A new ant species, Paraparatrechina neela sp. nov., with a captivating metallic-blue color is described based on the worker caste from the East Siang district of Arunachal Pradesh, northeastern India. This discovery signifies the first new species of Paraparatrechina in 121 years, since the description of the sole previously known species, P. aseta (Forel, 1902), in the Indian subcontinent.

Abor Expedition, Arunachal Pradesh, aspirator, East Siang, taxonomy

The formicine ant genus Paraparatrechina was originally described by Donisthorpe (1947) as a subgenus of Paratrechina Motschoulsky, 1863, with Pa. (Paraparatrechina) pallida (Donisthorpe, 1947) as type species by monotypy. Later, Brown (1973) treated Paraparatrechina as a provisional junior synonym of Paratrechina, and Trager (1984) confirmed this synonymy, citing the lack of monophyly of the subgenus based on a morphological assessment. However, LaPolla et al. (2010a) redefined Paratrechina as a monotypic genus with Pa. longicornis (Latreille, 1802) based on a phylogenetic analysis of the Prenolepis genus-group. That study also recovered Paraparatrechina as a valid monophyletic genus, distinguishable from its sister taxa by the uniform, erect setal pattern on the mesosoma. Currently, the Prenolepis genus-group comprises the genera Euprenolepis Emery, 1906, Nylanderia Emery, 1906, Paraparatrechina, Paratrechina, Prenolepis Mayr, 1861, and Pseudolasius Emery, 1887 (LaPolla et al. 2010a).

Paraparatrechina are generally small ants, measuring 1–2 mm long, and they are typically found in the Afrotropical, Australasian, Indomalayan, Oceanian, and Palearctic biogeographic regions (LaPolla et al. 2010b; AntWeb 2023a). The genus can be easily distinguished from other formicine ant genera by a unique mesosomal setal pattern, which includes two pairs of erect pronotal setae, one pair of mesonotal setae, and one pair of propodeal setae (LaPolla et al. 2010a). The genus is often confused with Nylanderia. However, Nylanderia lacks a pair of erect propodeal setae and has six mandibular teeth instead of five (LaPolla et al. 2010b).

Paraparatrechina is present in various tropical environments, ranging from rainforests to forest clearings, and can be found in a wide spectrum of habitats, ranging from leaf litter on the ground to high up in the canopy (LaPolla et al. 2010b). Afrotropical species, for example P. weissi (Santschi, 1910) and P. bufona (Wheeler, 1922), are the only known polymorphic species of Paraparatrechina, displaying several morphological characteristics indicative of a hypogaeic lifestyle (LaPolla et al. 2010a).

Currently, Paraparatrechina encompasses 38 valid species and four valid subspecies (Bolton 2023). The Indomalayan biogeographic region has 14 known species, while P. aseta (Forel, 1902) is the only known species in the Indian subcontinent until now (Bharti and Wachkoo 2014). This species has been reported in several states of India, including Gujarat, Himachal Pradesh, Jammu and Kashmir, Sikkim, Nagaland, and West Bengal (Bharti et al. 2016; Janicki et al. 2016; Guénard et al. 2017). In this study, we describe and illustrate P. neela sp. nov., which was discovered in the foothills of the Eastern Himalayas of India. This find comes 121 years after the discovery of the only previously known Indian species, P. aseta.

During the period of colonial rule in India, a scientific expedition to document the natural history and geography of the Siang Valley of the Eastern Himalayas accompanied a punitive military expedition against the indigenous people there in 1911–12 (Army Intelligence Branch 1911). Originally known as the Abor Expedition, the findings of the expedition were published in several volumes from 1912 to 1922 in the Records of the Indian Museum. Now, a century later, a team of researchers has been engaged in a series of expeditions under the banner “Siang Expedition”, funded by the National Geographic Society through the wildlife-conservation expedition grant (NGS-71945c-20), to resurvey the biodiversity of the region. In May 2022, among several other ant species from various genera, we collected two worker specimens of P. neela sp. nov. from Yingku village, in East Siang District of Arunachal Pradesh, northeastern India. This remarkable new species represents the first documented occurrence of the genus in Arunachal Pradesh and only the second Paraparatrechina species known from the Indian subcontinent.

Two worker specimens belonging to Paraparatrechina were collected from a secondary forest at an elevation of 803 m in Yingku village, which is located in East Siang District of Arunachal Pradesh, northeastern India (Fig. 1). East Siang District is encompassed between latitudes 27°43'N to 29°20'N and longitudes 94°42'E to 95°35'E and has an area of 4005 km². It has tropical and humid-subtropical climate, with temperatures of 18–28 °C and an average annual rainfall of 4168 mm (Yumnam et al. 2013; Yogesh Kumar et al. 2022). These specimens were collected from debris in a hole in a tree trunk 3 m above the ground. We used an aspirator to extract the specimens and preserved them in absolute alcohol. The specimens were point mounted and examined under a Zeiss SteREO Discover.V8 microscope.

Figure 1. 

Map showing the type locality of P. neela sp. nov. in the Yingku Village, Arunachal Pradesh, northeastern India A India, with the North East Region (NER) shown in gray B states of the NER with type locality in Arunachal Pradesh C Arunachal Pradesh showing the location of the type locality (Yingku village) D Google Earth satellite image showing the type locality (Source: Google Earth Pro 2023, accessed on 11 February 2024).

The identifications of the specimens were made by referring to available taxonomic keys by LaPolla et al. (2010a, 2010b) and comparing them with images of the types of all known Paraparatrechina species, except for P. bufona, P. kongming (Terayama, 2009), P. nana (Santschi, 1928), P. sakuya Terayama, 2013, P. sordida (Santschi, 1914), and P. tapinomoides (Forel, 1905), which are not available on AntWeb (2023a). We checked original descriptions and available illustrations for specimens that did not have type images. The unique metallic-blue coloration of the body, in combination with the head shape, sculpture and pubescence patterns, helped us to confirm the status of new species. Stacked focus montage images of the new species were captured at 200× magnification using a Keyence VHX 6000 digital microscope. Final figures were prepared using Adobe Photoshop v. 25. The map was prepared using ArcGIS v. 10.4.1 (ArcGIS 2023). The holotype and paratype specimens are deposited in ATREE Insect Museum, Bangalore, India (AIMB). Body measurements are in millimeters and were taken with AxioVision v. 4.8 software (Carl Zeiss, Germany) and recorded with two decimal places. Body measurements and indices (Fig. 2) follow LaPolla and Fisher (2014).

Figure 2. 

Paraparatrechina umbranatis LaPolla & Cheng, 2010, showing schematic representation of the body measurements. Abbreviations are defined in materials and methods. Photo credit: April Nobile, www.antweb.org, CASENT0178764 (AntWeb 2024).

Eye length (EL): maximum length of compound eye in full-face view.

Head length (HL): the length of the head proper, excluding the mandibles;

measured in full-face view from the midpoint of the anterior clypeal margin to a line drawn across the posterior margin from its highest points.

Head width (HW): the maximum width of the head in full-face view.

Scape length (SL): the maximum length of the antennal scape excluding the condylar bulb.

Pronotal width (PW): the maximum width of the pronotum in dorsal view.

Weber’s length (WL): in lateral view, the distance from the posteriormost border of the metapleural lobe to the anteriormost border of the pronotum, excluding the neck.

Gaster length (GL): the length of the gaster in lateral view from the anteriormost point of the first gastral segment (third abdominal segment) to the posteriormost point.

Total length (TL): HL + WL + GL.

Cephalic index (CI): (HW / HL) × 100.

Relative eye length index (REL): (EL / HL) × 100.

Scape index (SI): (SL / HW) × 100.

Paraparatrechina is a relatively underexplored genus but with an expected species diversity much higher than what is currently known (LaPolla et al. 2010b; LaPolla and Fisher 2014). Previous studies indicate that the Prenolepis genus-group, which includes Paraparatrechina, originated and diversified during the late Paleocene and Eocene, between 45 and 60 mya (Blaimer et al. 2015; Matos-Maraví et al. 2018). Blaimer et al. (2015) estimated ancestral crown age of the genus ranges from 26.8 to 31.4 Ma. Similarly, the estimated crown age of a clade within Paraparatrechina is 23.5 Ma (Matos-Maraví et al. 2018). Matos-Maraví et al. (2018) suggested that the Prenolepis genus-group most likely originated in continental Southeast Asia. It points to the possibility of dispersal and colonization of this group from Southeast Asia to India. Further explorations are imperative to unravel the influence of the Himalayas and the Western Ghats on this group’s evolution and dispersal.

Paraparatrechina species are typically found at elevations below 800 m, although a few inhabit elevations around 1500 m (AntWeb 2023a). However, a few species, such as P. minutula (Forel, 1901) and P. kongming (Terayama, 2009), are known to occupy higher elevations above 2000 m (2300 m and 2500 m, respectively). Paraparatrechina neela sp. nov. was collected from an elevation of 803 m. This species showcases a unique metallic blue coloration not observed in any other species within this genus. However, some Paraparatrechina species do exhibit color reflections or iridescence, like P. iridescens (Donisthorpe, 1942).

Blue coloration in animals, except in marine sponges, is a relatively rare phenomenon. However, there are several blue species of vertebrates, like fish, frogs, and birds, as well as invertebrates, such as spiders (Bagnara et al. 2007; Doucet and Meadows 2009; Umbers 2013; Chomphuphuang et al. 2023). While blue coloration is common among many insects, particularly in hymenopterans such as Apoidea, Chrysididae and Ichneumonidae, it is very rare in Formicidae. Blue colour in insects is usually produced by the arrangement of biological photonic nanostructures rather than pigments, and it has independently evolved in various groups (Prum 1999; Seago et al. 2009; Hsiung et al. 2015; Chomphuphuang et al. 2023). This vibrant feature raises intriguing questions. Does it help in communication, camouflage, or other ecological interactions? Delving into the evolution of this conspicuous coloration and its connections to elevation and the biology of P. neela presents an exciting avenue for research.

We are grateful to Ganesh N Shinde for helping us to prepare the maps. We extend our profound gratitude to Dr Ranjith, A.P., Dr John S. LaPolla, Dr Andrea Lucky, and Dr Jason Williams for their invaluable insights while preparing this manuscript. We express our sincere gratitude to Dr Jeffrey Sosa Calvo, Dr Peter Hawkes, Dr Rodolfo Probst, and an anonymous reviewer for their constructive and insightful comments and suggestions on our manuscript.