Perochaeta orientalis (de Meijere, 1913)

Ang, Yuchen, Wong, Ling Jing & Meier, Rudolf, 2013, Using seemingly unnecessary illustrations to improve the diagnostic usefulness of descriptions in taxonomy-a case study on Perochaeta orientalis (Diptera, Sepsidae), ZooKeys 355, pp. 9-27 : 11-18

Perochaeta orientalis (de Meijere, 1913) Figs 1-6

Material examined.

Holotype ♂ (Figs 4A, B). Type locality: "Chip Chip" (Jiji, = 集集) Township, Nantou County (南投), Taiwan ROC [likely, approximate coordinates 23°50'7"N, 120°46'4"E] (type label info: "Formosa Sauter. Chip-Chip 909. III. Nemopoda orientalis det de Meijere. Type."). ♂ in the Hungarian Natural History Museum, Budapest, Hungary.

Additional material

(Figs 1-3). Locality: Brinchang Jungle Trail, Cameron Highlands, Pahang, Peninsular Malaysia [4°30'9.55"N, 101°23'20.85"E. 1600m ASL]. Isoline culture based on ♀ collected 4.I.2011 (R. Meier). ♂♂♀♀ in the Raffles Museum of Biodiversity Research.

Morphological diagnosis (adult).

Male Perochaeta orientalis are most easily differentiated from other described Perochaeta species based on two large, flattened bristles of the main tuft on the sternite appendage, of which one has a triangular, submedial protrusion (red arrows on Fig. 1F) while all other described Perochaeta species have unmodified bristles (Figs 5 with suffix ‘A’). The surstylus in Perochaeta orientalis (Fig. 1G) is also unique in that the median inward protrusion consists of a large, broad-based triangle that spans a third of the surstylus (see Figs 5 with suffixes ‘B’ and ‘C’). The hind tibia of Perochaeta orientalis also has a distinct, raised osmeterium (Fig. 1C) which is barely visible or missing in other Perochaeta . Adult female Perochaeta orientalis can be distinguished from the females of Perochaeta dikowi (the only other species with a female description) based on the presence of sternites 3 and 4 (Fig. 2B), which are missing in the latter. For both sexes, the pleural, thoracical microtrichosity for Perochaeta orientalis (red arrow on Fig. 1B) is most similar to that of Perochaeta exilis (Fig. 5ED) because it is tomentose on the posterior third of the anepimeron and the dorsal tip of the greater ampulla. In contrast, Perochaeta cuirassa and Perochaeta lobo (Fig. 5CD) have a glossy greater ampulla, while Perochaeta dikowi is pruinose wholly on the greater ampulla and on slightly less than the posterior half of the anepimeron (Fig. 5DD).

Morphological description.

Colour. Similar in males (Fig. 1A) and females (Fig. 2A). Head capsule black except for face and a connecting thin strip below the eye, which is light-brown. Antennal pedicel dark brown, first flagellomere paler. Proboscis dark-brown with yellow labellum. Thorax wholly black, abdomen with glossy dark-brown tergites and sternites. All femora largely yellow with diffuse obfuscate rings post medially (faint on fore femur). Fore tibia wholly yellow; mid tibia darkened on the basal half; rear tibia entirely dark. All tarsi with first two segments yellow and last three dark-brown. Wing cells clear except for darkened basicostal cell and basal third of costal cell. Veins mostly dark brown. Calypter creamy; haltere whitish with brown base.

Head. Similar in males and females (Figs 1A, 2A). Roundish; facial carina short and shallow, facial area receding. Gena and parafacial region narrow. Ocellar prominence and occipital region lightly microtomentose. Chaetotaxy: ocellar longer than divergent postocellar; 1 outer vertical; inner vertical absent; orbital very reduced; 2 vibrissae; 2-3 weak postoculars; Lower fascial margin lined with setulae.

Thorax. Similar in males and females. Scutum, scutellum and subscutellum lightly microtomentose. Mediotergite microtomentose but glossy in the medial region (Figs 3ME, 3FE). Scutellum twice as wide as long (Figs 3MA, 3FA). Pleural pruinosity pattern (Fig. 1B): Protonotopleural lobe glossy on pleural region but microtomentose on dorsal region. Proepisternum fully microtomentose. Anepisternum largely glossy with anterioventral region densely microtomentose. Katepisternum with dense tomentosity except for glossy anterioventral region. Greater ampulla lightly microtomentose on the dorsal tip. Anepimeron glossy with lightly microtomentose strip on posterioventral region. Katatergite, katepimeron, metakatepisterum, meron and metepimeron lightly-dusted. Chaetotaxy: 1 apical scutellar, 1 reduced, setulae-like basal scutellar, 1 dorsocentral, 1 postalar, 1 supraalar, 2 notopleural, 1 postpronotal, 1 anepisternal and 1 posterior spiracular. Postpronotoum, prescutum and anepisternum with few, sporadic setulae.

Legs. Fore legs unmodified in males and females; all femora and tibiae without robust setae except for a longitudinal row of short spines on the anterior basal half of mid femur. Male rear tibia with a small but distinct osmeterium with raised hairs at the posteriodorsal region, and with three enlarged ventral setae on basitarsus (Fig. 1C). Females similar but lacking in osmeterium.

Wings. Similar in males and females. Slender. Without apical pterostigma. Veins bare. Wing microtrichia pattern (basal half; Fig. 1D): cells covered with microtrichiae except for subcostal, basal-medial, posterior-cubital cells and alula. Costal, radial 1, radial 2+3, radial 4+5, basal-radial, disco-medial, anterior cubital cells and anal lobe with portions lacking microtrichia. Radial-medial cross-vein divides discal-medial cell by ratio of 2: 1. Length: 4.4-4.8 mm.

Male abdomen. Ventral view (Figs 1E, F). Syntergite 1+2 to tergite 5 normal, tergite 6 missing, syntergite 7+8 present and extending ventrad as a narrow sclerite. Spiracles 1-4 on intersegmental membrane, spiracle 5 on ventral margin of tergite 5, spiracle 7 and 8 adjacent on margin of syntergite 7+8. Sternite 1 as a thin lateral band with tapering ends while sternite 2 is triangular, tapering posteriorly; sternite 3 is longitudinally oblong. Sternite 4 heavily modified into paired moveable appendages [Fig. 1F; see Bowsher et al. (2013) for a discussion on the evolution of the appendages and Fig. 5 for sternite appendage illustrations of other Perochaeta ]: largely desclerotized except for anterior margin as well as two rectangular regions laterally off the median. Two stout moveable appendages branch off laterally, each with a tuft of small short bristles facing the inner side of the sternite and two large, flattened and inward-curving bristles on the apices, of which one is pinched sub medially, resulting in a tooth like furcation on the inward side (red arrows on Fig. 1F).

Hypopygium (Fig. 1G). Cercal plate with two very weak lobes, each with one setae. Hypopygium triangular with a large tooth-like projection originating from the inner base of the surstylus. Surstylus itself fused to hypopygium and branches off dorsally. Each surstylus is curved ventrally, with a large, flattened, inward-facing posteriomedial triangular process; terminus with “teeth” and setulae.

Phallus (Fig. 1H). Basal region with scales on left side and relatively smooth on right side (crinkles and cracks on the surface are artifacts due to drying process). Basal region with large flap adorned with numerous long spines. Distal portion short (ca. 1/3 of basal portion) and membranous. We refrain from assigning terminology, for reasons explained in Discussion.

Female abdomen (Fig. 2 B–E). Syntergite 1+2-tergite 5 similar to male, tergites 6 and 7 well defined and sclerotized. Spiracles 1-5 in intersegmental membrane while spiracles 6 and 7 are within the tergites. Sternites 1 and 2 similar to male, sternite 3 as a very thin longitudinal strip. Sternite 4 also a thin strip with barely visible sclerotization and a diffuse margin, sternite 5 missing. Sternites 6 as a lateral rectangle and sternite 7 tapering posteriorly. Postabdominal segments 6 and 7 with the tergites and sternites separated laterally, the sternites (like the tergites) thus very broad and short; segment 8, when not invaginated, long, extended posteriorly and ventrally, with a ventral element (sternite 8) on each side that remains separated at tip and a dorsal element (tergite 8) that forms the usual pair of ring-like bars that do not quite touch apically. Cercus small and round, with hypoproct present, bare.

Mating behaviour.

Here, we conducted 36 mating trials with virgin males and females. Only two of these trials were successful (=5.6% mating success rate), and the copulation time for these two were ca. 75 and 72 minutes. Virgin mating behaviour can be divided into four phases: (1) courtship, (2) approach and mount, (3) copulation and (4) separation. The copulatory profile (section 3) for Perochaeta orientalis is shown in Fig. 6, based on a frame-by-frame analysis of one of the trials and documented in Video 1 (time in video given as mm:ss). Where available, we will compare and differentiate the behaviour of Perochaeta orientalis with Perochaeta dikowi ( Ang et al. 2008b) which is the only other Perochaeta species with a known mating profile. Our efforts to provide detailed mating behaviour for Perochaeta orientalis is part of a larger series of papers investigating of mating behaviour in sepsids (e.g., Ang et al. 2008b, Puniamoorthy et al. 2008, Puniamoorthy et al. 2009, Tan et al. 2010, Tan et al. 2011). As discussed in Puniamoorthy et al. (2009), attention to detail is important because sepsid mating behaviour is apparently species-specific.

Courtship. When the male detects and shows interest in a female, he courts the female by using a "wing flutter dance"; i.e., he rapidly circles the female from his side while fluttering the wing facing the female (00:07). This behaviour is not observed in Perochaeta dikowi .

Approach and mount. The male will approach the female from the rear and attempt to mount her. Unlike most sepsid species, Perochaeta orientalis males lack modified fore legs, and do not clasp the female wing or perform pre-copulatory behaviours when mounted like other sepsids ( Puniamoorthy et al. 2008). Instead, he mounts similarly to Perochaeta dikowi ; using his fore tarsi to hold on to the female’s abdomen whilst bending his abdomen forward. He then extends his sternite brush to contact the genital region, while the surstylus attempts to clasp the female genitalia (00:15 & 00:29). A crucial difference between the two species is that Perochaeta dikowi uses his sternite brush to contact the anterior portion of the female abdomen before sliding towards her posterior, while Perochaeta orientalis immediately contacts the genital region (see attempt in 00:15). At this stage, females show strong rejection behaviour towards the males which explains the low mating success rate. Males are kicked with mid- and hindlegs and/or the abdomen is raised to prevent genital contact (00:15). All resisting females remained unmated and only those males succeeded in mating that encountered willing females (00:29). In Perochaeta dikowi , female resistance is much lower and mating success rates were 28.6%.

Copulation (Fig. 6). Once the male locks its genitalia with the female, they copulate for a long time (73.7 ± 1.2 min; based on the two successful trials), which is over 3 times longer than that in Perochaeta dikowi (22.6 ± 2.48 min). There are periods of rest and activity during copulation. During rest, males place their fore tarsi on the female pronotal callus while mid- and rear legs are splayed out. During active periods, the male displays five types of behaviours: "M1: fore leg head tap ”– males using fore tarsi to tap repeatedly on female head (00:41), "M2: rear leg rub ”– males rubbing rear legs together (01:03), "M3: rear-mid-leg rub ”– males rubbing rear legs with mid legs (01:10), "M4: mid legs wing tap ”– males using mid legs to tap repeatedly on female wing (01:18) and "M5: mid legs abdomen tap ”– males use mid legs to tap repeatedly on female abdomen (01:29). Behaviours M3 and M4 mostly occur after M1 and M2, suggesting a transfer of substance from the rear tibial osmoteria to the mid legs and then onto the female wing and/or abdomen. Female resistance was recorded even after copulation commenced; the female mostly used her mid legs (F1; 01:39) and only occasionally her hindlegs to push against the male (F2; 01:51). The female also indulged in grooming herself at times, either performing a rear leg rub (F3; 02:00) or a fore leg-head rub (F4; 02:06)

Separation. Just prior to separation, the male performs the "fore leg head tap" as well as the consecutive "rear-mid-leg rub" and "mid legs abdomen tap". The separation event itself is initiated by the male, where he turns 180° and pulls away from the female (02:15). Both males and females will also use their rear legs to push against each other during this time. This is similar in Perochaeta dikowi .

Distribution, laboratory records and DNA sequence information.

Biogeography. Perochaeta has been consistently found only in mid- to high-elevation areas [see Ang and Meier (2010) for a discussion on the genus’s biogeographical distribution]. Perochaeta orientalis itself was first collected by Sauter from two township localities in the central highlands (Nantou County; = 南投縣) of Taiwan: Jiji ("Chip Chip", = 集集) and Puli ( “Polisha”, = 埔里; approximate coordinates 23°57 ’56” N, 120°57 ’57” E) ( de Meijere 1913). While the elevation of these two townships are relatively low (ca. 300m for Jiji and 500m for Puli), they are both immediately enclosed by mountain ranges that reach to excesses of 2500m. Specimen collection in Sauter’s expedition would likely be from these mountainous regions. It is thus possible that Perochaeta orientalis -like its other congeners in Perochaeta -is a higher-elevation specialist limited to the hills and mountains of the Oriental region. It has been recorded in Taiwan, Indonesia (Sulawesi I.), East and West Malaysia, as well as the Philippines (Luzon I., Mindanao I.) ( Ozerov 2005).

Laboratory records. Under laboratory conditions, Perochaeta orientalis has been bred successfully from bovine (cow and gaur) dung. They are also attracted to this substrate in the wild, which makes sampling an area for Perochaeta a “bait-and-wait” strategy.

DNA sequence information. Molecular data from our new Perochaeta orientalis material are presented as part of the updated sepsid phylogeny ( Lei et al. 2013). Nine mitochondrial and nuclear genes are sequenced and uploaded to Genbank. Their accession numbers are: 12S - KF199478, 16S - KF199525, COII - KF199667, COI - KF199842, CYTB - KF199714, 18S - KF199572, 28S - KF199618, ATS - KF199795, H3 - KF199739. Genetic distances for COI between existing species with DNA records ( Perochaeta cuirassa , Perochaeta dikowi and Perochaeta lobo ) were calculated using SpeciesIdentifier ( Meier et al. 2006). Perochaeta orientalis has the most similar sequence to Perochaeta dikowi (3.82%; Table 1), a distance that is well in excess of what is normally found between dipteran species ( Meier et al. 2008).