Journal of Threatened Taxa | www.threatenedtaxa.org | 26 March 2022 | 14(3): 20780–20785

ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)

https://doi.org/10.11609/jott.6962.14.3.20780-20785

#6962 | Received 03 December 2020 | Final received 09 October 2021 | Finally accepted 15 March 2022

Two new species of army ants of the Aenictus ceylonicus group (Hymenoptera: Formicidae) from Kerala, India

Anupa K. Antony¹ & G. Prasad²

^1,2Department of Zoology, University of Kerala, Kariavattom, Thiruvananthapuram, Kerala 695581, India.

¹shininglantern90@gmail.com (corresponding author), ²probios1@gmail.com

ZooBank: urn:lsid:zoobank.org:pub:B71660E3-65E0-4F47-A2B1-38E823B1AB38

Editor: Anonymity requested. Date of publication: 26 March 2022 (online & print)

Citation: Antony, A.K. & G. Prasad (2022). Two new species of army ants of the Aenictus ceylonicus group (Hymenoptera: Formicidae) from Kerala, India. Journal of Threatened Taxa 14(3): 20780–20785 . https://doi.org/10.11609/jott.6962.14.3.20780-20785

Copyright: © Antony & Prasad 2022. Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use, reproduction, and distribution of this article in any medium by providing adequate credit to the author(s) and the source of publication.

Funding: CSIR-UGC.

Competing interests: The authors declare no competing interests.

Acknowledgements: We are grateful to Manoj vembhayam, member, TNHS for his support and guidance.

Abstract: The genus Aenictus Shuckard is a diverse group of army ants in the Old World tropics and subtropics. Herein, two new species from India (Aenictus kodungallurensis and Aenictus malakkaparensis) belonging to Aenictus ceylonicus group were discovered from Kerala, India. An updated key to the Aenictus ceylonicus species group from southern Asia is presented.

Keywords: Coastal area, Dorylinae, elevation, hand picking, Kodungallur, Malakkapara, taxonomic analysis, Thrissur.

Aenictus Shuckard 1840, belonging to the subfamily Dorylinae of the family Formicidae, is one of the true army ant genera occurring throughout Africa and in tropical and subtropical areas from India, Middle-east, southern China, Taiwan, Japan, Afghanistan, Armenia, southern Asia to New Guinea and Australia (Gotwald 1995; Shattuck 1999, 2008; Jaitrong & Yamane 2013). The genus Aenictus Shuckard, is the most diverse among all 18 genera of the monophyletic army ant subfamily Dorylinae (Brady et al. 2014) with 187 valid species and 30 valid subspecies (Bolton 2020). In the present paper we deal with the largest species group, the Aenictus ceylonicus Mayr group that has been revised in detail by Jaitrong & Yamane (2013). The group contains 23 species distributed in southern Asia. Two new species based on the worker caste are described here. Morphological and bionomic information is presented for each species. A key to the species is given. Most of the species of this species group have more or less limited distribution ranges. This may be due to the poor dispersal ability generally seen among the Aenictus species, in which the propagule (reproductive unit) is an apterous queen plus accompanying workers (Jaitrong & Yamane 2013).

Materials and Methods

The specimens were collected using hand picking method. The taxonomic analysis was done using a Labomed stereo zoom microscope. Optika Litevision stereozoom microscope was used to take images and measurements. Images taken were subsequently cleaned as per the requirement for Adobe Photoshop CC 2017. Images of whole ants and micro sculpture of parts were obtained using ZESS scanning electron microscope. Measurements and indices follow Jaitrong & Yamane (2013). Taxonomy follow Bolton (1994), Jaitrong & Yamane (2011, 2013) and Bharti et al. (2012). Holotype is deposited at the Zoological Survey of India Western Ghats Regional Centre (ZSIWGRC), Kozhikode, Kerala, India.

Morphological terminology for measurements (given in millimeters) and indices include: HL—Maximum length of head in dorsal view, measured in straight line from the anterior most point of the median clypeal margin to the midpoint of a line drawn across the posterior margin of head; HW—Maximum width of head in dorsal view; SL—Maximum length of the scape excluding the basal neck and condyle; ML—Mesosoma length. In side view, maximum longitudinal distance from posteroventral corner of mesosoma to the farthest point on the anterior face of pronotum, excluding the neck; PTL—Maximum length of the petiole in dorsal view; PTH—Petiole Height. Maximum height of petiole in profile; PPTL—Maximum length of the postpetiole in dorsal view.

TL—Total Length. HL + ML + PTL + PPTL + GL.

CI—Cephalic Index. (HW/HL) × 100.

SI—Scape Index. (SL/HW) × 100.

Results

Diagnosis: Jaitrong & Yamane (2011) defined this species group as follows:

Antenna 10-segmented; scape reaching or extending beyond half of head length, but not reaching the occipital corner of head in full-face view. Mandible linear; it’s basal and lateral margins almost parallel; masticatory margin with large apical tooth followed by medium-sized subapical tooth; between subapical tooth and basal tooth 0–6 small denticles present. With mandibles closed, a gap is present between mandibles and anterior margin of clypeus. Anterior clypeal margin weakly concave or almost straight, lacking denticles. Frontal carina short and thin, reaching or slightly extending beyond the level of posterior margin of torulus; anterior curved extension of frontal carina reaching or extend-ing beyond the level of anterior clypeal margin in full-face view; parafrontal ridge absent. Promesonotum usually convex dorsally and sloping gradually to propodeum. Subpetiolar process developed. Head and first gastral tergite smooth and shiny. Body yellowish, reddish or dark brown; typhlatta spot absent.

Aenictus malakkaparensis sp. nov.

(Images 1–8)

urn:lsid:zoobank.org:act:7344C361-9591-470B-B359-479C1A68D2DC

Type material: Holotype: ZSI/WGRC/IR-INV.13903, 04.xii.2018, Female, worker, Malakkapara, Thrissur, India, Kerala, 10.280N, 76.861E, 1,016m, hand collection from ground, coll. A. Antony.

Holotype worker measurements: TL 2.57mm; HL 0.57mm; HW 0.49mm; SL 0.38mm; ML 0.90mm, PTL 0.21mm, PTH 0.19-mm, PPTL 0.20mm, CI 84; SI 77.

Worker description

Head: Head in full-face view sub rectangular, slightly longer than broad, sides convex, posterior margin almost straight; anterior part of head is broader than posterior part. Antennae with 10 segments, with ill-defined three segmented club and scape is short reaching almost 1/2 of head length. Anterior clypeal margin almost straight or feebly concave. Mandibles with basal margin edentate, masticatory margin of mandible with large acute apical tooth followed by a medium-sized subapical tooth, three denticles, and a medium-sized basal tooth.

Mesosome: Promesonotum convex dorsally and sloping gradually to metanotal groove; mesopleuron relatively long, clearly demarcated from metapleuron by a groove. Propodeum in profile with almost straight dorsal outline; propodeal junction angulate; declivity of propodeum flat, with blunt lateral carinae but not demarcated basally by a transverse carina.

Petiole, Post Petiole. Petiole longer than high, node short, elevated posteriorly and dorsal outline convex; sub petiolar process low and short, with anterior and posterior corners bluntly angulated and its ventral outline convex. Postpetiole clearly smaller than petiole, its dorsal outline convex.

Head, antenna and gaster entirely smooth and shiny; mandible finely striate with long decumbent hairs. Promesonotum smooth and shiny except for anteriormost portion punctate; mesopleuron with slightly irregular rugae; metapleuron, and propodeum wrinkled and reticulate. Petiole and postpetiole entirely reticulate except small area on dorsa smooth and shiny. Head and mesosoma dorsally with relatively sparse standing hairs. Legs with dense long decumbent hairs.

Mesosoma, petiole and postpetiole reddish-brown; head, antennal scape, gaster and legs yellowish-brown.

Etymology: The species name is after the type locality, Malakkapara.

Distribution: Known only from the type locality in Kerala.

Remarks: Aenictus malakkaparensis sp. nov. is similar to Aenictus appressipilosus from which it can be fairly separated by a combination of characters. Aenictus appressipilosus have two long standing hairs mixed with few short appressed hairs on the vertex and has a few appressed hairs mixed with few decumbent hairs on promesonotum whereas in Aenictus malakkaparensis sp. nov. two long standing hairs are absent and its sub petiolar process is low and short, with anterior and posterior corners bluntly angulated and the ventral outline convex.

Aenictus kodungallurensis sp. nov.

(Images 9–16)

urn:lsid:zoobank.org:act:353B7C3C-1BFD-42D6-8601-216C111509B3

Type material: Holotype: ZSI/WGRC/IR-INV.13902, 11.vi.2016, Female, worker, Kodungallur, Thrissur, Kerala, India, 10.238N, 76.161E, 9 m, hand collection on ground, coll. A. Antony.

Holotype worker measurements: TL 2.40mm; HL 0.54mm; HW 0.50mm; SL 0.40mm; ML 0.89mm, PTL 0.20mm, PTH 0.17mm, PPTL 0.17mm, CI 89; SI 76.

Worker description

Head: Head in full-face view sub rectangular, slightly longer than broad, sides convex, posterior margin almost straight; anterior part of head is broader than posterior part. Antennae with 10 segments, with ill-defined three segmented club and scape reaching almost 2/3 of head length. Anterior clypeal margin almost straight or feebly concave. Mandibles with basal margin edentate, masticatory margin of mandible with a large acute apical tooth followed by a medium-sized subapical tooth, two denticles, and a medium-sized basal tooth.

Petiole longer than high, node short, elevated posteriorly and dorsal outline convex; subpetiolar process low and subrectangular with anteroventral and posteroventral corners bluntly angulated and margin between the corners straight to feebly concave. Postpetiole clearly smaller than petiole, its dorsal outline convex.

Head, antenna and gaster entirely smooth and shiny; mandible finely striate. Promesonotum smooth and shiny except for anterior most portion punctate; mesopleuron with slightly irregular rugae; metapleuron, and propodeum wrinkled and reticulate. Petiole and postpetiole entirely reticulate except small area on dorsa smooth and shiny. Head and mesosoma dorsally with relatively dense standing hairs mixed with relatively dense decumbent hairs. Legs with dense long decumbent hairs. Mesosoma, petiole and postpetiole reddish-brown; head, antennal scape, gaster and legs yellowish-brown.

Etymology: The species name is after the type locality, Kodungallur.

Distribution: Known only from the type locality in Kerala.

Bionomics: So far, this species has been known only from Kodungallur.

Remarks: Aenictus kodungallurensis sp. nov. is collected from coastal area with loose coastal alluvium soil by handpicking method. Aeniictus kodungallurensis sp. nov. is smaller in size than Aenictus malakkaparensis sp nov. The antennal scape of Aenictus malakkaparensis sp nov. is shorter compared to Aenictus kodungallurensis sp. nov. The shape of subpetiolar process is also different, the ventral margine between corners is straight or feebly concave in Aenictus kodungallurensis sp. nov. but it is convex in Aenictus malakkaparensis sp. nov. Head and mesosome of Aenictus kodungallurensis sp. nov. is covered with dense hairs but in case of Aenictus malakkaparensis sp. nov. head and mesosome is only covered by sparse hairs.

Discussion

Aenictus kodungallurensis sp. nov. and Aenictus malakkaparensis sp. nov. are members of A. ceylonicus group, which is a unique group easily separated from the other groups by the following characteristics: mandible linear; a gap is present between mandibles and anterior margin of clypeus when mandibles are closed; anterior clypeal margin almost straight or feebly concave, lacking denticles. The A. ceylonicus group occurs in the Oriental, Indo-Australian and Australasian regions (Wilson 1964; Shattuck 2008; Jaitrong & Yamane 2011). A. kodungallurensis sp. nov. and A. malakkaparensis sp. nov. are the only members of Aenictus ceylonicus group reported from Kerala. Both the species are collected from ground by hand picking method. Major difference between both the species is in the structure of sub petiolar process and the promesonotum of A. kodungallurensis is covered with dense decumbent hairs. A. kodungallurensis sp. nov. is collected from a mixed vegetation area in coastal region with coastal alluvium soil whereas Aenictus malakkaparensis sp. nov. is collected from a hilly area with silty loam at an elevation of 1,016 m.

Key to A. ceylonicus group species based on the worker caste, modified and updated after the key of Jaitrong & Yamane (2013).

Mandible with 2–6 teeth/denticles between subapical and basal teeth (mandible with more than 4 teeth/denticles) .................. 2

- Mandible with 0–1 tooth/denticle between subapical and basal teeth (mandible with 3–4 teeth/denticles) .................... Extralimitial

Vertex with sparse standing hairs and with a few short appressed hairs; promesonotum with few appressed hairs and a few decumbent hairs ….….….….….….….….….….….….….….….….….….….….….….….......…... 3

- Vertex and promesonotum with dense standing or decumbent hairs ....….….….….….….….….….….….….….….….….….….….….…............ 4

Vertex with two long standing hairs mixed with a few short appressed hairs (Sabah) .... A. appressipilosus Jaitrong & Yamane, 2013

- Vertex without two long standing hairs but with a few short appressed hairs (India) ............................ A. malakkaparensis sp. nov.

Subpetiolar process subtriangular, its apex directed downward, anteroventrally not angulate; postpetiole elevated posteriorly; its posterior face much steeper than anterior face (Sumatra) ............................................................. A. itoi Jaitrong & Yamane, 2013

- Subpetiolar process subrectangular or low, convex, straight or feebly concave in its ventral outline, anteroventrally always angulate; postpetiole with roundly convex dorsal outline ..................................... ....................................................... 5

Dorsal outline of propodeum weakly convex; metapleural gland bulla weakly sculptured and shiny (Vietnam) ............................................................................................................ A. eguchii Jaitrong & Yamane, 2013

- Dorsal outline of propodeum straight; metapleural gland bulla strongly sculptured (puncto-reticulate) and opaque ……..…………. 6

Posteroventral corner of subpetiolar process bluntly angulate (not spiniform) (India) ......................... A. kodungallurensis sp. nov.

- Posteroventral corner of subpetiolar process acutely produced below (spiniform) ............. A. jawadwipa Jaitrong & Yamane, 2013

For images - - click here

References

Bharti, H., A.A. Wachoo & R. Kumar (2012). Two remarkable new species of Aenictus (Hymenoptera: Formicidae) from India. Journal of Asia-Pacific Entomology 15: 291–294. https://doi.org/10.1016/j.aspen.2012.02.002

Brady, S.G., B.L. Fisher, T.R. Schultz & P.S. Ward (2014). The rise of army ants and their relatives: diversification of specialized predatory doryline ants. BMC Evolutionary Biology 14: 93. http://www.biomedcentral.com/1471-2148/14/93

Bolton, B. (1994). Identification Guide to Ant Genera of The World. Mass.: Harvard University Press, Cambridge, 222 pp.

Bolton, B. (2020). An online catalogue of the ants of the world. http://www.antweb.org. Accessed on 3 July 2020.

Gotwald, W.H. (1995). Army Ants: The Biology of Social Predation. Cornell University Press, Ithaca and London, 320 pp.

Jaitrong, W. & S. Yamane (2011). Synopsis of Aenictus species groups and revision of the A. currax and A. laeviceps groups in the eastern Oriental, Indo-Australian, and Australasian regions (Hymenoptera: Formicidae: Aenictinae). Zootaxa 3128: 1–46. https://doi.org/10.11646/zootaxa.3128.1.1

Jaitrong, W. & S. Yamane (2013). The Aenictus ceylonicus species group (Hymenoptera, Formicidae, Aenictinae) from Southeast. Journal of Hymenoptera Research 31: 165–233. https://doi.org/10.3897/JHR.31.4274

Shattuck, S.O. (1999). Australian ants: their biology and identification. Monographs in Invertebrate Taxonomy 3: 1–226.

Shattuck, S.O. (2008). Review of the ant genus Aenictus (Hymenoptera: Formicidae) in Australia with notes on A. ceylonicus (Mayr). Zootaxa 1926: 1–19. https://doi.org/10.11646/zootaxa.1926.1.1

Wilson, E.O. (1964). The true army ants of the Indo-Australian area (Hymenoptera: Formicidae: Dorylinae). Pacific Insects 6(3): 427–483.