Dolichoderus cuspidatus species group

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Based on Dill 2002.

Species

Distribution

Distribution exactly matches the distribution of the mealybug tribe Allomyrmococcini, which comprises the specific trophobiotic partners of the herdsmen ants. The distribution pattern seems to be closely connected to the primary winglessness of the queens and the fact that sociotomy is the mode of colony reproduction. This only allows dispersal by land.

Migrating herdsmen symbioses were found on the three Greater Sunda Islands Borneo, Java and Sumatra, on the Malay Peninsula and in Thailand.

The distribution extends westwards to the Mentawai Islands, north-east to Laos and Vietnam, and north via Myanmar (Burma) and Northeastern India (Manipur) to the Himalayas (Sikkim). For collections of Dolichoderus feae from Sikkim associations are recorded with four or five species of Aphidoidea ( Datta et al. 1983, Manmohini Devei et al. 1987). Whether there are additional associations with Allomyrmococcini or whether D. feae exists there without Allomyrmococcini, as in some montane populations of Dolichoderus erectilobus and Dolichoderus tuberifer, can not be verified from these publications. From the area east of the Wallace Line, there are neither relevant existant collections of the ants nor the pseudococcids, nor could migrating herdsmen be found during a specific search on Sulawesi. West of the Wallace Line, i.e. on the area of the Sunda Shelf, Bali was the on ly place where migrating herdsmen could not be found, despite an extensive search.

The highest number of sympatric migrating herdsmen species is found on Borneo (in Poring, Sabah, alone exist five syntopic migrating herdsmen systems), followed by Sumatra, Thailand and the well-surveyed Malay Peninsula (Malaysia).

Records from the perhumid parts of the distribution area with extensive evergreen lowland rain forests (Borneo, Malay Peninsula, Sumatra) come from all altitudes up to 2,300 m a.s. l., while in Java and especially in the more seasonal monsoon areas north of the Isthmus of Kra, the distribution seems to be concentrated mainly on the mountainous areas with evergreen montane forests.

Most of the collection sites were situated at the edges of primary or species-rich secondary forests or in forest gaps. This may be partly caused by a more intense search along tracks and roadsides partly because the secondary growth and pioneer vegetation of these areas is a favourable source of food for the Pseudococciclae (see chapter V.3.7). Nevertheless, some colonies have been found deep within primary forests. The trails of these colonies usually disappeared into the canopy, suggesting that the species in primary forests are predominantly living there. This is supported by findings in the high canopy at the ca. 40m high Canopy Walkway in Pori ng, Sabah (cuspidatus, magnipastor).

Identification

Key to Dolichoderus cuspidatus group workers

The cuspidatus group is a species-rich group, comprising 15 species. Although there is a remarkable variation, particularly in some striking characters such as the existence of spines or cornicles on mesonotum or propodeum, the group is well defined. Particularly through the inclusion of morphological characters of females and males, it is distinct and easily separable from all other Oriental species groups.

The cuspidatus group can be defined by the combination of the following characters:

  • Head, antennae, femora, tibiae as well as dorsal surface of alitrunk, petiole and gaster of all castes are usually completely void of erect hairs. The single exception is pilinomas whose workers are moderately pilose, whose queens have few erect hairs, and whose males have none.
  • The queens (known in cuspidatus, erectilobus, gibbifer, kinabaluensis, maschwitzi, pastorulus, pilinomas, tuberifer) are wingless. At most, there are vestigial remnants of wing-buds. In any case they have fused mesonota. If the scutum area is still recognizable by the outline of the mesonotum, the scutum-alitrunk-index (ScI) is much smaller than in winged species groups (figs. III-79, III-80). The ocelli are lacking or show different degrees of reduction.
  • The colonies are, as far as known, strictly monogynous.
  • The queens are usually physogastric. Their petiole is, in relation to the alitrunk (e.g. PtW/PpW), usually wide (figs. III-78, III-80).
  • The males (known in cuspidatus, kinabaluensis, maschwitzi, pastorulus, pilinomas, and tuberifer) usually have large compound eyes, in particular wider than in other species groups. Although the indices OI and OI2 (which are based on the eye length) of those species with the relatively smallest eyes (maschwitzi and kinabaluensis) fall within the range of the thoracicus group, the width-based eye indices (OI3, OI4) of all cuspidatus group species lie always above those of the thoracicus group (figs. III-81, III-82, III-84, III-85).
  • Many species have a ± distinct superoccipital pit, at least in some populations.
  • All available biological data indicate a highly specialized migrating herdsmen lifestyle with very similar biological and ethological patterns, such as a strongly developed transport of trophobiotic partners, bivouac-like nests and a highly species-specific association with mealybugs of the tribe Allomyrmococcini. However, so far there are no data available about the biology and trophobiotic associations of brevithorax and modiglianii.

In addition, the workers can be separated from those of the monoceros, scabridus, and sulcaticeps species groups by further characters, such as the shape of the head (posterior margin more concavely curved and CI smaller than in sulcaticeps group [figs. III-72, III-74, III-76]), the scapus index, SI (smaller than in scobridus group [figs. III-73, III-74]); the shape of the alitrunk (propodeum usually narrower than in sulcaticeps group, AWI higher [figs. III-75, III -76]), the shape of the petiole and the surface sculpturing (see respective diagnoses of these groups).

However, the strongest morphological similarity exists between workers of the cuspidatus and the thoracicus species groups. These two groups are particularly similar regarding the shape of head, alitrunk and petiole node as well as in respect of sculpturing and pubescence. In addition to the above-mentioned general diagnostic characters, the two groups differ mainly in the body size, although a zone of overlapping exists (fig. III-72: HW). Yet, the workers as well as the sexual castes of most species of the cuspidatus group (except pilinomas) can easily be separated from the thoracicus group by the lack of the dorsal pilosity. Also, the males of the cuspidatus group, in addition to the larger size of their eyes, seem to differ from the thoracicus group by longer mandibles (figs. III-83 to III-85). However, this observation is based only on a relatively small number of examined species of the thoracicus group (five), and therefore, it is uncertain whether this character applies to the group as a whole.

Description

Worker

(figs. III-2 to III-18): Moderate to large sized species (HW 0.98-2.08 mm, AL 1.41-2.66 mm, TL 4.18-7.70 mm). Colour variable (light yellow-brown, red-brown to black). Head, alitrunk, and petiole microscopically usually imbricate, appearing as finely and densely reticulate or punctured at lower magnification (up to 125X); in some species, in addition to this micro-sculpturing, head and alitrunk (particularly dorsal face of mesonotum and propodeum) coarsely wrinkled (areolate- rugose) (e.g. figs. III-62, III-64 to III-66). Head, antennae, and tibiae, as well as dorsal face of alitrunk, petiole, and usually of gaster in most species completely void of erect hairs (except pilinomas); pilosity restricted to the end of gaster (4th tergite) and to ventral side of gaster, petiolus, coxa and trochanter. Body surface usually ± strongly pubescent, very rarely (e.g. some coniger specimens) ± bald; pubescence particularly dense on gaster, usually tufted; pubescence of gaster often in form of paired cowlicks with a median parting, which can appear macroscopically as a light grey or golden yellow striping. Posterior margin of head, in full face view, always distinctly ± deeply concavely emarginate and ± sharp-edged; often with a ± distinct pit, for which the term “superoccipital pit” is introduced (e.g. figs. III-60a, III -62a, III-66a); CI 70-114; SI 66-115; OI 17-31. Mesonotum ± convex, often median depressed, in some species (brevithorax, cuspidatus, furcifer) armed with a pair of dorsolaterally pointed spines; mesonotum usually distinctly longer than wide; promesonotal suture always distinct, posterior margin towards metanotum often indistinct or effaced. Propodeum ± rising high, its lateral edges sometimes lobiformly expanded, in some species forming distinct ± stout (brevithorax, furcifer, erectilobus, laotius) or long and slender (coniger, cuspidatus, magnipastor) cornicles or spines; posterior edge of basal surface of propodeum usually sharp-edged and may or may not project over the concave declivity. Propodeum (including metapleura) usually distinctly narrower than pronotum (AWI 117-161). Petiole node in dorsal view usually compressed, i. e. distinctly broader than long, dorsal edge entire or ± distinctly emarginate. Basal part of first gastral segment usually lighter coloured, often with yellow dots, often median with shallow furrows which are arranged ± cross- like or star- like. Otherwise showing the characters typical for the genus (see Shattuck 1992: 67).

Queen

(known of cuspidatus, erectilobus, gibbifer, kinabaluensis, maschwitzi, pastorulus, pilinomas and tuberifer) (figs. III-19 to III-25, III-67 to III-70): Wingless, ± ergatoid queens; head and alitrunk slightly larger than in workers, particularly mesonotum distinctly wider; sculpturing and lack of pilosity similar to workers; only pilinomas with sparse pilosity on alitrunk surface (but still lacking erect hairs on dorsal surface of head); pubescence usually more dense than in workers. Head usually slightly wider than long, usually wider than in workers (CI 95- 115); existence and development of ocelli vary significantly inter- and intraspecifically from a complete lack to the presence of one, two or three well developed ocelli. Mesonotum significantly larger than in workers, but always completely fused; never separated by sutures into scutum, prescutellum and scutellum as in a typical flight thorax; in some cases, this division can still be recognized by the outline of the mesonotum; in that case, the “scutum” portion is relatively small (ScI < 35); parapsidal furrows lacking. Wings always lacking; some specimens (intraspecifically variable) with vestigial remnants of wing-buds or tegulae of forewing and/or hindwing (figs. III-69b-c, III-70b-c); metanotum well defined, anepisternum, katepisternum and metapleuron somewhat less distinctly so. Alitrunk structures like spines and cornicles always less distinctly developed than in workers. Node of petiole compressed and very wide (PtW 0.51-1.24 mm). Often, particularly in species with large colonies (e.g. cuspidatus, kinabaluensis, tuberifer), strongly physogastric (length of gaster, measured on specimens freshly taken out of 75 % ethanol: 2.25-5.32 mm).

Male

(known of cuspidatus, kinabaluensis, maschwitzi, pastorulus, pilinomas, and tuberifer) (figs. III-26 to III-31): Typical Dolichoderus males (see Shattuck 1992:70). Body surface ± strongly pubescent, but dorsal surface always completely void of erect hairs. Mandibles usually long (MdL 0.23-0.47 mm), the masticatory margin usually distinctly longer than clypeus (MdCI 107- 170). Compound eyes usually large (OI 42-52; OI2 50-70; 0I3 31-41; OI4 38-58). Ocelli well developed. First funiculus segment very small, barely longer than wide, 2nd funiculus segment almost as long as scape, 3rd to 11th segment shorter and ± regular, 12th segment somewhat longer and tapering off towards the tip. Alitrunk with typical flight thorax. Wings usually slightly fumeous-brownish and pubescent; forewing with a ± square discoidal cell and two cubital cells. Subgenital plate strongly concave to v-shaped.

Herdsmen

The species of this group are all believed to possess a highly specialized migrating herdsmen lifestyle that includes: a strongly developed transport of trophobiotic partners, bivouac-like nests and a highly species-specific association with mealybugs of the tribe Allomyrmococcini.

In species-specific associations with the ants of this species group, we found 25 different species of mealybugs, belonging to 10 different genera within the tribe Allomyrmococcini. Eighteen of these species and six genera are new to science. There are 35 different systems of symbiosis between species of the Dolichoderus cuspidatus group and species of Allomyrmococcini known to date.

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References