Strumigenys subtilis, Booher, 2021

Booher, Douglas B., 2021, The ant genus Strumigenys Smith, 1860 (Hymenoptera: Formicidae) in western North America North of Mexico, Zootaxa 5061 (2), pp. 201-248 : 242-244

Strumigenys subtilis sp. nov.

Figure 42

Distribution. USA; California.

Type material examined. Holotype Queen. USA, California, San Bernardino County, 1 mile west of Pichalka Spring, Clark Mountains , blackbush scrub, pitfall trap, 35.5185 -115.64213, 4 January 2006, 4600 ft, Collector J. des Lauriers, unique specimen identifier (casent0104307) [ PSWC].

Holotype queen measurements: HL = 0.685; HW = 0.422; ML = 0.105; PW = 0.304; SL = 0.390; FL = 0.513; HT = 0.359; EL = 0.122; WL = 0.716; CI = 61.6; SI = 92.4; MI = 15.3.

Diagnosis. Strumigenys subtilis is the only western species possessing a narrow peripheral groove along the free margin of the clypeus and highly reduced spongiform appendages. All eastern USA species with a peripheral groove also have well developed lateral petiolar and post-petiolar spongiform appendages; these spongiform appendages are reduced to narrow cuticular lamellae in S. subtilis . Strumigenys subtilis superficially resembles S. inopina ( Deyrup & Cover, 1998) , a southeastern USA species only known from a few queens and suspected to be a social parasite, but is easily distinguished by the presence of short basigastral costulae in S. subtilis (in S. inopina costulae are absent) ( Bolton 2000).

Description of worker. Mandibles with a triangular basal lamella with basal free side at least three times longer than anterior facing free side. Mandibles with six principle teeth, first three basal teeth are largest and about equal in length followed by three smaller teeth with tooth five being the longest and tooth six being the shortest. Principle teeth followed by five similarly sized blunt denticles and terminating with an elongated and acute apical tooth for a total tooth count of 12. Labrum with apical digitate lobes that curve ventrally. Clypeus with narrow peripheral groove; anterior border of ventral lamella of groove projecting further than dorsal lamella in full frontal view. Anterior border of clypeus broadly rounded between mandible insertions; lateral free margin weakly concave between lateral posterior corners to mandible insertion; 1.22 times broader than long. In profile posterior border of clypeus is abruptly raised above adjoining frontal area. Free margin of ocular carina is irregular in full frontal view. Head having expanded posterior-lateral corners located below midpoint of head in lateral view. Anterior and lateral dorsum of pronotum marginate. Pronotum slightly smaller in width (0.304) than mesosoma (0.390). Propodeal spines triangular and lamellate; about equal in length to maximum width of broadly convex free margin of declivitous lamella.

Pilosity. Setae on anterior margin of scape shallowly curved simple and acutely tipped with one or two setae curving towards the base of scape. Differentiated elongate flagellate to subflagellate setae present at apicoscrobal position; two pairs present between occipital posterior corners and midline of head just anterior of posterior margin; ventral surface of head with three pairs positioned at posterior ventral occipital margin, below position of eyes, and at rear of postbuccal groove; four pairs present on dorsum mesonotum; two pairs present on lateral dorsal surfaces of petiole and postpetiole; one pair of standing setae on anterior third of first gastral tergite that straddle the midline; two pairs of elongate simple setae present on mesa- and metatibia and one or two present on mesa- and meta-basitarsi. Ground pilosity of head, mesosoma, and gaster numerous fine, apically acute, and shallowly curved elongate setae. Ground pilosity on dorsum and borders of clypeus directed towards mandibles; on dorsum of head these setae are directed anteriorly or medially; on dorsum of mesosoma these setae directed medially to posteriorly. Ground pilosity of first gastral tergite elongate irregularly curved to flagellate setae closely following the surface of gaster.

Sculpture. Dorsum of clypeus smooth with light punctations along lateral and posterior borders. Frontal area with large smooth oval patch free of sculpture. Dorsum of head reticulopunctate and heaviest in posterior portion near the posterior margin of head. Dorsum of pronotum smooth and shining. Dorsum of mesosoma punctate. Side of pronotum mostly smooth and shining with finely punctate sculpture heaviest peripherally. Pleurae and side of propodeum smooth with some peripheral punctate sculpture. Dorsal surfaces of petiolar and postpetiolar node smooth and shining. Gaster smooth and shining with extremely short basigastral costulae (maximum length 0.016).

Spongiform appendages. Dorsal and lateral spongiform appendages of petiole and postpetiole are reduce to weakly sculptured cuticular ridges or lamellae. Ventral lamella of petiole at most ¼ of the depth of the peduncle of petiole; translucent and weakly reticulopunctate along lowest portion; ending anteriorly as a well-defined short sharp tooth. Sub-postpetiolar process lamellate; weakly reticulopunctate and shorter (0.92) than exposed height of postpetiolar node.

Etymology. Named for the subtle sculpturing and fine pilosity of this species. The specific epithet subtilis (meaning “fine”) is a Latin singular feminine adjective in the nominative case and refers to the subtle sculpturing and fine pilosity of this species.

Comments. Strumigenys subtilis is known from a single specimen collected during a survey of the ant fauna of the Mohave National Preserve. Strumigenys subtilis is likely an inquiline or social parasite as it shares several common characters with other presumed or known Strumigenys inquilines: S. inopina ( Deyrup & Cover, 1998) , S. inquilina ( Bolton, 1983) , and S. subnuda ( MacGown & Hill, 2010) . Shared characters include reduced sculpture, small or absent spongiform appendages, and simple non-expanded setae ( MacGown & Hill 2010; Deyrup & Cover 1998). However, it is not likely these expected inquiline species are closely related. The unusual and uncommon character of the peripheral groove and similar dentition as species in the clypeata group suggest S. subtilis is potentially a member of this group. However, no other members of the clypeata group have ranges that extend much further west than eastern Texas, and several other morphological differences, e.g. short basal gastral costulae, are not consistent with the clypeata group ( Bolton 2000).

Figures

FIGURE 42. Holotype queen of Strumigenys subtilis [PSWC: casent0104307]. Photographed by Michele Esposito (AntWeb 2021).