Notaferrum n. gen. (Coleoptera: Ptinidae): the first known spider beetle associated with weaver ants

ABSTRACT A new genus name Notaferrum n. gen. is proposed for Ptinus natalensis Pic, 1906. The taxon is diagnosed and described and the only known species redescribed. This taxon, well outside the concept of the genus Ptinus Linnaeus, 1766, is most distinctly characterized by a pair of longitudinal and vertically oriented blade-like ridges located medially on the pronotum, a previously unknown feature in the spider beetles and the more inclusive Bostrichoidea Latreille, 1802. This species is a probable symphile of the African species of weaver ant (Oecophylla longinoda Latreille, 1802), based on both a collection record from inside an ant nest as well as the presence of distinct trichomes on the pronotum. This taxon represents the first record of a spider beetle associated with weaver ants.


INTRODUCTION
Though a relatively small group containing only about 600 species, the spider beetles (Ptininae Latreille, 1803) are highly diverse both in morphology as well as life histories. South Africa is currently home to some of the greatest spider beetle diversity in the world, containing 13 endemic and three widespread genera and 59 described species, as well as a few introduced taxa (for the most recent works, see Irish 1996;Philips & Foster 2004;Borowski 2006aBorowski , b, 2009aBell & Philips 2008;Akotsen-Mensah & Philips 2009;Smiley & Philips 2011;Trimboli & Philips 2011;Wood & Philips 2013;Philips & Dickmann 2018;Gearner et al. 2019a, b).
While most spider beetles feed on dung and accumulated organic matter, many alternative lifestyles have evolved as well (Philips & Bell 2010). Myrmecophily, or an association with ants, appears to have evolved independently multiple times in the group (Philips 2001, Mynhardt 2012. The biology of these taxa is largely unknown with the exception of a laboratory observation in which an adult of Gnostus floridanus Blatchley, 1930, solicited and received food from a host ant (Crematogaster ashmeadi Mayr, 1886) via trophallaxis (Thomas et al. 1992).
In 1904, Péringuey described the species Ptinus elegans based on a specimen collected in KwaZulu-Natal, South Africa in 1899. Soon after however, this name was noted to be a junior homonym of the Chilean species Ptinus elegans Solier, 1849 and renamed by Pic (1906) as Ptinus natalensis. No additional specimens were discovered until more recent collections in 1981 and 2014 of single specimens. The former record is notable as an individual was discovered inside a weaver ant nest (Oecophylla longinoda Latreille, 1802). There are only two documented cases of beetles associated with weaver ants, both with the Southeast Asian and Australian species, Oecophylla smaragdina Fabricius, 1775. Adult Campsiura nigripennis Schaum, 1841 (Scarabaeidae Latreille, 1802, Cetoniinae Leach, 1815) were observed intruding nests likely to feed on ant brood, and Habroloma myrmecophila Bílý, Fikáček & Sípek, 2008(Buprestidae Leach, 1815 inhabit and mine leaves from weaver ant nests in the larval stage (Bílý et al. 2008;Komatsu et al. 2014 ).
Examination of Ptinus natalensis led the authors to conclude that this species belongs in its own genus as it is well outside the current concept of Ptinus Linnaeus, 1766, or any of its subgenera and shows much closer affinity to other ptinid genera. Herein this new genus is described, the distribution documented, and relationships and probable biology discussed.

MATERIAL AND METHODS
This study was based on the examination of three specimens, including the type, from the following collections: Iziko South African Museum, Cape Town (SAM) and the National Collection of Insects, Pretoria (SANC

Pronotum
Two thin longitudinal ridges positioned on either side of midline; two lateral tubercles on either side of the pronotum, flanking a transverse groove, basally forming a large posterior flat U-shaped depression with sides diverging anteriorly; anterior margin with deep irregular punctures.

Elytra
With longitudinal rows of punctures; interpuncture rows of small setae; scattered scale-like setae.

Abdominal ventrites
First three ventrites large, each as long or longer than 4 th and 5 th combined, fourth very short, fifth smaller than first three but much longer than fourth. Sutures visible between all ventrites; fifth ventrite distinctly transversely concave.

Sexual dimorphism
Male antennomeres 6-11 distinctly more elongate than those of the female. Eye size in both sexes approximately equal.

sPecies redescriPtion Body
Color dark brown to black on head, pronotum, and elytra. Body small and elongate. Length 3.4 ± 0.33 mm (n = 3).

Head (Fig. 2)
Head covered in punctures, large shallow irregular and contiguous mediolaterally, medially finer, longitudinally elongate; scattered, white small appressed scales; antennae dark brown, antennomeres 1-8 with moderately dense white appressed scales, first antennomere largest, second small as long as wide, remaining antennomeres longer than wide.

Pronotum
Pronotum mostly smooth with very fine alutaceous sculpture, glabrous except anterior ¼ with round and elongate scattered punctures; pair of medial vertical ridges approximately broadly rounded from anterior to posterior dorsal edge, then declivous to base just past middle, short thin yellow setae scattered on top of ridges; three tubercles on each lateral edge, anterior tubercle rounded, middle concave triangular, somewhat ear-shaped, posterior tubercle small, pointed, recumbent clumped orange trichome setae on lateral edge in between and around tubercles; a broadly rounded U-shaped smooth impression; posterior margin of pronotum narrow anterior of scutellum.

Elytra
Elytral surface covered in rows of round to elongate punctures separately longitudinally by half or less their length, puncture rows separated by about 1.5-2.0 times their diameters, 1 st and 2 nd rows slightly obliquely oriented, 3 rd and 4 th less so; humeral angles raised; scutellum triangular, lateral edges below elytral surface; interpuncture rows of small recumbent dull pale orange setae; white scales forming an irregular transverse band at anterior 1/3, extending medially in an irregular longitudinal band from anterior transverse band to posterior 1/3, lateral clump of setae on each elytron at about posterior 1/3, transverse band of setae at apex and sometimes extending anteriorly along suture.

Ventrites
Ventral surface reddish to dark brown, covered in small white appressed scales mostly covering surface; proventrite smooth, mesoventrite with irregularly shaped, glabrous indentation at middle; lateral edge of fourth ventrite and apical edge of fifth ventrite with scattered fine yellowish setae.

Legs
Legs reddish to dark brown, covered in white scales as on ventral surface; 1 st tarsomere longer than wide, others short in length and width, internal surface of tarsomeres covered in fine gold recumbent setae.

Sexual dimorphism
Antennomeres 6-11 in the maledistinctly more elongate compared to those seen in the female. Male genitalia with elongate narrow parameres with a thick median lobe that is about the same length as the parameres.

discussion
There is little doubt that Notaferrum n. gen. shares close common ancestry especially with Silisoptinus Pic, 1917(see Bellés 1988, 2009) and more distantly with Eutaphrimorphus Pic, 1898 (see Bellés 1992). All three genera are hypothesized to compose a single monophyletic lineage based on the possession of a very distinct and similarly shaped large medial smooth and flattened U-shaped shallow depression with a broadly rounded posterior border located medially at the base of the pronotum. Further similarity in these three genera is the anteriorly expanded prosternum that covers in part the ventral portion of the head, a feature that may have evolved to help protect mouthparts, most likely from ants. There are additional taxa from the Americas and southeast Asia (e.g. Prosternoptinus Bellés, 1985, andSundaptinus Bellés, 1991) that also share this feature but based on other characteristics are not closely related (Mynhardt et al. unpublished). Another similarity between Notaferrum n. gen. and Silisoptinus is the greatly reduced fourth abdominal ventrite (c. ¼ the length of the third). Further is the strong declivity on the third ventrite that slopes dramatically down to the fourth. In contrast, Eutaphrimorphus has a more typical spider beetle abdomen with the fourth reduced (c. half the length of the third) and the ventrites are all in roughly the same plane. Notable differences of Notaferrum n. gen. with the other two genera is the lack of two short knobs near the pronotal base positioned laterally. They are very pronounced in Eutaphrimorphus while in Silisoptinus they are smaller and of various shapes depending upon the species. Eutaphrimorphus has two additional knobs positioned more centrally as well. These additional projections are also seen in at least one species of Silisoptinus but are much less pronounced and relatively gently rounded.
Both Notaferrum n. gen. and Silisoptinus also exhibit depression(s) on the ventral surface that are lacking in Eutaphrimorphus; in Notaferrum n. gen., it is located only on the metaventrite near the middle and is similar to at least two other species of Silisoptinus (Bellés 1988) including one undescribed (Philips unpublished). But the two described species of Silisoptinus also have a single depression on the abdomen while two undescribed (Philips unpublished) have either only a single depression on the metaventrite or both very weakly developed depressions on both the metaventrite and abdomen. Silisoptinus species are known from the eastern side of the African continent (Zanzibar and Socotra Islands) as well as Ghana (Philips unpublished) while Eutaphrimorphus is known only from South Africa.
Also possibly related to Notaferrum n. gen. is Dignomus Wollaston, 1862, and the flightless Pseudomezium Pic, 1897, with the latter representing a flightless Dignomus (Philips unpublished and see Smiley & Philips 2011). These genera together with Silisoptinus and Eutaphrimorphus may form a monophyletic clade or at least with some close common ancestry. Dignomus as currently defined has a diverse set of pronotal modifications (Bellés 1996;Smith & Philips unpublished) and may not form a monophyletic clade. But the overall similarity of the pronotum having an anterior and posterior lobe laterally and without much lateral projection in both Notaferrum n. gen. and Dignomus (plus Pseudomezium) is notable.
distribution Notaferrum natalensis n. gen., n. comb. is known only from KwaZulu-Natal province in South Africa (Fig. 4). The current range is a little over 300 km in length, and all records are within 30 km of the coast. This distribution is within the Maputuland-Pondoland-Albany hotspot, one of three biodiversity hotspots in South Africa. Maputuland-Pondoland-Albany is notable in particular for its high plant endemism and is the second richest floristic region in South Africa (Myers et al. 2000). As the distribution of the weaver ant Oecophylla longinoda extends from Southern Africa through Eastern and Western Africa (Bolton 1995), one might expect the distribution of Notaferrum natalensis n. gen., n. comb. to be much larger. biology Notaferrum natalensis n. gen., n. comb. is hypothesized to be a myrmecophile, as one individual was collected in a weaver ant nest (Oecophylla longinoda, Fig. 3B). There are no other spider beetles known to be associated with Oecophylla ants anywhere in the world. Only one other southern African genus appears to be a true symphile; Diplocotidus Péringuey, 1899 includes three species currently known from South Africa and Namibia (Bell & Philips 2008). Unlike this new genus, species are wingless and found in arid or semiarid regions and are associated with ground nesting ants. The food type of Notaferrum natalensis n. gen., n. comb. is unclear, but it may feed on nest detritus, as most species of spider beetles feed on accumulated organic matter, particularly dung and detritus.