Bioacoustics of Ligyrus

Phylogenetic relationships. Ligyrus ( sensu Morón & Grossi 2015 ) was found as a heterogeneous group of three subgenera Ligyrus ( sensu stricto ), Anagrylius , and Ligyrodes , which coincided in part with the Casey (1915) subgenera. Ligyrus ( sensu stricto ) is paraphyletic with respect to Oxygrylius as its species are closely related, especially those from North America. Taxonomic remarks. Burmeister (1847) described the genus Ligyrus to group some species of Heteronychus and Podalgus with a kind of stridulatory apparatus on the inner surface of the elytra, which is not found in other Dynastinae . Casey (1915) separated the group in three genera ( Ligyrus , Ligyrodes , and Oxygrylius ) and several subgenera as shown in Table 1. Then, Endrödi (1969) presented a different classification using part of the Casey subgenera for Ligyrus and considering Oxygrylius as a different genus. The name Ligyrus was maintained as a valid name for more than 150 years until Ratcliffe (2003) revalidated the name Tomarus by having priority over Ligyrus , and his proposal was widely accepted. Morón & Grossi (2015) separated the genus into Ligyrus and Tomarus , grouping the species by the number of mandibular teeth, and presence of a pronotal fovea. Ligyrus ( sensu Morón & Grossi 2015 ) coincides only in part with the classification presented in this work. Oxygrylius has been treated as a separate genus for most authors except Hardy (1964) , who considered it a synonym of Bothynus (name used erroneously for species of Ligyrus ). Hardy (1964) found a specimen of L. gibbosus with triangular apex as in Oxygrylius , and so he thought it could be caused by a mutation in a single character. That is consistent with the results of the cladistic analysis, as there are many other characters supporting the grouping of these two species with Ligyrus , particularly with Ligyrus ( sensu stricto ) ( i.e. , presence of frontoclypeal carina, mentum triangular, galea rectangular, coxite strongly concave, structure of the stridulatory apparatus, shape of accessory lamella, etc .).

Diagnosis. Ligyrus can be differentiated from other Pentodontini by the following: frontoclypeus with carina or tumescences; antennal club long to very long (1.5–2.0 times as long as antennomeres 2–7); mentum triangular to subrectangular ( Fig. 2A–E ); ligula narrow to wide; ligular lobes fused or not, with a narrow emargination; galea with 3–6 teeth ( Fig. 3A–C ); pronotum with apical marginal bead complete; pronotal tubercle small to large; fovea deep, oval to triangular or absent; metepisternum with long setae; protibia tridentate, with or without additional denticles, basal tooth distant from others ( Fig. 11C–G ); protarsus of male simple or enlarged ( Fig. 10C ); internal sac with copulatory lamella and lamellar spiny belt, accessory lamellae simple ( Fig. 21C–E ); surface of coxite flat to strongly concave ( Fig. 13C–G ); and stridulatory apparatus consisting of a diagonal strip of short, transverse, parallel carinae on apex of sternite IV ( Fig. 8B–C ) and apical inner surface of elytra with transverse small tubercles forming parallel lines ( Fig. 8E–F ).

Description. ( n = 5,691). Length 11.3–21.8 mm . Humeral width 5.9–11.5 mm . Head: Clypeus triangular, subtriangular, or trapezoidal ( Fig. 1C–G ). Apex of clypeus with 1 or 2 triangular to transverse teeth, not or slightly separated. Ocular canthus rounded to acute, with or without ventral setae, without dorsal setae. Frons with tumescences or high carina, entire or interrupted at middle. Mentum triangular to subrectangular ( Fig. 2A–E ); surface flat to strongly convex. Mentum and ligula separate or fused dorsally. Ligula reduced or well developed, covered with short, sparse or long, dense setae; ligular lobes fused or not. Maxillary apical palpomere 2.0–2.5 times longer than the second. Maxilla with galea rectangular (3.0–3.5 times longer than wide); with 3–6 well-developed teeth, sometimes with 1 to 2 rudimentary teeth. Mandible with 2 apical teeth and a lateral widely rounded lobe; tooth 1 with apex acute, longer and narrower than tooth 2. Labrum subquadrate (as long as wide) to rectangular; apex rounded to slightly bilobed; with long, dense setae. Antenna with 10 antennomeres, club long to very long (1.5–2.0 times longer than antennomeres 2–7). Pronotum: Apical marginal bead complete. Apex with or without tubercle; without fovea or with deep, wide fovea. Elytra: Inner surface of apex with transverse, small tubercles forming 50–166 parallel lines. Wings: RA with dense, large peg-like setae on medial ventral region; with peg-like setae on dorsal surface ( Fig. 7B–E ). Edge of RA 3 with dense to sparse setae. Abdomen: Apex of tergite IV with a diagonal line of 9–14 short to large, transverse, parallel carinae. Sternite VIII emarginate in male; entire in female. Pygidium without rugosity. Propygidium without stridulatory area. Venter: Prosternum narrow, acute to slightly rounded. Propleura with long, dense setae on all the surface, sparser on medial area. Apex of prosternal process spherical to flat; with or without dorsal long setae. Metepisternum with incomplete, very thin carina; inner surface with deep, large punctures, with long setae; outer surface homogeneously rugose, with long, dense setae. Metasternum with small, deep, confluent punctures; with long, dense setae. Legs: Male protarsus simple or enlarged; inner claw simple or enlarged ( Fig. 10C–E ). Protibia tridentate, sometimes with denticles ( Fig. 11E ); basal tooth slightly distant from others. Metafemur with well-defined anterior row of punctures. Apical margin of mesotibia and metatibia entire to crenulate. Female genitalia: Subcoxite 1.5–2.0 times wider than long. Coxite subquadrate (as long as wide) to subrectangular (wider than long); surface flat to strongly concave. Subcoxite wider and subequal to longer than coxite. Male genitalia: Phallobase 1.2–1.3 times longer than parameres. Parameres without dorsal teeth (rarely with a dorsal long teeth), with ventral tooth. Internal sac with copulatory lamella and short to long lamellar spiny belt; accessory lamella simple (entire structure with shapes variable among the species).

Diagnosis. The subgenus Ligyrus can be differentiated by the following: Triangular to subtriangular clypeus ( Fig. 1E–G ), clypeal teeth triangular to transverse; frontoclypeus with carina entire or interrupted at middle ( Fig. 1E–G ); mentum triangular ( Fig. 2B–D ); mentum and ligula separate; ligula reduced; covered with short, sparse setae; ligular lobes fused; galea with 3–4 well-developed teeth, sometimes with 1–2 rudimentary teeth ( Fig. 3C, G, H ); antennal club very long; pronotum with or without fovea or tubercle; protibia tridentate, basal tooth slightly distant from others ( Fig. 11F–G ); protarsus of male simple, inner claw simple; internal sac with copulatory lamella and short to long lamellar spiny belt; accessory lamella irregular ( Fig. 21E ); stridulatory apparatus consisting of a diagonal line of 9–11 short to large, transverse, parallel carinae on apex of sternite IV and apical inner surface of elytra with transverse small tubercles forming 50–115 parallel lines.

Description. ( n = 4,381). Length 11.3–18.0 mm. Humeral width 5.9–10.0 mm. Head: Clypeus triangular to subtriangular ( Fig. 1E–G ). Apex of clypeus with 1 or 2 triangular teeth, not or slightly separated. Ocular canthus rounded to acute, with ventral setae, without dorsal setae. Frons with carina, entire or interrupted at middle. Mentum triangular ( Fig. 2B–D ), surface flat to strongly convex. Mentum and ligula separate. Ligula reduced, covered with short, sparse setae; ligular lobes fused, apex straight. Maxillary apical palpomere 2.0–2.5 times longer than the second. Maxilla with galea rectangular (3.0–3.5 times longer than wide) ( Figs. 3C , 4D–E ); with 3–4 well-developed teeth ( Fig. 3H ), sometimes with 1–2 rudimentary teeth ( Fig. 3G ). Mandible with 2 apical teeth and a lateral widely rounded lobe ( Fig. 5D–E ); tooth 1 with apex acute, longer and narrower than tooth 2. Labrum subquadrate (as long as wide); apex rounded to slightly bilobed; with long, dense setae ( Fig. 6A–B ). Antenna with 10 antennomeres, club very long (2 times longer than antennomeres 2–7). Pronotum: Anterior marginal bead complete. Apex without tubercle or with acute tubercle; without fovea or with deep, wide fovea. Elytra: Inner surface of apex with transverse small tubercles forming 50–115 parallel lines ( Fig. 8E–F ). Wings: RA with dense, large peg-like setae on medial ventral region ( Fig. 7E ); with peg-like setae on dorsal surface. Edge of RA 3 with dense to sparse setae. Abdomen: Apex of tergite IV with a diagonal line of 9–11 short to large, transverse, parallel carinae ( Fig. 8B–C ). Sternite VIII emarginate in male; entire in female. Pygidium without rugosity ( Fig. 9C–E ). Propygidium without stridulatory area. Venter: Prosternum narrow, acute to slightly rounded. Propleura with long, dense setae on all the surface, sparser on medial area. Apex of prosternal process spherical to slightly oval, with dorsal, long setae. Metepisternum with incomplete, very thin carina; inner surface with deep, large punctures, with long setae; outer surface homogeneously rugose, with long, dense setae. Metasternum with small, deep, confluent punctures, with long, dense setae. Legs: Male protarsus simple; inner claw simple. Protibia tridentate; basal tooth slightly distant from others ( Fig. 11F–G ). Apical margin of mesotibia and metatibia entire ( Fig. 12E–F ). Female genitalia: Subcoxite 1.5–2.0 times wider than long ( Fig. 13E–G ). Coxite subquadrate to subrectangular; surface flat to strongly concave. Subcoxite 2 times wider and longer than or subequal in length to coxite. Male genitalia: Phallobase 1.2–1.3 times longer than parameres. Parameres without dorsal teeth (rarely with a dorsal long tooth), with ventral tooth. Internal sac with copulatory lamella and short to long lamellar spiny belt; accessory lamella irregular ( Fig. 21E ).