Tetramorium bicarinatum species group

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This is a widely ranging group and has been part of taxonmic treatments in three different areas: the Afrotropical region (Bolton 1980), the Malagasy region (Hita-Garcia and Fisher 2011), and India Agavekar et al. 2017).

Diagnosis and Species

Bolton (1980)

Afrotropical

bicarinatum species complex

cristatum species complex

emeryi species complex


Key to species of the Afrotropical Tetramorium bicarinatum species group

Antennae with 12 segments. Sting appendage triangular, dentate or pennant-shaped. Anterior clypeal margin with a median notch or impression. Median portion of clypeus usually with three strong longitudinal carinae, often without other sculpture but sometimes with extra, more feeble carinae or rugulae present (carinae reduced in Tetramorium emeryi and Tetramorium erectum). In African species the median portion of the clypeus marginate laterally, especially in larger species, the margination of a raised rim or flange which runs to the anterior clypeal margin and posteriorly is continuous with the frontal carinal lobes and thus with the frontal carinae themselves. Mandibles smooth in all African species except the introduced bicarinatum. Frontal carinae strongly developed, dorsally with a raised rim or flange, reaching back almost or quite to the occipital margin. Propodeal spines usually strongly developed (not in T. emeryi), straight or somewhat upcurved along their length. Petiole nodiform. First gastral tergite commonly with basal costulae. Basic sculpture throughout the group is a strong rugoreticulum. Pilosity usually abundant on all dorsal surfaces of the body, the hairs long and strong; short, truncated hairs absent. Middle and hind tibiae equipped with numerous short but quite strong hairs which are subdecumbent to decumbent.

Malagasy region


Key to Malagasy Tetramorium species groups

Hita-Garcia and Fisher (2011) - 12-segmented antennae; anterior clypeal margin with distinct median impression; frontal carinae well-developed, ending shortly before or reaching posterior head margin; anterior face of mesosoma only weakly developed and rounding onto the dorsum; margination between lateral and dorsal mesosoma weak; propodeal spines medium-sized to long and spinose; propodeal lobes triangular to elongate-triangular, acute, and short to medium-sized; petiolar node nodiform, longer than high or as long as high, in two species posterodorsal angle higher situated than anterodorsal; postpetiole roughly rounded; mandibular sculpturation variable; cephalic sculpturation strongly developed, mostly reticulate-rugose, between frontal carinae close to posterior clypeus more rugose, ground sculpturation of head generally faint or absent; mesosoma and waist segments reticulate-rugose; first gastral tergite in some species with basigastral costulae, rest of the gaster unsculptured, smooth, and shiny; all dorsal surfaces with long, erect hairs; sting appendage triangular.

India


Key to Tetramorium of India

Agavekar et al. (2017) - Twelve-segmented antennae; anterior clypeal margin notched and unspecialized; eyes moderately sized to large; antennal scapes short to moderately long, not surpassing posterior head margin; antennal scrobes usually present, but shallow and not clearly defined posteriorly and ventrally; frontal carinae always strongly developed and reaching posterior head level; base of first gastral tergite not concave in dorsal view, without tubercles or teeth on each side; pilosity on dorsal surfaces of body erect with long and fine hairs; sting appendage dentiform.

Notes

Afrotropical

Bolton (1980) - The Ethiopian region has nine native species and one introduced species described to date in this group. The bicarinatum-group is also strongly represented in the Oriental and Indo-Australian regions where 13 species are now known (Bolton, 1977; 1979), but endemic species of the group are absent from Australia and Madagascar. Two of the South East Asian species, Tetramorium insolens and Tetramorium bicarinatum, are accomplished tramps, and the second of them has been found (but only once) in South Africa where it was imported with some orchids from Burma.

The nine endemic African species fall into three species-complexes on morphological grounds, particularly on the construction of the petiole. The first of these, containing the species Tetramorium emeryi and Tetramorium erectum, is restricted to South Africa and is characterized by a large size (HW > 0-80) and by having the petiole node bluntly nodiform (Figs 47, 51) with rounded or blunted antero- and posterodorsal angles. The node itself is quite high and tends to narrow slightly from base to apex. Basigastral costulae tend to be few and weak and the spaces between them are shagreened or finely punctulate. The two members of this complex are also fairly well characterized within the group by the condition of the propodeal spines, which are reduced to minute teeth in emeryi and are strongly elevated in erectum, often having their apices directed vertically.

The second complex contains the three closely related species Tetramorium cristatum, Tetramorium gazense and Tetramorium notiale. Of these three T. cristatum is mostly confined to the forested or wooded parts of the northern half of the continent, ranging from Sudan to Zaire and from Ghana to Uganda. The second species has been found in southern Zaire, Rhodesia and Tanzania and T. notiale is predominantly a species of the southern half of the continent, ranging from Zaire to South Africa. The species are quite large (HW always > 0.70 and usually > 0.80) and have a petiole node which is roughly rectangular in profile (Fig. 49) with sharp, usually roughly right-angular antero- and posterodorsal angles. Basigastral costulae are sharply defined, fine and dense. The sculpture of these species is a dense, coarse rugoreticulum which extends dorsally from the occiput to the postpetiole. Differentiation of the species lies primarily upon their colouring, as discussed under T. gazense. The third and final complex contains the four smaller species of the group (Tetramorium amentete, Tetramorium peutli, Tetramorium phasias, Tetramorium pullulum) which in general have HW < 0.70, rarely greater. The petiole node in profile is long and low (Figs 48, 50), with a projecting posterodorsal angle and with a tendency for the posterior face to be slightly longer than the anterior so that the dorsum is higher behind than in front. Development of basigastral costulae is variable in the complex but they are usually present. At present T. amentete is only known from West Africa, T. peutli and T. pullulum are widely distributed in West and Central Africa but T. phasias appears to be restricted to the southern part of the continent. Both T. amentete and T. phasias are strongly sculptured species, with a rugoreticulum which extends from occiput to postpetiole, whilst T. peutli and T. pullulum are less strongly sculptured, always with extensive shining areas and with the postpetiole dorsum not or only very feebly sculptured. As mentioned above, T. bicarinatum has been found once in Africa, as an introduction from South East Asia. This species is easily distinguished from the native African forms as it has sculptured mandibles whereas all the endemics have the mandibles smooth and shining with scattered small pits.

India

Agavekar et al. (2017) - This is a relatively species-rich group with 16 species in the Indomalayan and Australasian regions and nine in the Afrotropical region. At present, the group is represented in India by five species, of which two are global tramps. It is challenging to ascertain if these ants are native members of the Indian myrmecofauna or introduced. The taxonomy of the group on the whole is complicated and identifications with the currently available resources are often challenging. In parts this is also true for the Indian species. The species delimitations of Tetramorium indicum, Tetramorium pacificum, and Tetramorium scabrum are not clear and misidentifications can occur easily. The identity of Tetramorium petiolatum is even more doubtful. Its original description is of comparatively poor quality and the authors state that the species is close to T. pacificum (Sheela & Narendran, 1998). However, based on their line drawings it looks very much like Tetramorium bicarinatum and Tetramorium indicum. Since the type material is not available for examination the true identity of this species will remain obscure.

Malagasy region

Hita-Garcia and Fisher (2011) - The T. bicarinatum group is represented in the Malagasy region by three species only, all being tramp species with wide distribution ranges. Tetramorium bicarinatum, Tetramorium insolens, and Tetramorium pacificum are most certainly not native to the Malagasy region and seem to have their native ranges in the Oriental and Indo-Australian regions (Bolton, 1977, 1979; McGlynn, 1999). Tetramorium bicarinatum is the most common of the three and can be found in many localities in Madagascar and its surrounding islands, whereas T. insolens and T. pacificum have not yet reached mainland Madagascar. Tetramorium insolens is only known from Mauritius and Reunion (Blard et al., 2002; Roberts & McGlynn, 2004) while T. pacificum occurs in the Seychelles and Mauritius.

In the Malagasy region, this group cannot be confused with another group with 12-segmented antennae since it is the only one with a medially impressed anterior clypeal margin. Within the species group, the three species can be morphologically well-separated by comparing the shape of the petiolar node, mandibular sculpturation, pilosity, and colouration.

Additional Resources

References