A NEW SPECIES OF THE Odontomachus infandus SPECIES GROUP (HYMENOPTERA: FORMICIDAE) FROM PANGASINAN, PHILIPPINES, WITH NOTES ON SPECIES ECOLOGY

ARTICLE HIGLIGHTS
- New species of Odontomachus
- Distribution and ecological notes
- Updated species key

ABSTRACT
A new species of Odontomachus Latreille, 1804 named O. ampipitbaybay sp. nov. is illustrated and described from specimens collected along the coastal area of Alaminos City, Pangasinan, Luzon Island, Philippines, with notes on its species ecology. The new species is diagnosed and compared against closely related species from Luzon. A distribution map of selected Philippine Odontomachus species is provided, and a modification to the key to the Philippine Odontomachus is proposed.

INTRODUCTION

Philippine ants are of great interest due to their high richness brought by the geologic history and diverse ecological features of the archipelago. However, only about half of the estimated 1,000 species of Philippine ants have been discovered and described thus far, and much of their biology is still unknown(General & Alpert, 2012). Unfortunately, the inherent challenges brought by the country’s archipelagic setting and the few myrmecologists in the field coupled with low funding opportunities produce a poor picture of ant diversity and distribution in the Philippines(General, 2021). Being still understudied, the Philippine ant fauna offers many opportunities to researchers.

One notable group of ants, especially in rural areas, are the trap-jaw ants from the genus Odontomachus Latreille, 1804, locally termed ampipit by the Ilocano-speaking Pangasinenses. These are large ground-foraging ants that are easily recognized by their elongated mandibles, often seen wide open when threatened or ready to capture their prey. This genus comprises 74 valid extant species(AntWeb, 2024);(Bolton, 2024). General and(General & Alpert, 2012)listed 11 species in the Philippines. In(Sorger & Zettel, 2011)review of this genus, they provided a key for the Philippines that contains a different list of 11 species that includes 2 unnamed species. The most recent additions to the Philippine fauna are the new species, O. ferminae General, 2018, from Sibuyan Island(General, 2018)and O. pangantihoni(Zettel & Sorger, 2023)from Panay Island(Zettel & Sorger, 2023). At present, there is a total of 13 valid species in the Philippines.

In their review,(Sorger & Zettel, 2011)distinguished two sets within Odontomachus. The first set contains three unrelated species from three species groups, namely O. simillimus, O. malignus, and O. rixosus. The other set includes the infandus species group composed of regionally endemic and often forest-dwelling species.

Before this study, the infandus species group was represented in the Philippines by eight described species: Odontomachus alius(Sorger & Zettel, 2011), Odontomachus banksi Forel, 1910, Odontomachus ferminae General, 2018, Odontomachus infandus Smith, 1858, Odontomachus pangantihoni Zettel & Sorger, 2023, Odontomachus philippinus Emery, 1893, Odontomachus schoedli Sorger & Zettel, 2011, and Odontomachus scifictus(Sorger & Zettel, 2011)((Bolton, 2024);(AntWeb, 2024)).

After a brief collecting trip in a coastal forest fragment in Alaminos City in the Northwestern part of Pangasinan, Luzon Island (Figure 1), several specimens of trap-jaw ants that were superficially similar to the highland O. schoedli were collected. Further examination revealed that these specimens constitute a new species, herein described, belonging to the infandus species group. This discovery is a testament to the rich diversity of Philippine ants and terrestrial arthropods in general, eliciting more research in understudied habitats, especially in threatened areas.

MATERIALS AND METHODS

The specimens described herein were collected from a small undisturbed beach adjacent to Bolo Beach, on coastal limestone aggregates with a small forest fragment near the Hundred Islands National Park. Foraging worker specimens were manually collected and pinned on cardboard mounts. Specimens were examined, measured, and imaged using an Olympus SZ61 stereomicroscope with Touptek camera attachment (Model XCAMTOP4K8MPA) and ToupView software version X64. The morphology of O. infandus and O. schoedli followed Sorger & Zettel (2011) and additional data of types were acquired from AntWeb (2024). Measurements were given from holotype followed by paratype mean (paratype m; n = 7) and the paratype minimum (min) and maximum (max) values in parenthesis: holotype (paratype m, min–max). All measurements were given in millimeters rounded to the nearest 0.01 mm. Measurements and indices followed(Sorger & Zettel, 2011)and(General, 2018), including the additional index (PtI).

Measurements:

TLTotal length. Length of the entire ant measured in dorsal view with head stretched out, from anterior margin of the mandible to apex of gaster, excluding sting.

HLHead length. Maximum length of the head in full-face view, excluding mandibles, measured from anteriormost point of clypeal margin to posterior-most point of head vertex, parallel to midline.

HWHead width. Maximum width of head in full-face view (including eyes when surpassing head outline).

MdLMandible length. Maximum length of the mandible in frontal view of head measured from mandibular insertion to apex.

MsLMesosoma length. Maximum length of mesosoma, measured in lateral view, diagonal from cervical shield to the posterolateral propodeal edge.

PnWPronotum width. Maximum width of pronotum in dorsal view.

PtHPetiole height. Maximum height of petiole, measured in lateral view as a straight line from the bottom edge of the petiole, perpendicular to petiolar apex.

PtLPetiole length. Measured in lateral view along the dorsal outline of petiole from small antero-apical tooth to apex.

PtWPetiole width. Maximum width of petiole in dorsal view.

SLScape length. Maximum length of antennal scape in dorsal view excluding basal constriction.

GLGaster length, maximum length from base of first gastral tergite to the apex of gaster, excluding sting, measured in lateral view.

Indices:

CICephalic index. HW / HL × 100 MdI Mandible index. MdL / HL × 100 SI Scape index. SL / HW × 100

PtIPetiole index. PtH / PtL × 100

Depositories:

PASIPhilippine Arachnological Society, Inc. - Reference Collection, Manila

PNMPhilippine National Museum of Natural History, Manila

Figure 1.Distribution map of selected Odontomachus species showing records of O. ampipitbaybay sp. nov. (red), O. schoedli (green), and O. infandus (blue) based on this study and Sorger & Zettel

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