Diochus cleidecostae, a new species from the Brazilian Amazon and a discussion of the sexual dimorphism on sternum VIII (Coleoptera: Staphylinidae: Staphylininae: Diochini)

Diochus Erichson is a worldwide rove beetle genus with species found in forest floor litter. Three species of Diochus were recently collected in northern Brazil, one of them considered as new and herein described. Within Diochus nanus-group, D. cleidecostae sp. nov. differs from D. apicipennis Cameron, D. nanus Erichson and D. perplexus Cameron by the aedeagus with clearing trifurcate apex of parameres; and differs from D. parvulus Kraatz by the three apical long setae of parameres distributed on ventral and dorsal lobes. A previous key to the D. nanus-group is updated to include the new species. Here we also report for the first time D. santacatarinae Irmler and D. parvulus from Pará state, Brazil. Finally, a discussion about the sexual dimorphism on sternum VIII is also provided for the genus. Key-Words. Amazon; Morphology; Neotropical; Rove beetles; Taxonomy.


INTRODUCTION
The tribe Diochini Casey includes the worldwide genus Diochus Erichson and the Chilean and Argentinian genus Antarctothius Coiffait & Saiz. The Vietnamese genus Coomania Cameron was recently removed from Diochini and now is assigned to Coomaniinae Zyla & Solodovnikov (Zyla & Solodovnikov, 2019). Here we adopt Diochini as tribe of Staphylininae following Cai et al. (2019), and not as tribe of Xantholininae, as suggested by Zyla & Solodovnikov (2019). In both above mentioned studies, Diochini is a sister-group of (Othiini (Maorothiini, Xantholinini).
The species of Diochus are found in forest floor litter and they are easily identified by the minute and aciculate apical maxillary palpomere, and the neck, which is nearly one-third the width of the head. A detailed diagnosis for the genus was provided by Smetana (1982) and Zhou & Zhou (2016). Diochus includes 78 extant species and one fossil (Chatzimanolis & Engel, 2011;. Recently, Irmler (2017) revised the Neotropical species of Diochus and allocated the 37 species in six species-groups. One of them, the Diochus nanus-group, includes four species, which share body with light colouration (yellow to light brown), antennomeres 4-10 wider than long, aedeagus with parameres widened at apex forming a large plate or with two or three lobes, and each paramere with three apical long setae (Irmler, 2017). Another group is the D. verhaaghi-group, with two species that share body brown (darker than D. nanus-group), aedeagus with parameres slightly widened at apex, not bifurcate, and each paramere with four apical setae (Irmler, 2017). Among the specimens studied by Cajaiba et al. (2017) we identified three species of Diochus belonging to the two species groups discussed above (two in D. nanus-group and one in D. verhaaghi-group). One of the species in D. nanusgroup is considered as new and herein described.
The key for D. nanus-group from Irmler (2017) is updated to include the new species. Here we also report for the first time D. santacatarinae Irmler and D. parvulus Kraatz from Pará state. Finally, a discussion about the sexual dimorphism on sternum VIII is also provided for the genus.

MATERIAL AND METHODS
The specimens were collected in the municipality of Uruará, state of Pará, in areas of primary forest, secondary forest with 15 years of regeneration, secondary forest with five years of regeneration, agriculture (cocoa plantations, Theobroma cacao L.), and pasture for extensive livestock (Figs. 1-3). The material is deposited in "Coleção Entomológica Pe. Jesus Santiago Moure", Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil (DZUP) and in the Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil (MZSP). Dried specimens were immersed in 10% potassium hydroxide overnight (about 12-15 hours), followed by a bath of acetic acid to neutralize the hydroxide and then water to remove any residue. Dissections were performed under a stereoscopic microscope, and the habitus photographs and dissected parts were illustrated using a light or stereoscopic microscope. The additional measurements follow Irmler (2017): eye length (EL), head length (HL), relative length of eyes as EL : HL ratio, width of head at posterior angles of head (PW), width of head at anterior edge of eyes (EW), and the divergence of head abbreviated as PW : EW ratio. The dissected parts were placed inside micro vials with glycerin and pinned with the respective specimens. Label information is listed in sequence from top to bottom. The data from each label are enclosed within double quotes (" "), a forward slash (/) separates lines, and information enclosed by square brackets ([ ]) provides additional details. The terminology follows Irmler (2017).

RESULTS
Twelve species of Diochus belonging to the five species groups are recorded from the Brazilian Amazon (    (2017). In the same way, Smetana (1982) and Zhou & Zhou (2016) have not discussed the male and female sternum VIII for Diochus. Smetana (1977) illustrated the emarginate posterior margin of sternum VIII of the male of D. nanus Erichson, but did not discuss it for the females. Naomi (1989) commented about the sexual dimorphism on sternum VIII in many rove beetle groups, but not explicitly for Diochus. Chatzimanolis & Engel (2011) described the fossil species D. electrus based on a female in which the sternum VIII shows no secondary sexual structures (maybe with posterior margin rounded or at least not emarginate). We believe that the sexual dimorphism on sternum VIII in Diochus is common and might also occur in other species of the genus. The specimens of D. santacatarinae studied here were found in forest litter of cocoa plantations (Theobroma ca-cao Linnaues) (Fig. 3), secondary vegetation (five and 15 years of regeneration) and native vegetation (Fig. 2).
Diochus santacatarinae was previously known from French Guiana, Ecuador, Peru and southern Brazil (Santa Catarina state). The species is recorded for the first time from Pará state, in northern Brazil. Holotype (not seen) deposited in Senckenberg Deutsches Entomologisches Institut, Müncheberg, Germany (SDEI) (Irmler, 2017).

Remarks:
The specimens from Pará, identified as Diochus parvulus, have similar aedeagus (mainly parameres) and spermatheca as those illustrated by Irmler (2017) (Figs. 10-14). However, similarly to Diochus santacatarinae, the male of D. parvulus has the sternum VIII with posterior margin emarginate at the middle, whereas the female has the sternum VIII with posterior margin broad curved and slightly acute at the middle.
The specimens of D. parvulus were collected using the winkler method in forest litter of pasture for extensive livestock and using pitfalls baited with banana in native vegetation (Fig. 2).
Diochus parvulus was previously known from Venezuela, Ecuador, Paraguay, Argentina and Brazil (from the states of Amazonas, Mato Grosso, Rio de Janeiro and Santa Catarina). The species is recorded for the first time from the state of Pará.  brown, elytra darker (Fig. 6); appendices yellowish, antennae slightly darker than other appendices; antennomere 11 with apical half lighter than basal half. Head: Head longer than wide, length 0.40 mm, width 0.34 mm; eyes prominent, 0.11 mm long; temples twice as long as eyes; EL : HL = 0.28; temples parallel, PW : EW = 1.18; posterior angles rounded. Dorsal surface of head slightly microsculptured, vertex impunctate midline, convergent row of four punctures from anterior edge of eyes to middle of vertex, postocular area and at posterior marginal area more setiferous punctures. Antennae slightly longer than head; antennomere 1 nearly as long as 2-3 combined; 2 as long as 3; 3 one-fourth longer than 4; 4-10 wider than long, with same length, slightly increasing in width; 10 around twice wider than long; 11 nearly wider than 10 and length of 9-10 combined (Fig. 20). Gular plate with sides divergent towards anterior margin. Thorax: Pronotum longer than wide, 0.50 mm long and 0.44 mm wide; anterior and posterior angles rounded; anterior third strongly convergent. Dorsal surface of pronotum glossy; adjacent to wide impunctate midline with row of three punctures; interstice between anterior pair twice as wide as interstices between posterior pairs; four additional punctures laterad; several setiferous punctures along lateral margin. Elytra wider than long, 0.44 mm long, 0.56 mm wide; sides divergent towards posterior margin; posterior margin slightly emarginate. Elytra glossy, setiferous punctures in irregular rows; first row of five punctures adjacent to suture line; two additional rows laterad; interstice between two rows on disc much closer than between row at suture and first row on disc. Hind wings developed. Tarsal formula 5-5-5; fore tarsomeres 1-4 strongly dilated; mid and hind tarsomeres 1-4 clearing decreasing in length; mid and hind tarsomeres 5 nearly the length of 3-4 combined. Female: Similar to male, except for posterior margin of sternum VIII broadly rounded; tergum IX without ventral struts; sternum IX consisting of pair of hemisternites; spermatheca small with capsule of subspherical shape; bursa copulatrix in lateral position to coiled approximately circular duct (Fig. 17).

Biological notes:
The specimens of D. cleidecostae sp. nov. were found in forest litter secondary vegetation (five years of regeneration) and native vegetation (Figs. 1, 2).

Etymology:
The specific name "cleidecostae" is formed from a personal name and treated as noun in the genitive case (ICZN, 1999, art. 31.1). The specific name honors the Brazilian coleopterologist Dr Cleide Costa, from MZSP and specialist of immature insects.