A revision of the genus Kaszabister Mazur (Histeridae, Histerinae, Exosternini)

Abstract We revise the four species of Kaszabister Mazur, 1972, one of which, Kaszabister barrigai sp. n., is described as new. The other species in the genus are Kaszabister rubellus (Erichson, 1834), Kaszabister ferrugineus (Kirsch, 1873) and Kaszabister carinatus (Lewis, 1888). The species are principally known from the subtropics of South America, with one in Central America. Lectotypes are designated for Kaszabister rubellus and Kaszabister ferrugineus, and a key is provided for all the species. Ants of the genus Solenopsis Westwood, mainly Solenopsis invicta Buren and Solenopsis saevissima (Smith), are documented as hosts of three of the four species.


Introduction
The genus Kaszabister Mazur, 1972, was initially described for a single species, now known as K. rubellus (Erichson, 1834), and assigned to the myrmecophilous and termitophilus subfamily Haeteriinae. Later, two other species originally described in other genera (Epierus ferrugineus Kirsch, 1873, and Phelister carinatus Lewis, 1888) were moved here, and the entire genus was moved to Histerinae: Exosternini (Mazur 1997). This dynamic taxonomic history underscores the enigmatic nature of this genus, and its affinities within the tribe remain unclear. Similarly, little is known about the biology of these species, although it has become clear that they live as guests in the nests of fire ants of the genus Solenopsis Westwood. These ants are a major nuisance as a result of invasion into many tropical and subtropical climates (Hölldobler and Wilson 1990). It is therefore important to better understand the commensal predators that may play a role in controlling ant populations.
This paper represents the first installment of an ongoing revision of all the species of New World Exosternini. The fauna is large and complex, with the limits of most genera poorly understood. Kaszabister is among the more straightforward and clearly monophyletic groups, and preliminary analyses (Caterino et al. in prep) indicate that it lies outside any other named genus. Thus we are confident in retaining its status as a genus.

Materials and methods
The morphological terminology used is that defined by Wenzel and Dybas (1941), supplemented by Helava et al. (1985), Ôhara (1994) and Lawrence et al. (2011). Following histerid conventions, total body length is measured from the anterior margin of the pronotum to the posterior margin of the elytra (to exclude preservation variability in head and pygidial extension), while width is taken at the widest point, generally near the elytral humeri. Type material of all valid species was examined by one or more of the authors. Photographic imaging was done using a Visionary Digital's 'Passport' portable imaging system, which incorporates a Canon D7 with MP-E 65mm 1-5X macro zoom lens. Images were stacked using Helicon Focus software. SEM imaging was done on a Zeiss EVO 40 scope, with most specimens sputter coated with gold. Photographs of all type specimens are available through the Encyclopedia of Life (www.eol.org).
Specimens from the following institutions were utilized:
Description. Body length 1.7-2.3mm, width 1.3-1.7mm, oval or oblong, more or less convex, reddish brown, glabrous. Head: Frons bordered by a prominent, moderately to strongly carinate frontal stria; antennae inserted under the rim of the frons in front of eyes; antennal scape slightly setose; antennal club oval, tomentose, lacking sutures or annuli, with small oval subapical sensoria on upper and lower surfaces; epistoma flat to convex, bordered by striae or carinae; labrum short, broad, rounded at sides and emarginate at middle; mandibles with strong furrows along lower outer margins and very weak subapical teeth on incisor edge; gena setose and weakly depressed; gular sutures impressed; submentum with numerous fringed setae, projecting slightly between maxillar bases; mentum about one-fourth broader than long, sides rounded, tapering apically, margin faintly emarginate; palpi relatively short, with truncate apices. Pronotum: pronotum widest at base, sides rounded, anterior angles acute; prescutellar impression absent; gland openings annulate, situated about one-third from anterior margin, behind inner edge of eye on each side; with 3 pores along each side; marginal stria complete, continuous with anterior marginal stria; lateral stria absent. Elytra: Dorsal striae of elytra simple or carinate, variously abbreviated; dorsal stria 1, subhumeral striae, and epipleural stria carinate and convergent apically. Prosternum: Antennal cavities of the prosternum visible in ventral view, located in the anterior angles of pronotum; prosternal lobe short, broad, reaching hypomeron laterally, with marginal stria at least medially; base of prosternal keel weakly emarginate; with complete carinate striae diverging anterad and posterad, not joined. Mesoventrite: Disk flat, weakly projecting at middle, with complete marginal stria; mesometaventral stria present, angulate forward onto mesoventral disk. Metaventrite: Metaventral disk with postcoxal and lateral striae, both extending laterad toward metepisternum. Abdomen: Propygidium short, moderately convex, with annulate gland openings in anterolateral corners; pygidium lacking apical stria; abdominal ventrite 1 with one or two lateral striae; ventrites 2-5 with or without posterior marginal striae. Legs: Protrochanter with seta; protibia lacking teeth, but with 8-10 stout marginal spines; protibial spurs short, strong; protarsus with fine ventral spines, pretarsal claws simple and equal; meso-and metatrochanters lacking setae; mesoand metatibiae nearly parallel-sided, the former with few weak marginal spines; mesoand metatarsomeres with single pair of apicoventral setae. Male: Eighth tergite with accessory sclerites, shallowly narrowly incised at subtruncate apex, with basal membrane attachment distad basal emargination; ventral apodemes of 8 th tergite broadly rounded, not meeting at midline; 8 th sternite approximately parallel-sided, halves not joined along midline, with apical guides gradually more strongly elevated toward apices; 9th tergite with median emargination deep, ventral apodemes situated just behind midpoint, strongly toothed; spiculum gastrale (9 th sternite) narrowed in distal two-thirds, with thin apical arms and short median apical flanges; halves of 10 th tergite well developed, separated along midline. Female: Eighth tergite forming a single, apically emarginate plate; 8 th sternite divided into two lateral plates, with thin, separate basal baculi which are articulated with the disk of S8; 9 th sternite present, elongate, connected to apex of S8; tenth tergite present, without basal apodemes; valvifers elongate, enlarged basally; coxites with two strong and one weak inner tooth; gonostyle present, free, setose; bursa copulatrix small; spermatheca short, sclerotized, forming a ventral concave disk over oviduct; spermathecal gland attached at base of spermatheca, elongate, gradually expanded to apex.
Distribution. The distribution of the species of this genus is interestingly discontinuous, with three species concentrated in subtropical South America, and a single species from Central America, with few records from the northern half of South America.  Diagnostic description. Length 1.9-2.3mm; width 1.5-1.7mm; Frontal stria descending onto epistoma as a strong carina, epistoma strongly depressed, depression broader than in K. rubellus; fourth dorsal elytral stria present in apical half to twothirds; inner subhumeral elytral stria present in apical two-thirds; fifth elytral stria generally absent; sutural stria present in apical half; elytral ground punctures denser and  more uniformly distributed; mesometaventral stria arched forward to between one-half to one-third from anterior mesoventral margin; lateral metaventral stria strongly abbreviated mediad, ending about one-third from mesometaventral margin; inner postmetacoxal striae forming a complete, narrow arc across anterior margin of abdominal ventrite 1; abdominal ventrites 2-4 with apical marginal stria. Male: Aedeagus narrow, elongate, swollen toward base, flattened apically in lateral view.
Distribution. Known principally from the Brazilian states of Mato Grosso and São Paulo, with one record each from Argentina and Paraguay, and a single specimen found in an Argentinian grape shipment at Kennedy Airport, New York, USA.
Biology. While the majority of the type specimens say merely that they were collected from 'ant nest', there is little doubt that the hosts were Solenopsis Westwood, probably Solenopsis invicta Buren, 1972, the focus of the work of collectors Lennartz and Whitcomb . Other records specify 'fire ants', Solenopsis sp., and 'Solenopsis saevissima group' as hosts.
Etymology. This species is named for the notable Chilean collector Juan Enrique Barriga-Tuñón, who provided us with one of the first known examples of the species.
Remarks. Specimens labelled as 'São Paulo, Varzea Grande' most probably came from Vargem Grande do Sul in the same state. We were not able to find any place  called Varzea Grande in São Paulo. On the other hand, there is a town of this name that is a part of greater Cuiabá, the capital of Mato Grosso, where the fire ant researchers who collected specimens from Mato Grosso and São Paulo were apparently based. But given that we have seen specimens collected on the same day, 1.xii.1972, in 'São Paulo, Vargem Grande' (3) and 'São Paulo, Varzea Grande' (1), we suspect confusion and mislabeling for the latter locality.
Distribution. This species is restricted to Central America, from southern Mexico to Costa Rica.
Biology. As for K. barrigai, many records of K. ferrugineus from 'ant nests' almost certainly refer to Solenopsis invicta as host, while a few other labels specify S. saevis-sima (Smith). One specimen from Bahia in the Lewis collection bears a label "with an Aphaenogaster" (Formicidae). However, no host specimen is present for verification.
Remarks. Mazur (1997) cites "Phelister marginicollis Bruch, 1914" as "nom. nud. -syn. nov., Wenzel in litt.". Bruch (1914 cites this as "Phelister marginicollis Lew. in litteris". This appears to have been a species that Lewis intended to describe based on Bruch's specimens, and he indicated such to Bruch. Specimens labeled "P. marginicollis Lewis" are present in the BMNH and NMNH. However, for whatever reason, the species was never formally published, so it is indeed a nomen nudum. In Bruch's later works (e.g., 1935) he apparently realized that the species was not properly described and omitted it from his catalog.
Remarks. The synonymy of K. mahunkai Mazur with Epierus rubellus Erichson was originally designated by Mazur (1984) (citing "Wenzel, in litt."). We have not studied the type of K. mahunkai first-hand, but Ottó Merkl of the HNHM very kindly compared the type specimen with our descriptions, keys and figures, and had no doubt that the synonymy is valid. His study also confirmed that Wenzel had compared types of K. mahunkai and E. rubellus side-by-side in coming to his original conclusion that the two were conspecific.

Discussion
Collecting records indicate that most of the species are strongly or exclusively associated with fire ants in the Solenopsis saevissima species group (excepting K. carinatus for which no ecological data is available). Most specimens appear to have been washed out of host mounds, and there have been no reported observations of any behavioral interactions of the Kaszabister beetles and their hosts. As all known histerids are predaceous (Kovarik and Caterino 2005), there can be little doubt that the beetles prey on their hosts, probably the larvae and pupae. From some focused collecting it appears that the density of these beetles can be relatively high, and it's conceivable that they provide a significant level of natural control of fire ant populations. Significant interest and resources have focused on introduction of parasitic flies as natural enemies of invasive fire ants in the United States (Callcott et al. 2011). None, to our knowledge, has considered predaceous myrmecophilous beetles. It should also be noted here that, although not as common a host as Eciton Latreille, Solenopsis does host other neotropical histerid genera, including Hippeutister Reichensperger and Procolonides Reichensperger (Helava et al. 1985, Kovarik and Caterino 2005, Caterino and Tishechkin 2008. Myrmecophily is a common phenomenon in Histeridae, with two entire large subfamilies (Haeteriinae and Chlamydopsinae) composed almost entirely of myrmecophiles (Kovarik and Caterino 2005). Outside these major groups, however, there have been numerous independent acquisitions of myrmecophilous habits in nearly all other major taxa. In Exosternini myrmecophily has arisen in both Old and New World genera, including Paratropus Gerstaecker, Coelocraera Marseul, Phelister Marseul, Pseudister Bickhardt and Tribalister Horn. Specialized myrmecophily is often associated with a suite of morphological specializations (Helava et al. 1985, Kovarik andCaterino 2005). Of these, only exaggerated striae/carinae (frontal, pronotal, elytral) present themselves in Kaszabister.
Kaszabister exhibits a largely disjunct distribution, with very few records from a large area of northern South America. At this point it seems most likely that this relates to sampling effort. The vast majority of existing specimens have resulted from direct sampling of Solenopsis colonies, which has generally been focused on those areas with species that have become invasive elsewhere, primarily in southern Brazil. At the same time, fairly intensive passive trapping (flight intercept trapping and pitfall trapping) in some of these areas has resulted in no specimens (Vaz-de-Mello unpublished data, Flechtmann unpublished data). So although other parts of South America have seen significant trapping, by ourselves and others, there has been relatively little effort to collect in the appropriate ant colonies. So it remains to be seen whether Kaszabister is really more widespread but undetected in South America. This situation is very similar to that of Hippeutister (Histeridae: Haeteriinae), with species known from Central America and southern Brazil (Caterino and Tishechkin 2008). Dedicated collecting efforts in Solenopsis nests elsewhere may well turn up additional species in both these groups.
An extensive collecting of Kaszabister in host ant colonies in 1972 in Mato Grosso has revealed some interesting facts about sympatry and syntopy of its species. Out of nine localities where K. barrigai was collected, at six K. ferrugineus was also found. Moreover, collecting colony codes reveal that both species have been collected in the same nests at Cáceres, Cuiabá, Mato Grosso Co., and Poconé. At the six localitites where both species were found K. barrigai was much more common, outnumbering K. ferrugineus by 100 to eight specimens. The situation at another locality, Arenapolis, was completely reversed: 23 specimens of K. ferrugineus were found in three nests there but no K. barrigai specimens are known from that site. Although nothing else known about this remarkable syntopy, the abundance patterns are suggestive of either interspecific competition, or very fine habitat and/or host preferences. Kaszabister ferrugineus and K. rubellus are also known to co-occur in at least one location; both were collected at Rosas, Argentina, represented by seven and six specimens, respectively. However, due to poor labeling, it is unclear whether they coexist microsympatrically or simultaneously, e.g. in the same colony or at the same time. This would be interesting to explore further.
The phylogenetic position of Kaszabister within Exosternini has never been addressed. Ongoing analyses suggest a relationship with another inquilinous and enigmatic genus, Mecistostethus Marseul, together as sister or near sister to the large genus Operclipygus Marseul. However, some of the morphological characters these share may be convergences related to myrmecophily. Final analyses remain ongoing, and a confident result with respect to Kaszabister will probably have to await the availability of molecular sequence data.