Pheidole praeusta Roger, 1863

Guerrero, Roberto J., García, Emira & Fernández, Fernando, 2022, The Pheidole Westwood, 1839 ants (Formicidae: Myrmicinae) in Colombia: new records including two species with remarkable morphology, Zootaxa 5154 (3), pp. 319-332 : 325-327

Pheidole praeusta Roger, 1863

( Figures 1–8 )

Pheidole praeusta Roger, 1863: 197 . Holotype soldier, "Island", Colombia [MHNG, AntWeb image of holotype examined, CASENT0915435]. Forel (1901): 361: minor worker described, Barranquilla, Colombia [NHMUK, AntWeb image of minor worker examined, CASENT0281753].

Pheidole amata Forel (1901) : 360. Lectotype soldier, Orihueca , Río Frio, Magdalena, Colombia [MHNG, AntWeb images examined, CASENT0908158]. New synonym.

Minor worker measurements (n=12): HW 0.47–0.61, HL 0.61–0.82, SL 0.80–1.00, EL 0.16–0.20, WL 0.80–1.04, PTW 0.10–0.12, PPW 0.16–0.20, CI 71–91, SI 163–175, PPI 150–200.

Soldier measurements (n= 7): HW 1.51–1.55, HL 1.86–1.90, SL 0.78–0.80, EL 0.27, WL 1.43–1.47, PSL 0.10, PTW 0.24–0.25, PPW 0.45–0.51, CI 81–82, SI 51–52, PSLI 5, PPI 192–200.

Super soldier measurements (n= 8): HW 2.17–2.46, HL 2.52–2.90, SL 0.87–1.10, EL 0.29–0.31, WL 1.22– 1.88, PSL 0.12–0.17, PTW 0.29–0.35, PPW 0.46–0.65, CI 85–88, SI 40–47, PSLI 4–7, PPI 160–191.

Description. Minor worker: In full-face view, oval-shaped head, with a smooth and shiny surface, with a developed occiput and occipital cavity; antennal fossa covered with punctuation and longitudinal carinulae. Very long antennal escape. In lateral view, pronotum smooth and shiny, mesopleura and propodeum covered with punctuation fine and very indistinct, the latter with propodeal spines reduced to a pair of denticles. Petiole and postpetiole with inconspicuous punctuation. Dorsum of first gastral tergite smooth and shiny. Long yellowish hairs covering the entire surface of the body. Soldier: In full face view, anterior half of the head with parallel longitudinal costulae; posterior part of antennal fossa covered with rugoreticulae. Striae surrounding the eyes longer than those formed between the frontal carinae, forming a “w”-shaped pattern, the entire costulae covered by fine and indistinct punctuation. Smooth and shiny occipital lobes. hypostomal margin straight, with a large, blunt, gibbous middle tooth, prominent outer hypostomal teeth, broad towards the base and pointed towards the apex, separated from each other; inner hypostomal teeth pointed, protruding behind the outer ones. In lateral view, pronotum striated transversely, with indistinct punctuation, and a smooth, shiny patch in the middle; mesopleura with conspicuous punctuation; propodeum provided with developed propodeal spines, dorsal surface covered with conspicuous punctuation and some longitudinal striae. In dorsal view, pronotum covered with short transverse carinulae, with a smooth and shiny medium patch. Anterior portion of the first gastral tergite covered with very short carinulae that extend from the helcium, the rest of the tergum is smooth and shiny, covered with conspicuous foveae, and abundant yellowish, long and suberect hairs emerge. Super soldier. In dorsal view, clypeus as in the soldier. Dorsal surface of the head covered by costulae arranged in a “w” pattern, although unlike the soldier, those costulae originating between the frontal carinae are longer, reaching and sometimes exceeding the length of the costulae close to the eyes, occipital lobes smooth and shiny. Hypostomal margin concave, with prominent middle tooth, thick and gibbous, inner hypostomal teeth broad towards the base and pointed towards the apex, prominent and triangular outer hypostomal teeth. In lateral view, mesosome covered with conspicuous transverse striae; pronotum with small medium patch smooth and shiny; propodeum provided with slender propodeal spines. In dorsal view, mid-posterior portion of the pronotum smooth and shiny, the rest covered by transverse striae; Propodeum covered with transverse striae and conspicuous punctuation. Anterior portion of the first tergite of the gaster covered with short longitudinal carinulae extending from the helcium. Head and mesosome covered with erect and suberect yellowish hairs. Petiole, postpetiole and gaster with yellow and decumbent hairs.

Material examined. Colombia: 1 soldier, Magdalena, Aracataca, Vereda Macaraquilla, Finca San José Sur , Oil palm plantation, 10.5721, -74.1933, alt. 41m, 22. Oct. 2017. Coll. T. Franco & J M Ramírez, pitfall [CBUM]; 5 minor workers, 4 soldier, 5 super soldiers, Aracataca, Vereda Macaraquilla, Finca Macaraquilla , Oil palm plantation, 10.5759, -74.1764, alt. 51m, 22. Oct. 2017. Coll. T. Franco & J M Ramírez, pitfall [CBUM]; 2 minor workers, Aracataca, Vereda Macaraquilla, Finca San José Sur, Oil palm plantation, 10.5721, -74.1922, alt. 40m, 21. Oct. 2017. Coll. T. Franco & J M Ramírez, pitfall [CBUM]; 1 super soldier, Aracataca, Vereda Macaraquilla, Finca San José Sur, Oil palm plantation, 10.5725, -74.1864, alt. 41m, 17. Sep. 2017. Coll. T. Franco & J M Ramírez, pitfall [CBUM]. 10 minor workers, 3 soldiers, 3 super soldiers, Santa Marta, Parcela Bosque Seco Universidad del Magdalena, 11.2167, y -74.1833, alt. 21 m, 13. Oct. 2021. Coll. R.J. Guerrero, dug nest [CBUM].

Comments. This species is known from Colombia, Ecuador, and Brazil. Pheidole praeusta is recorded here as the first currently known trimorphic worker subcaste species for South America, possessing an unusually large super soldier subcaste in addition to the typical minor worker and soldier subcastes.

Pheidole praeusta was described from a single soldier by Roger (1863), which prevented him from commenting on the remarkable morphology of this species. Later, Forel (1901) observed the nest structure of P. praeusta in different sites in the Colombian Caribbean region and commented on the exaggerated differences in head size between workers and “soldiers”. Despite the excavation of nests of P. praeusta, Forel (1901) does not comment on the dimorphism among the soldier subcaste that we recorded here.

Specimens collected from pitfalls in Aracataca ( Magdalena, Colombia) allowed us to identify within the series several ants with a soldier-like morphology different in the size of the head and mesosoma from those described in P. preusta . Since P. praeusta was previously recorded in the dry forest reserve of the Universidad del Magdalena in Santa Marta ( Ramos et al. 2022), RJG installed protein baits at various points within the reserve, attracting workers and a soldier of P. praeusta . Those ants were followed to the nest, which was partially excavated, extracting 10 minor workers, three soldier-like workers, and three super soldier workers. The ants collected in Aracataca and Santa Marta show that P. preusta colonies are composed of minor workers, soldiers, and super soldiers morphometrically different from each other (i.e., the soldiers are dimorphic); soldiers have a shorter mesosoma than super soldiers ( Fig. 7 ), and there is a strong gap in head size between the two subcastes ( Fig. 8 ). It is observed that the variance in the size of the head is lower for the soldiers than for the supersoldiers, but in this last subcaste with a growth of the head. The lower variance in the dimorphic soldiers of P. praeusta apparently contrasts with that shown in another trimorphic species, Pheidole rhea Wheeler, W.M., 1908 , in which the soldiers show greater variability than the super soldiers ( Huang & Wheeler 2011). The data on Pheidole praeusta are just an approximation to the contrasting pattern shown by other trimorphic species, however the exploration of more nests covering the distribution of this species would allow for more information to analyze possible allometric patterns.

The minor workers and soldiers of P. praeusta are very similar to these subcastes of P. amata Forel 1901 , based on morphometrics (using Longino 2009b) and examining images. The morphometric traits HL, HW, SL, and WL of the P. praeusta minor worker and soldier completely matched those measurements recorded for P. amata Likewise , the morphological features shape of anteroclypeal margin, occipital cleft deep, carinule pattern on head, and erect pilosity on body match among the soldiers of both taxa. Wilson (2003) suggests several differences between minor workers of P. praeusta and P. amata (e.g., propodeal spine reduced to denticle vs propodeal spine absent, respectively) but we find no morphological evidence to separate them, as suggested by Forel (1901). Given the morphological similarity of the worker and soldier subcastes as well as the proximity of the type localities, they are almost certainly the same species, and we synonymize P. amata under P. praeusta .

Figures

FIGURES 1–6. Pheidole praeusta Roger. 1) Head in full-face view of the super soldier subcaste. 2) Head in full-face view of the soldier subcaste. 3) Head in full-face view of the worker subcaste. 4) Body in lateral view of the super soldier subcaste. 5) Body in lateral view of the soldier subcaste. 6) Body in lateral view of the worker subcaste. Scale bar= 0.5 mm. Super soldier (CBUMAG:ENT13467), soldier (CBUMAG:ENT13071), and minor worker (CBUMAG:ENT13463) photos by R.J. Guerrero.

FIGURES 7–8. Bivariate plots of measurements of Pheidole praeusta Roger. 7. Relationship between WL and HL. 8. Relationship between HL and HW. The red solid line green solid line, and blue solid line correspond to the minor worker, soldier, and super soldier subcastes measurements, respectively.