Novomessor albisetosus

Taxonomy

Novomessor albisetosus was first identified by Austrian entomologist Gustav Mayr in 1886, who provided the first description of the ant in his journal article Die Formiciden der Vereinigten Staaten von Nordamerika. In his journal, N. albisetosus was originally known as Aphaenogaster albisetosa. In 1895, Italian entomologist Carlo Emery classified Aphaenogaster as a subgenus of Stenamma, and N. albisetosus was renamed as Stenamma (Aphaenogaster) albisetosum. Emery would later transfer the species to the newly erected genus Novomessor, a genus he described in 1915 which included Novomessor cockerelli. In 1947, Jane Enzmann described a new species, Novomessor cockerelli minor. She distinguishes it from N. cockerelli by its smaller size, lighter color and more sculptured body shape. This taxon, however, was synonymized with N. albisetosus two years later.

Novomessor was synonymized in 1974, and so N. albisetosus was moved to Aphaenogaster. However, scientists revived the genus in 1976 and stated that N. albisetosus and N. cockerelli had an exocrine gastral glandular system that was not found in any examined Aphaenogaster ant. In 1982, English myrmecologist Barry Bolton argues that basing the genus on such feature cannot justify the separation of Novomessor and Aphaenogaster. In 2015, a phylogenetic study concluded that Novomessor was genetically distinct from Aphaenogaster, and the genus was revived from synonymy to reinstate N. albisetosus as one of the three known species.

Description

N. albisetosus is a medium-sized species with a moderately short body, measuring 6 to 8.5 millimetres (0.2 to 0.3 in). The body color of the ant is ferruginous, the legs are reddish brown and the petiole and abdomen are brownish black. The first segment of the abdomen, however, is brownish yellow. The tibia has fine and clear bristle. The maxillae both form a triangle-shaped isoscele, and the mandibles have three comparatively large teeth. The head is noticeably long, which is longer than its total width. The clypeus is also longer than wide and is found in the middle of the head which forms two vertical stripes.

Larvae of N. albisetosus measure 6.6 millimetres (0.3 in). The body is moderately stout and at the first and second abdominal somites, there is a slight constriction. Spiracles are small and no spinules are on the integument. Body hairs are short and sparse; hairs on the head are sparse and also short. The antennae are small and bear three sensilla and the labrum is short. The mandibles are sclerotized, and the apex forms a long slender tooth which is medially curved. The maxillae are small with a spinulose apex. Larvae appear similar to that of N. ensifer, but N. ensifer larvae can be distinguished by the abundance of hair with long stouts found on the body.

N. albisetosus can be distinguished from other members in Novomessor. One such feature is the head of N. albisetosus is shorter than that of N. cockerelli. The sides of the head in front of the eyes are also subparallel, but behind the eyes they become convex. N. albisetosus has spines that are more bent and curve downward, whereas the spines of N. cockerelli are bent inward. Both species share a similarly structured thoracic, but the epinotal spines in N. albisetosus are just as long as the basal face of the epinotum. Meanwhile, N. cockerelli has shorter epinotal spines. N. albisetosus has a heavier structure and also has a greater degree of opacity, in which its petiole is almost opaque. The ant is hairier than N. albisetosus, where the body is covered in coarse whitish-yellow hairs. The hairs taper from the base to the tip, but they appear blunt. The abdomen bears numerous hairs that are shorter than the hair found on the pronotum. The queens can be distinguished from each other by the cephalic structure, where the head of N. albisetosus is slightly longer than it is broad, whereas the heads of N. cockerelli are decidedly longer than broad. As well as that, the thorax of N. albisetosus is shorter and higher in contrast to N. cockerelli. Differences in their sculptures and pilosity is less noticeable, but N. cockerelli has a shinier epinotum and the head is rugose. Males of N. cockerelli are smaller (measuring 6 millimetres (0.2 in)) and have short heads, and the mesonotum is covered with weak rugose.

Distribution and habitat

N. albisetosus is native to Mexico and south-western United States, where it's geographical presence ranges from the U.S. states of Texas, New Mexico and Arizona. In Mexico, the ant is found in the state of Chihuahua, Durango and Sonora. The ant is less common than its relative N. cockerelli. The eastern distributional range of N. albisetosus is not exactly known, but it does not coincide with N. cockerelli. The eastern-most record of N. albisetosus extends towards the Cernas Ranch in the Chisos Mountains of Texas. The mountains are so close to northern Coahuila that the ant may be scarcely absent within the Mexican ranges. In contrast to N. cockerelli, N. albisetosus does not extend further north and much further south. Both ants are found on the eastern side of Sierra until the topography changes in northwestern Chihuahua. Up north, Sierra breaks up a number of ranges which communicate on the east of the Mexican Plateau, and to the west, with the narrow Sonoran coastal plain. The elevation of these valleys gradually descend by several thousand feet, where both N. albisetosus and N. cockerelli are widely present. However, N. albisetosus is less extensive than N. cockerelli. The northern limit is mostly determined by the inability to occupy highland areas in central Arizona and New Mexico, but in southeastern Wickenburg, Arizona, the range of N. albisetosus runs along the southern end of the area, in which the rise of the Mogollon Mesa begins; the elevation of Mogollon Mesa is too great for N. albisetosus to reach the top.