Systematics of the Neotropical genus Loxozus ( Diptera : Neriidae ) , with notes on distribution and sexual dimorphism

The monotypic genus Loxozus Enderlein, 1922 is redescribed. After examining the holotypes of Tetanocera cornuta Walker, 1853 and Loxozus clavicornis Enderlein, 1922, we confirm that these species are synonyms and reiterate that the correct name of the nominal species is Loxozus cornutus (Walker, 1853). The male of L. cornutus is described for the first time and notes on the species’ sexual dimorphism and illustrations of the genitalia are provided, together with distribution data, including new records for Venezuela, Brazil and Peru.


INTRODUCTION
The monospecific genus Loxozus Enderlein, 1922 was described from one female, L. clavicornis Enderlein, 1922, collected in the Colombian highlands (Fig. 1).Loxozus differ from other Neotropical species of Neriidae in the very oblique vein dm-cu and the thin and elongate scape and pedicel (Aczél 1961).Steyskal (1965) synonymized L. clavicornis under Tetanocera cornuta Walker, 1853 (Fig. 2), a species originally described in Sciomyzidae from a female specimen also collected in Colombia.But, in a subsequent catalogue, Steyskal (1968) recorded L. clavicornis from Bolivia, apparently disregarding that a few years before (Steyskal 1965), he had synonymized it with T. cornuta.Since the publication of the Steyskal's (1968) catalog, in which L. clavicornis was erroneously included as valid species name, the synonymy with T. cornuta has been overlooked (Mello andZiegler 2012, Sepúlveda andde Carvalho 2016).
Original descriptions of the two female holotypes, T. cornuta and L. clavicornis (Figs 1, 2), contain the only published morphological information available for the species.The only known records of the species correspond to the Colombian holotypes and several female specimens from Bolivia examined by Steyskal (1968).Here, we provide information on new material of L. cornutus, including males from different localities in South America, images of the type material and a description of male genitalia, including the first description of the phallus.The female holotypes were studied and after confirming the cospecificity with other no-type material, a redescription of the species is provided including variations among females, while variable male traits are described separately.Total length was measured from the anterior margin of the parafacial to the posterior margin of tergite 6 (excluding antenna and terminalia).Examined specimens are identified by a number, which we also included in the determination label and cited here in the material examined section in brackets, along with the acronym of the depository institution.Known distribution is indicated by country, where asterisk (*) indicates new records.Terminology used in the description of male terminalia follows Sinclair (2000).Diagnosis.Head rounded.Arista micropilose.Antennae separated by more than twice the width of scape at base.Antennal base blackish-brown and shiny; inner margin projected anteriorly over dorsal portion of face.Anterior margin of frons concave, projected anteriorly between antennal bases and beyond level of anterior margin of parafacial; frontal vitta with U-shaped yellow stripe separating it from the fronto-orbital plate.Face exposed in dorsal view between antennal bases.Vibrissa spine-like, inserted on small tubercle.Prosternum wide, joining proepisternal plate laterally.Postpronotal carina large, higher than postpronotal lobe.Mid coxa with three lateral setae.
Female (Fig. 3).Body length 5.6-8.2mm.Wing length 7.0-8.2mm and width 1.9-2.2mm; yellowish-brown with head and thorax partially yellow.One female from Venezuela is slightly paler and the Amazon specimen is the darkest.
Head.Antenna elongate, about same length as head (Fig. 4).Scape slightly constricted on basal half, length twice maximum width (Fig. 5).Pedicel narrowed, length more than three times maximum width and slightly less than twice length of scape; inner process of pedicel wide triangular (Fig. 6).First flagellomere brown with whitish micropubescence; dorsal and ventral margins parallel and apex widely rounded.Arista white, inserted dorso-apically on first flagellomere.Antennal bases conspicuously protrudent and separated medially by upper face.Frontogenal suture joins distal margin of antennal base.Fronto-orbital plate brown with white pruinescence; three short equidistant fronto-orbital setae, two anterior hair-like.Inner vertical seta almost hair-like.Ocellar triangle shiny and small.Parafacial brown and narrow (Fig. 5).Gena sub-shiny yellow and wide; genal seta spine-like.Postgena densely white pruinose with several black and white setulae.Occiput shiny brown, with wide yellow median stripe.
Thorax.Yellowish-brown pruinose with two dorsal white stripes, separated by a wide median brown stripe; pleura pruinose.Presutural scutum longer than postsutural scutum.One dorsocentral seta.Scutellum yellowish-brown pruinose with wide median yellow stripe; apical setae thick, slightly shorter than dorsal length of scutellum.Postpronotal lobe bare and yellow dorsally.Anterior notopleural seta absent, posterior notopleural seta spine-like, inserted on tubercle.Katepisternum with one short dorsal seta.Vein dm-cu very oblique (Fig. 7).Basicosta with one seta.Halter yellow, with black and orbicular knob.Coxae yellowish-brown; fore coxa with two antero-apical setae and two anterolateral setae; mid coxa with three lateral setae; hind coxa with one lateral seta.Femora brownish-yellow; fore femur with several anteroventral and posteroventral spine- like setae on distal third; mid femur with two median setae on anterior margin and anteroventral and posteroventral spine-like setae on distal third; hind femur with two dorsal distomedian setae and anteroventral and posteroventral setae on distal third.Tibiae brownish-yellow with dark apex (Fig. 3) and slightly wider distally (Fig. 8).Basitarsomere short, less than 1/4 length of tibia.
Remarks.After examining the holotypes of T. cornuta and L. clavicornis, we confirm the synonymy of these species and reiterate that the correct name of the species is Loxozus cornutus.
The only phylogenetic study of Neriidae (Koch et al. 2015), recognized two main Neotropical lineages in the family: the Eoneria-group and the Nerius-group.Although L. cornutus was not included in that study, according to the synapomorphies proposed for each of those two lineages, we hypothesize that L. cornutus is closely related to other species of the Nerius-group (i.e.strong increase in female size; presutural scutum longer than postsutural scutum; several changes in wing venation; polished and shiny antennal base; reduction in setae length; lack of occipital setae; and reduction in the number of setae on both basicosta and male fore coxae).Within Nerius-group, Loxozus, seems to be morphologically related to Nerius Fabricius, 1805 by the peculiarly wide inner process of pedicel and prosternum.Loxozus cornutus can be easily recognizable from any other neriid for its narrow and long antennae, separated by at least twice the length of the scape at base.
Half of the genera of Neriidae present sexual dimorphism, including Antillonerius Hennig, 1937 (Sepúlveda and Souza unpublished data), Indonesicesa Koçak & Kemal, 2009(Aczél 1954), Longina Wiedemann, 1830 (Buck and Marshall 2004), Telostylus Bigot 1859 (Steyskal 1966) and the species Glyphidops bullatus (Enderlein, 1922) (Sepúlveda et al. 2014) and Telostylinus angusticollis (Enderlein, 1922) (Bonduriansky 2009).In these genera, the males have elongated head and antenna and/or elongate legs with or without conspicuous spines.Males of L. cornutus can reach almost twice the size of a small female and the colors are darker in larger representatives.The male fore tibia is swollen (Fig. 10) with thick spine-like setae posteriorly (Fig. 11), conspicuously differentiated from the female thin tibia (Fig. 8).This swollen appearance of the fore leg in males is also present in other genera of Neriidae, including Indonesicesa, Longina and Telostylus.These traits play an important role in male-male competition for oviposition sites, whereas larger and stronger males will have more access to females.This sexual selection drives the evolution of the shape of the body of males (Bonduriansky 2006).
The genital morphology of L. cornutus is not very differentiated from other Neotropical Neriidae, which also present the pattern described for D. angusticollis by Bath et al. (2012): "Where the middle section (basal part of distiphallus) joins the distal section (distal part of distiphallus), both species possess a rigid spike"... "and the distal section is a long, unsclerotized, flexible tube, which is coiled up at the base of the epandrium when the genitalia are retracted".

ACKNOWLEDGMENTS
We would like to thank the three reviewers, for their thoughtful comments and suggestions to improve our manuscript.We are grateful to curators and staff of collections that sent us material.We are thankful to Daniel Whitmore (NHMUK) and Joachim Ziegler (ZMHB) for sending photographs of type material.We thank to TaxOnline, Rede Paranaense de Coleções Biológicas for the pictures and to the program Sistema Nacional de Pesquisa em Biodiversidade (SISBIOTA-Brasil) for the material collected in Brasil.We want to thank Peter Löwenberg-Neto from Universidade Federal da Integração Latino-Americana from the following institutions were exami ned for this study (abbreviations according to Evenhuis 2017): MZUSP, Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil; NHMUK, The Natural History Museum, London, United Kingdom; USNM, National Museum of Natural History, Smithsonian Institution, Washington D.C., United States of America; ZMHB, Museum für Naturkunde der Humboldt-Universität, Berlin, Germany.

Figure 13 .
Figure 13.Localities of the species of L. cornutus examined.