fully developed. Tegmina strongly sclerotized, with veins almost indistinguishable; the base in ventral view with a ridge along the subcosta (Sc); the covered portion of right tegmen translucent. Hindwings large (Figs. 31, 42 & 48), about two times the length of tegmina when unfolded, the costal border sclerotized (see grey coloration in Figs. 31, 42 & 48); venation reticular, longitudinal veins curved near the transverse fold (tfd), which runs across the middle of hindwing and results in a large appendicular field occupying nearly half of the hindwing; subcosta (Sc) and media (M) simple, radius (R) bifurcated near arculus (= mp-cua cross-vein); anterior cubitus (CuA) robust, branched at tfd; first three anal veins (AA, AP1 and AP2) curved strongly near tfd, AA towards costal margin (but the curved end may be a splice with a cross-vein), whilst the AP veins towards outer margin; anal fold (afd) running between AA and AP1, ending at the apical angle; branches of AP1 occupying a remarkably large area. Front femur type C1; tarsal pulvilli large, present on the first to the fourth proximal tarsomeres; claws symmetrical and unspecialized; arolia large. Cerci tapered, with three segments and the basal one accounting for more than half of the total length.

Male. Abdomen with T1–T9 specialization and tergal gland absent or invisible; T8 and T9 covered, S8 covered by S7. Supra-anal plate (T10) subtrapezoidal, specialized with a transverse membranous field (m.) in the middle; right paraproct with a hook at the apex. Subgenital plate (S9) asymmetrical (Figs. 33, 38, 44 & 50), with right posterolateral margin emarginate and with two dorsal sclerotized lobes (S9d), the left larger than the right; styli similar, fingerlike, of which the insertions on the subgenital plate are membranous, the left membranous area markedly smaller than the right. Genitalia with hook-like sclerite L3’ (= R 2 in McKittrick 1964, similarly hereinafter) on the right side, main sclerite of L2’ (= L2vm) rodlike, apical sclerite of L2’ (= L2d) discoid; R’ (= L1) composed of two sclerites, of which the folded one sandwiches part of the other, the latter with a long, arcuate, and spinous structure running parallelly with the anterior margin of the main part of the sclerite (Figs. 34, 39, 45 & 51). The spatial arrangement of genitalia is as indicated in Fig. 73.

Female. Abdomen with T8 covered by T7, T 9 in anterior-posterior extension extremely short and almost thready. Supra-anal plate (T10) subtrapezoidal, without membranous specialization. Subgenital plate (S7) with posterior margin rounded.

Distribution (Fig. 1). Oriental Region and the north of Australian Region, mostly Southeast Asia and South China.

Taxonomic notes. Since early descriptions of species were too simple and were based mainly on body size and color pattern, there would be difficulties in separating one species from each other. It is noteworthy enough that the relative length of tegmen had been used as a diagnostic character; however, as a result of the retractable abdomen, it is not adequate to rely on whether the tegmen exceeds the end of abdomen or not. The relative length of tegmen could be of diagnostic value by comparing it to the size of pronotum, which stands reliably for body size; however, tegmen length may be varied too among conspecific individuals so as to make itself less valuable in taxonomy.

After examining the types and other specimens, we suggest establishing a punctata -species-group containing the following nominal species: D. punctata, D. minor, D. erythrocephala Princis, 1950 and D. parva Princis, 1953 . These are almost indistinguishable from each other, and there is the probability that one or more may become junior synonyms with further research.

Details are given within the entries for taxa below.

Remarks. Diploptera is unique among genera of cockroaches in that the species vary more in the shape and markings of pronotum (Figs. 2–16) than in the male genitalia and genital segments. Such a significant differentiation in the posterolateral angles of pronotum could indicate two routes of evolution and the pronotum is almost uniformed among species in most of cockroach genera; when pronotal shape is various in one genus, it is often correlative to wings development and the cercus length, i.e., shorter wings and cerci may company with a pronotum with sharper posterolateral angles, but Diploptera is not that case. We could definitely divide the genus into two groups by the shape of pronotum (cp. Figs. 2–12 with Figs. 13–16); but aside from male genitalia and genital segments, other characters are also less distinct, such as tergal specialization, front femur type and venation, therefore the species should remain in one genus rather than be placed in two or more artificial genera based merely on such a single character.

Some cockroach genera also have a hindwing with a reflexed area (appendicular field or apical triangle), but they evolve probably in a different way from Diploptera . Reflexed area of them is bordered anteriorly by CuP and posteriorly by AP, the fact could tell that the area in evolutionary history is enlarged from the narrow space between CuP and AP apically, along which the folding lines run; the area is free of cross-veins as its original. Differently, Diploptera gained the appendicular field by cutting off the main veins at the middle and thus the apical half of these veins as well as the apical half of the hindwing can reflex over their basal half; the area bordered by CuP and AP is full of cross-veins resulting from the presence of abundant branches of AP for supporting this area.

Checklist of Diploptera species (9) and subspecies (2) worldwide

D. bicolor Hanitsch, 1925: 102 Borneo

Diploptera elliptica sp. n. South China

D. erythrocephala Princis, 1950: 163 Borneo

D. maculata Hanitsch, 1925: 104 Borneo

D. minor (Brunner von Wattenwyl, 1865: 295, Eleutheroda) Philippines

Diploptera naevus sp. n. China (southeast of Xizang)

D. nigrescens Shiraki, 1931: 174 South China

Diploptera nigrescens guani subsp. n. South China (mainland)

D. nigrescens nigrescens Shiraki, 1931: 174 South China (Taiwan Island)

D. parva Princis, 1953: 208 Java and Sumatra

D. punctata (Eschscholtz, 1822: 86, Blatta) South Pacific, Southeast Asia and South China

Key to Diploptera species and subspecies worldwide

1. Pronotum more or less suboval, without sharp posterolateral angles (Figs. 13–16)................................... 2

- Pronotum subsemicircular or subtrapezoidal, with sharp posterolateral angles (Figs. 2–12)............................ 4

2. Pronotum unicolor in brown (Figs. 15–16).............................................. Diploptera elliptica sp. n.

- Pronotum with markings in blackish and orange-yellowish (Figs. 13–14).......................................... 3

3. Pronotum with disc blackish and lateral borders orange-yellowish (Fig. 13)................................. D. bicolor

- Pronotum orange-yellowish, striped with a pair of vittae and a macula in blackish (Fig. 14).................. D. maculata

4. Pronotum with disc blackish and wide lateral borders orangish (Fig. 9)........................ Diploptera naevus sp. n.

- Pronotum unicolor (Figs. 2–8), or limbate narrowly (Figs. 10–12)............................................... 5

5. Pronotum blackish, limbate in reddish narrowly (Figs. 10–12)......................................( D. nigrescens)6

- Pronotum unicolor in brownish (Figs. 2–8)............................................ ( punctata -species-group) 7

6. Head blackish (Figs. 29–30, 56), locality Taiwan Island .................................... D. nigrescens nigrescens

- Head reddish brown (Figs. 27–28), locality south of mainland China ............... Diploptera nigrescens guani subsp. n.

7. Body relatively large, legs dark brown............................................................ D. punctata

- Body relatively small, legs (or except coxae) yellowish to reddish brown.......................................... 8

8. Tegmina with distinct punctations......................................................................... 9

- Tegmina with very indistinct punctations............................................................. D. parva

9. Head reddish brown..................................................................... D. erythrocephala

- Head black or blackish brown...................................................................... D. minor