A black-and-red stick insect from the Philippines – observations on the external anatomy and natural history of a new species of Orthomeria

Abstract A new stick insect of the genus Orthomeria Kirby, 1904 (Phasmatodea, Aschiphasmatidae) is described from the Philippines. Orthomeria (Orthomeria) kangi sp. n. is readily distinguished from all other congeners by the distinctive blood red colouration of the costal region of the hind wings. Major features of the external morphology of adults, eggs, and first-instar nymphs are illustrated. Locomotory attachment pads are of the smooth type with irregular microgrooves on the contact surface. An unusual condition of male terminalia is the absence of tergal thorn pads on segment 10. The male clasping organs are represented by an elongated vomer terminating in a prominent spine, and by incurved cerci featuring a bilobed apex equipped with a sharp blade-like ridge. Intraspecific variation in body colouration and hind wing length occurs in females. The new species lives at 400-650 m elevation in the surroundings of the Sablang and Tuba regions, in the Benguet Province of Luzon island. Host plants include Ficus spp. (Moraceae), and Pipturus spp. and Leucosyke spp. (Urticaceae). Observations on the mating and defensive behaviour are presented. Orthomeria (Orthomeria) catadromus (Westwood, 1859) is recognised as a junior synonym of Orthomeria (Orthomeria) pandora (Westwood, 1859), syn. n. A lectotype is designated for both species. Finally, an updated identification key to the species of the subgenus Orthomeria is provided.


Introduction
The stick insect genus Orthomeria Kirby, 1904 belongs to the South-east Asian family Aschiphasmatidae (Bragg 2001), and includes ten species divided into two subgenera (Bragg 2006). The nominal subgenus Orthomeria, characterised by a relatively thickened body with dark brown or black basic colouration, comprises seven species found in Borneo, Seram, Sulawesi, Sumatra, and the Philippines (Bragg 2001). The subgenus Parorthomeria, characterised by a slim green body and setose eggs, contains the remaining three species that are endemic to Borneo (Bragg 2006).
As part of our research on the Philippine stick and leaf insect fauna (Gottardo 2007;Gottardo 2008;Hennemann et al. 2009;Bresseel 2012), a field expedition was carried out to the Benguet province of Luzon island during which several specimens of Orthomeria were found. After a careful examination of the general anatomy, the specimens were assumed to represent a new species of the subgenus Orthomeria showing an original set of morphological traits, including a distinctive red colouration on the wings which was not previously reported within the genus (see Bragg 2001).
The aim of this study is to provide a formal description of the new species. Some features of the external anatomy such as attachment devices and male terminalia are characterised in detail for the first time in Orthomeria. The morphological data are integrated with observations on the habitat and various life traits. We also provide an updated identification key to the species of the subgenus Orthomeria adapted from Bragg (2001).

Material and methods
Orthomeria specimens were collected at night by searching the vegetation along road sides. Specimens were euthanized in glass jars with fumes of ethyl acetate, and subsequently preserved dried and pinned. Some adult females were kept alive to obtain eggs. Linear body dimensions were taken with digital calipers (to the nearest 0.1 mm). The description of chromatic characters was based on live specimens. Observations on the external morphology were carried out with a Zeiss Stemi DV4 stereo light microscope. Photomicrographs were taken with a Nikon D200 SLR digital camera equipped with Nikon Micro-Nikkor AI-s 105 mm f/2.8 lens or with Nikon 24 mm f/2.8 AI-s lens. For scanning electron microscopy (SEM) observations, samples were dehydrated through a graded ethanol series and dried with CO 2 at the critical point (Balzers CPD 030). Dried samples were mounted on aluminium stubs, sputter coated with gold (Balzers MED 010), and observed with a Philips XL20 scanning electron microscope operating at an accelerating voltage of 10 kV.
External eggshell morphology. Capsule light brown, oval in outline, laterally flattened, surface minutely pitted (length, 2.6-2.7 mm; height, 2.3 mm; width, 1.6-1.7 mm) (Fig. 10). Operculum mid brown, elongate-oval with a medial longitudinal furrow, slightly convex in lateral aspect (height, 1.8 mm; width 0.7 mm). Opercular angle negative. Micropylar plate visible in lateral aspect, structured as pale brown stripe surrounding the entire capsule and delimited by a thin yellow rim extending also along the opercular opening area. Micropylar cup close to the posterior pole.  Description of the first-instar nymph. Body length ca. 8.9 mm. Head, prothorax, and abdominal segments V-X black; meso-and metatorax, and abdominal segments I-IV brown (Fig. 11A-B). Scape and pedicel white; flagellomeres black with white distal dot. Palpomeres of labial and maxillary palps white. Hind margin of thoracic and abdominal terga white. Femora brown with a white spot in the middle. Tibiae black with a central white band. Tarsi with proximal tarsomere white, remainder black.
Geographic distribution. The new species is so far reported only from the Benguet province, Luzon island, Northern Philippines (Fig. 12). Specimens have been found in the Sablang region (Barangay Bayabas, Mt. Bilbil) and in the Tuba region (Mt. Calugong).
Natural history observations. The studied locality, Sablang, is a mountainous region (400-650 m elevation) of the Benguet Province, in the north-west Philippines. It is characterised by the presence of small communities scattered around a main provincial road, with several pockets of secondary vegetation (Fig. 13A) and some areas  13D), with usually 2-5 individuals present on the same plant. Daytime search revealed the presence of fewer individuals, mainly juveniles at different nymphal stages. Searching over a wide area, we noted that the distribution of the species on host trees was markedly discontinuous, with individuals concentrated on single larger plants and apparently absent from Ficus trees in the immediate vicinity.
Eggs were dropped to the ground and needed ca. 40 days to hatch at 23 °C. Newly hatched nymphs were reared to adulthood using the hauili tree (Ficus septica) or stinging nettle (Urtica dioica) as food plants. Under rearing conditions, the nymphal development lasted for ca. 60 days, and the average life span for males was ca. 45 days compared with ca. 140 days for females. The insects were active both during the day and night.
The mating was observed under rearing conditions. On day before the final moult, the subadult female starts to be guarded by 3-4 competing males, usually with one male mounted on the female's back and facing into the same direction as the female. Copulation starts immediately after the female has completed the last nymphal moult. Generally, we found that when presented with a receptive virgin female, the male quickly mounts her and starts a series of abdominal bending movements apparently searching for the appropriate mating position. The female curve the abdominal tip upwards thereby exposing her terminalia, while the male bends its abdomen on the left side with his terminalia directed forward. The clasping cerci of the male grasp the female at the base of her eighth sternum, and at the same time a bulb-like phallic organ comes into contact with the female genitalia (Fig. 14). Copulation lasted approximately three hours. The presence of a spermatophore has not been ascertained. Mated females showed an aggressive behaviour towards potential mates, and multiple matings were rarely observed. They chase away approaching males through quivering movements of the body, beating legs on the substrate, and flashing their wings for a few seconds. This behaviour is also practiced by resting individuals when disturbed by conspecifics.
If threatened, adults and nymphs of O. kangi sp. n. spray a milky defensive secretion from the prothoracic exocrine glads and inevitably let themselves fall to the floor and quickly run away.

Taxonomic notes on some species of Orthomeria (Orthomeria)
During our comparative analysis of the type material and additional specimens of Orthomeria spp., we recognised that Orthomeria catadromus (Westwood, 1859) represents a junior synonym of O. pandora (Westwood, 1859), syn. n. Both species were published in the same publication (Westwood 1859), but O. pandora has page priority. The type series of O. catadromus consists of three syntypes, two of them in BNHM and one in UMO. A specimen in BNHM bearing the following data is here designated as lectotype: the locality Sumatra was handwritten by Westwood on the identification label under Aschiphasma catadromus; the specimen has a white database label with the code BMNH(E) #845139. There is no separate label with a locality, however there is a small round grey label with a question mark. Although O. catadromus was originally recorded from Sumatra, there is reasonable doubt that this is in error, and subsequent reports of this species refer only to the Philippines (Bruner 1915, Bragg 2001. In fact, various species described by Westwood have doubtful locality data and several have since been recorded from different localities. Another example concerning the Philippine phasmid fauna is that of Theramenes olivaceus (Westwood, 1859), a species of Eubulidini (Heteropterygidae: Obriminae) originally described from Sri Lanka, but afterwards recorded from the Philippines (Bruner 1915) in accordance with the fairly restricted distribution of the tribe, not including Sri Lanka and continental Asia.
A lectotype is here designated also for O. pandora (Westwood, 1859). The original syntype series in BMNH originates from different localities. Two specimens originate from the Philippines and a third one from "ceram". The specimens from the Philippines do not bear more precise data than "Philippine Islands". The specimen from the Philippines still having one of its forelegs is hereby designated as lectotype.
Identification key to the species of Orthomeria (Orthomeria)

Phylogenetic interpretation of morphological characters
O. kangi sp. n. shows some phylogenetically informative characters that are helpful to find its placement among the subgroups of Euphasmatodea. The unbranched radial vein (= absence of the radial sector), the undivided sternum 9 and the incurved cerci with an apical spine or tooth in the male, represent key synapomorphies of Aschiphasmatidae (Bradler 2009). The latter specialized character is definitely homologous with the sharp blade-like ridge found in the male cerci of the new species. O. kangi sp. n. also shows distinctly pectinate claws, a putative derived character of the tribe Aschiphasmatini (Aschiphasmatidae excluding Dajaca) (Bragg 2001, Bradler 2009). Within Aschiphasmatidae, a brightly coloured (yellow, orange, or red) costal region of the hind wings occurs only in Orthomeria. This character can be interpreted as an autapomorphy that provides evidence for the monophyly of the genus. Attachment structures of Aschiphasmatidae has been previously analysed in Dallaiphasma eximius (Gottardo 2011b). A feature shared between this species and O. kangi sp. n. is the absence of an euplantula on tarsomere V. In Timema, a small euplantula is present on the distal tarsomere (Beutel and Gorb 2008). Within Euphas-matodea the condition appears variable: the euplantula is present and generally small compared to the size of tarsomere V in Eurycantha calcarata and Conlephasma enigma Heller 2012, Gottardo et al. 2015), while it is absent in several taxa including Carausius morosus, Medauroidea extradentata, Ophicrania conlei, and Hermarchus leytensis (Gottardo 2011a, Bußhardt et al. 2012, Gottardo and Vallotto 2014. The two species of Aschiphasmatidae have also smooth euplantulae on tarsomeres I-IV. Interestingly, while D. eximius has a honeycomb micropattern, O. kangi sp. n. shows only faint microgrooves on the contact surface. It has been hypothesized that nubby euplantulae covered with acanthae are a groundplan feature of Phasmatodea (Beutel and Gorb 2008), implying secondary modification of these surface structures in Aschiphasmatidae. It would be interesting to analyze the attachment structures of additional species of Aschiphasmatidae, since the character system could be more diverse within the family.
The male terminalia of O. kangi sp. n. show a number of specific modifications. An unusual feature is the complete absence of clasping devices (the tergal thorn pads) on the hind margin of the tergum X. Within Aschiphasmatidae these structures have been described in D. eximius as a single row of ca. 12 tooth-like projections (see Gottardo 2011b: fig. 5), and are usually present and well developed in Euphasmatodea (Bradler 2009). However, they are absent for example in Timema, Agathemera, in the taxon Sermyleformia sensu Bradler (2009), and their secondary loss has been established in extant leaf insects (partim) (Wedmann et al. 2007). It is conceivable that in O. kangi sp. n the reduction of tergal thorn pads has been compensated by the acquisition of the specialized cerci, that together with the vomer form the male clasping organs of this species. The structure of male terminalia has been described here in detail for the first time in Orthomeria, and for future studies these characters may represent important diagnostic features of males of species of this genus, as also exemplified in other euphasmatodean taxa by Bradler (2009) and Buckley et al. (2014).

Intraspecific morphological variations
The captive rearing showed the presence of substantial intraspecific colour variation in the females of O. kangi sp. n. All wild individuals, both males and females, had the chromatic characters of the typical black colour morph. When the species was reared at cool temperatures (ca. 16 °C) all females developed the brown colour morph, while males were invariably black. Interestingly, the offspring of the brown females reared at warmer temperatures (ca. 23 °C) consisted of only black females.
A certain amount of variation was found also as to the length of the hind wings of females, regardless of the two colour morphs. In some females the hind wings reach the hind margin of the abdominal segment IV, whereas in other they can extend up to the hind margin of segment V. Intraspecific trends of variation in wing length have been rarely documented in Phasmatodea. A different example is that of Asceles margaritatus Redtenbacher, 1908 (Necrosciinae), where two separated macropterous and micropterous forms involving both sexes have been described (Bragg 2002).