Temnothorax arbustus

Known only from the type collection, taken from a nest in a small hollow branch of Bursera.

Identification
Prebus (2021) - Temnothorax arbustus can be separated from other species in the salvini clade by the following character combination: head relatively broad (CI 87-88); erect setae present on gula; metanotal groove absent; propodeum not depressed; propodeum bearing erect setae; propodeal spines short, slightly shorter than the propodeal declivity (PSI 26-28); hind femora strongly incrassate (FI 379-427); petiole with short peduncle: peduncle comprising about a quarter of the total length of the petiole; petiolar node erect and subquadrate, not overhanging the caudal cylinder in profile view; posterior margin of petiolar node distinct in profile view, about two thirds as long as dorsal margin; postpetiole narrow (PWI 154-163); first gastral tergite smooth and shining; integument dark brown; dorsum of head, mesosoma, waist segments and gaster with erect, short, blunt-tipped setae; legs without erect setae.

Similar species: Temnothorax caguatan, Temnothorax obturator, Temnothorax politus, Temnothorax rugosus, Temnothorax subditivus, Temnothorax tenuisculptus, Temnothorax whitfordi, and other members of the annexus group. Temnothorax arbustus can be separated from all of the above species, except for T. rugosus and other members of the annexus group, by the medially emarginate anterior clypeal margin. Furthermore, it can be distinguished from T. caguatan and T. whitfordi by the 12-segmented antennae, which are 11-segmented in the latter two. Additionally, the absence of long, tapering setae on the legs and most other surfaces of the body will differentiate T. arbustus from T. politus. The erect, subquadrate petiolar node of T. arbustus contrasts with the node of T. subditivus, which is squamiform, and the node of T. rugosus, which is cuneiform to subcuneiform. The dorsal margin of the mesosoma is continuous in T. arbustus (as opposed to sinuate with a depressed propodeum in T. tenuisculptus). Within the annexus group, the following characters distinguish T. arbustus from its close relatives: gular region with erect setae, as opposed to absent (Temnothorax quercicola) or present but decumbent (Temnothorax annexus); head relatively broad (CI 87-88 vs. 80-84 in Temnothorax balnearius); a petiole with a distinct posterior face in lateral view, which is about two thirds as long as the dorsal face will separate T. arbustus from Temnothorax obtusigaster, which has a very short posterior face of the petiole; the first gastral tergite of T. arbustus is not sculptured, as opposed to T. obtusigaster, which has an areolate first gastral tergite.

Temnothorax arbustus was mistakenly reported as T. sp. nr. peninsularis in Prebus (2017). Temnothorax peninsularis is a member of the distantly related sallei clade, which is morphologically convergent with members of the salvini clade (Prebus, in prep.). Temnothorax peninsularis was described from a dealate gyne but differs from other gynes in the annexus group by the absence a medial depression or notch in the anterior margin of the clypeus (Mackay, 2000; Wheeler, 1934, see CASENT0922107 on antweb.org).

Distribution
The only known specimens are from the type collection, which were found in a low elevation site in Baja California Sur.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Biology
Prebus (2021) - Known only from the type specimens, which were extracted from a nest in a small hollow branch of Bursera in the subtropical dry forests of Baja California Sur by Bob Johnson. Like other members of the annexus group, this species most likely nests exclusively in dead plant material on live plants.

Nomenclature

 * . Temnothorax arbustus Prebus, 2021: 98, figs. 95B, 97 (w.) MEXICO (Baja California Sur).

Worker
(n = 2): SL = 0.683-0.701 (0.692); FRS = 0.306-0.310 (0.308); CW = 0.928-0.969 (0.949); CWb = 0.848-0.895 (0.872); PoOC = 0.394-0.407 (0.401); CL = 0.962-1.028 (0.995); EL = 0.240-0.263 (0.252); EW = 0.196-0.212 (0.204); MD = 0.225-0.227 (0.226); WL = 1.357-1.445 (1.401); SPST = 0.376-0.380 (0.378); MPST = 0.416-0.439 (0.428); PEL = 0.455-0.477 (0.466); NOL = 0.271-0.279 (0.275); NOH = 0.196-0.209 (0.203); PEH = 0.351-0.376 (0.364); PPL = 0.294-0.335 (0.315); PW = 0.622-0.648 (0.635); SBPA = 0.284-0.300 (0.292); SPTI = 0.334-0.353 (0.344); PEW = 0.238-0.242 (0.240); PNW = 0.198-0.210 (0.204); PPW = 0.373-0.388 (0.381); HFL = 0.798-0.839 (0.819); HFWmax = 0.265-0.269 (0.267); HFWmin = 0.062-0.071 (0.067); CS = 1.329-1.409 (1.369); ES = 0.338-0.369 (0.354); SI = 78-81 (79); OI = 25-26 (26); CI = 87-88 (88); WLI = 160-161 (161); SBI = 33-34 (34); PSI = 26-28 (27); PWI = 154-163 (159); PLI = 136-162 (149); NI = 130-142 (136); PNWI = 83-87 (85); NLI = 58-60 (59); FI = 379-427 (403).

In full-face view, head subquadrate, slightly longer than broad (CI 87-88). Mandibles densely, finely striate but shining and armed with five teeth: the apical-most well developed and acute, followed by a less developed preapical tooth and three equally developed smaller teeth. Anterior clypeal margin emarginated medially. Antennal scapes short: when fully retracted, failing to reach the posterior margin of the head capsule by about the maximum width of the antennal scape (SI 78-81). Antennae 12-segmented; antennal club of composed of three segments, with the apical-most segment about one and a half times as long as the preceding two in combination. Frontal carinae moderately long, extending past the antennal toruli by about two times the maximum width of the antennal scape. Compound eyes strongly protruding past the lateral margins of the head capsule. Lateral margin of head weakly convex, forming a continuous arc from the mandibular insertions to the posterior margin of the head. Posterior head margin weakly concave medially but rounding evenly into the lateral margins.

In profile view, compound eyes ovular and moderately large (OI 25-26), with 15 ommatidia in longest row. Pronotal declivity distinct: dorsal margin of anterior face of pronotum marked by a very weak carina; neck and anterior face of pronotum forming a ~120° angle. Mesosoma very weakly sinuate: weakly convex from where it joins the pronotal declivity to the propodeum, the propodeum slightly depressed and weakly concave. Promesonotal suture extending from the posterior margin of the procoxal insertion to the mesothoracic spiracle, which is moderately well developed. Metanotal groove visible as a disruption of the sculpture laterally from where it arises between the mid- and hind coxae to where it ends in the poorly developed metathoracic spiracle, which is nearly indistinguishable against the ground sculpture. Propodeal spiracle moderately well developed, directed posterolaterally, and separated from the propodeal declivity by about five spiracle diameters. Propodeal spines moderately well developed, but short (PSI 26-28), slightly shorter than the propodeal declivity, slightly flared at the base, straight, and blunt. Propodeal declivity weakly concave, forming a rounded ~100° angle with the base of the propodeal spines. Propodeal lobes rounded and weakly developed, but with an angulate dorsal margin. Metapleural gland bulla small, extending from the metacoxal insertion a third of the way to the propodeal spiracle. Petiole short (PLI 136-162), with tubercles anterodorsally. Subpetiolar process in the form of a moderately long, acute, triangular tooth; ventral margin of petiole weakly concave posterior to it. Petiolar peduncle short: comprising about a quarter of the total petiole length. Petiolar node robust, erect, and subquadrate: transition between peduncle and node marked by a rounded angle of ~110°; anterior face forming a ~100° angle with the dorsal face, which is weakly convex, nearly flat; dorsal face meeting the posterior face at a rounded ~90° angle; posterior face forms a ~110° angle with the caudal cylinder. Postpetiole flat anteriorly, bulging slightly anterodorsally before flattening posterodorsally; weakly lobed ventrally.

In dorsal view, humeri weakly developed: evenly rounded and slightly wider than the rest of the mesosoma; mesothoracic spiracles weakly protruding past the lateral margins of the mesosoma, visible as slight angles where the pronotum meets the mesonotum. Promesonotal suture represented weak sulcus and disruption in the ground sculpture. Metanotal groove represented by a weak sulcus. Propodeal spines broadly approximated basally and weakly diverging apically, their apices separated from each other by slightly more than their length, the negative space between them â€ € shaped. Petiolar peduncle with spiracles weakly protruding past the lateral margins. Petiolar node nearly ovular, but posterior margin flattened; node the same width as the peduncle, and evenly grading into the caudal cylinder, which is slightly wider than the node. Postpetiole narrow (PWI 154-163) and subquadrate. Anterior margin of the postpetiole very weakly convex, nearly flat, and meet the lateral margins at a ~90° angle; lateral margins converge parallel to each other; posterior corners rounded; posterior margin flat. Metafemur strongly incrassate (FI 379-427).

Sculpture: median clypeal carina present, extending posteriorly to the frontal triangle, and flanked on either side by two slightly weaker carinae. Lateral clypeal lobes with additional, weaker carinae; ground sculpture weakly areolate. Antennal scapes areolate. Cephalic dorsum weakly areolate, with coarse rugae over the ground sculpture; concentric costulae surrounding the antennal insertions; sculpture between the frontal carinae costate. Lateral surfaces of head areolate, with coarse rugae over the ground sculpture. Ventral surface of head smooth and shining anteromedially, but otherwise weakly areolatecostulate. Pronotal neck areolate. Lateral surfaces mesosoma areolate, with costae over the ground sculpture; region between propodeal spiracle and base of propodeal spines areolate. Propodeal declivity areolate. Dorsal surface of mesosoma predominantly areolate, with rugulae that become very weak on the mesonotum. Femora finely, densely areolate. Petiole uniformly areolate; a weak carina present laterally, extending longitudinally from the petiolar spiracle to the caudal cylinder; areolate-rugulose on the dorsal and posterior faces of the node. Postpetiole uniformly areolate, with rugulose sculpture on the lateral faces. First gastral tergite and sternite smooth and shining, without spectral iridescence.

Setae: antennal scapes and funiculi with short, adpressed pilosity. Dorsum of the head, pronotum, waist segments, and gaster with moderately abundant, erect, blunt-tipped setae, the longest of which are about the width of the compound eye. The head bears ~38, mesosoma ~28, petiole 6, postpetiole ~18, and first gastral tergite ~90 setae. Short, sparse pubescence present over the entire body, but difficult to detect against the densely sculptured integument.

Color: predominantly dark brown, with antennae, mandibles, pronotal neck, legs (excluding femora), basal third of gastral sclerites (excluding the first gastral sclerites), and sting testaceous brown.

Type Material
Holotype worker: MEXICO: Baja California Sur: 14 km NE Hwy 19 turnoff to Presa Santa Inez, 23.590000° N 110.091667° W, 385 m, 21 March 2014, R.A. Johnson #5277, dry forest with Bursera, Jatropha, Quercus, Pachycereus, organpipe, 5 cm dead branch Bursera (CASENT0758357).

Paratype workers: MEXICO: Baja California Sur: same data as holotype, 1 worker (CASENT0733967) 2 workers (CASENT0869068)

Etymology
Behavioural, from the Spanish ʻarbusta' (= shrub), in reference to the dry forest and nesting site in which this species was collected.