Ambrysus scalenus La Rivers

Reynoso-Velasco, Daniel & Sites, Robert W., 2025, Revision of the Ambrysus signoreti Stål species complex (Heteroptera: Naucoridae: Ambrysinae). Section 3., Zootaxa 5735 (1), pp. 1-66 : 42-45

Ambrysus scalenus La Rivers

( Figs. 26–28 )

Ambrysus scalenus La Rivers 1953a : Univ. Kans. Sci. Bull., 35: 1313–1314 (original description).

Supplemental description. Female. Mediosternite VII (SGP) asymmetrical; left lateral margin with broad, plate-like, and apically truncate lobe at mid-length; right margin without lobe; left posterolateral corner poorly developed, blunt; right posterolateral corner well-developed, pointed; central lobe indistinctly concave medially, giving the appearance of a truncate lobe, at same level as right posterolateral corner ( Figs. 26B , 27B ).

Male. Accessory genitalic process of tergum VI (AGP) curved to right at approximately 40 degrees close to proximal third, angled again at approximately 70 degrees at distal third ( Fig. 26C ). Medial lobes of tergum VIII (pseudoparameres) symmetrical, posterolateral and posteromesal corners broadly rounded, posterior margin distinctly concave ( Fig. 26D ). Phallosoma elongate, linear, slender, tapering dorsoapically; endosoma apically sclerotized on left side, subtriangular, granulose ( Fig. 26E black arrow); left endosomal sclerite subtriangular, with denticles; right endosomal sclerite knob-like, with denticles ( Fig. 26E ). Parameres symmetrical, almost as long as maximum width, mesal margin almost straight. Proctiger almost as long as width at base. Pygophore with elongate setae sparsely distributed over most of surface, with thick brush of elongate setae on posterior margin ( Fig. 26F ).

Diagnosis. Ambrysus scalenus can be easily distinguished from other species in this section by the distinctly asymmetrical female SGP with a broad, plate-like, and apically truncate lobe on the left margin. Additionally, the posterolateral corners are asymmetrical and the central lobe is almost truncate ( Fig. 26B ). Also, males exhibit the phallosoma with the endosoma apically sclerotized on the left side, right endosomal sclerite knob-like, and left endosomal sclerite subtriangular; both sclerites with conspicuous denticles ( Fig. 26E ). Furthermore, specimens of A. scalenus present a characteristic pattern profusely marked with dark dots over reddish areas on the scutellum and reddish marks at the lateral margin and posterolateral angle of the corium ( Fig. 26A ).

Comparative notes. Within this section, females of A. sitesi also exhibit a broad lateral lobe at mid-length on the left margin of the SGP; however, this lobe is evenly rounded and less extended laterally. The condition of the male endosoma in A. scalenus is comparable to that present in A. altiplanus , A. inecol , and A. magniceps ; however, this feature is subtriangular in A. scalenus , lobe-shaped in A. altiplanus , and digitate in the other two species. The dark-spotted pattern on the corium is to some extent similar to that exhibited by A. harmodius La Rivers (Section 2).

Discussion. Ambrysus scalenus measures 10.08–12.00 in length and 6.72–7.68 in width. The distinct dark-spotted pattern on the corium confers a resemblance to the Costa Rican A. harmodius ; nonetheless, differences in the shape of the female SGP and male pseudoparameres and AGP suggest these two species are not closely related. Based on the shape of the male pseudoparameres and overall appearance, this species could be closely related to A. hydor and A. occidentalis . The Bayesian inference approach in the phylogenetic study by Reynoso-Velasco & Sites (2021) recovered A. scalenus as sister to a clade with five species, including A. hydor and A. occidentalis .

Variation. The lobe on the left margin of the female SGP can be rounded apically. Additionally, the right posterolateral corner can be blunt.

Type locality. Mexico: Michoacán: Mpio. Uruapan, El Sabino .

Repository. Male holotype ( Fig. 27A ) is housed at the SEMC.

Published records. MEXICO: Estado de México, Guerrero, Michoacán, Oaxaca, Puebla ( La Rivers 1953a; Reynoso-Velasco & Sites 2016a, 2018a, 2018b, 2019b; Reynoso-Velasco 2021a).

Distribution. This species is distributed exclusively in central Mexico, in Estado de México, Guerrero, Michoacán, Oaxaca, and Puebla ( Fig. 28 ). Distribution records of Ambrysus scalenus , all below 2,000 meters, are exclusively within the Balsas Basin biogeographic province; thus, this species is considered to be endemic to this province. The species has not been reported from Morelos, but this state is within the upper section of the Balsas Basin; consequently, the species is expected to also be distributed in this state.

Type material examined. HOLOTYPE ♂ (by original designation): MEXICO: Michoacán: Mpio. Uruapan, El Sabino , [prob. Río Cajones], 28-VII-1936, H.D. Thomas coll. / Ambrysus scalenus La Rivers HOLOTYPE. PARATYPES: same data as holotype but / Ambrysus scalenus La Rivers Paratype ( 3♂, 4♀ EMEC; 53♂, 67♀ SEMC); same but / Ira La Rivers Collection bequeathed to the California Academy of Sciences - 1978 ( 6♂, 8♀ CAS) .

Additional material examined. MEXICO: Estado de México: Mpio.Amatepec, Las Adjuntas, Río San Felipe , 05-Mayo-2008, Novelo & Cuevas colls. ( 1♀ UMC) ; [Mpio. Tejupilco], Acamochitlan, El Zapote, [El Zapote de Acamuchitlán], 21-XI-1984, H. Brailovsky / Colección del Instituto de Biología , UNAM, México D.F. / C.J. Drake Accession ( 2♀ USNM) ; [Mpio. Tejupilco], Bejucos, Río Bejucos , 700 m, 22-Abr-2004, R. Novelo coll. / Ambrysus sp. R. Novelo det. 2004 ( 4♂, 1♀ UMC) ; [Mpio. Tejupilco], Bejucos, Río Bejucos , 1950’, 22-IV-2004 / William D. Shepard, leg. ( 1♀ EMEC) ; [Mpio. Tejupilco], Bejucos, Temascaltepec, 3-VII-1933 / H.E. Hinton & R. L. Usinger colls. / Ira La Rivers Collection Bequeathed to the California Academy of Sciences ( 1♂ CAS) ; Mpio. Tejupilco, Paso de Vigas, Arroyo Paso de Vigas , 18º53’32.6’’N, 100º13’57.0’’W, 1107 m, L-1459, 19-Dec-2012, Reynoso-Velasco coll. ( 6♂, 1♀ UMC) ; same but 5-Apr-2015, L-1909, Reynoso-Velasco, Sites, Shepard & Barr colls. ( 1♂, 1♀ CNIN; 1♂, 1♀ IEXA; 2♂, 2♀ UMC) ; [Mpio Tonatico], Tonatico, VII-1961 / Colección del Instituto de Biología , UNAM, México D.F. ( 1♂ CNIN, 1♀ IEXA) ; Tejupilco, Mex., Temascaltepec , 24-VI-1933 / H.E. Hinton & R. L. Usinger colls. ( 1♂ CAS) ; same but 17-VI-1933 / Ira La Rivers Collection Bequeathed to the California Academy of Sciences ( 1♀ CAS) . Guerrero: Km 154 carr. Iguala –C[iu]d[ad] Altamirano , 23-XI-1984, H. Brailovsky coll. / Colección del Instituto de Biología , UNAM, México D.F. ( 1♀ CNIN) ; same but / C.J. Drake Accession ( 1♀ USNM) ; same but E. Barrera coll. ( 1♂, 1♀ USNM) ; [ Mpio. Eduardo Neri ], 9 mi N of Zumpango, 8-Jan-1956, J.C. Shafftner / Prop. of J.C. Shafftner / C.J. Drake Accession ( 2♂ USNM) ; Mpio. Teloloapan, km 20 carr. Teloloapan-Apaxtla de Castrejón, nr. Tepozanalquillo , 18º14’26.8’’N, 99º54’51’’W, 1083 m, 29-Dec-2012, L-1497, Reynoso-Velasco coll. ( 1♀ UMC) ; Ruta El Caracol, approx.. km 38 Teloloapan, 22-X-1988, J. Bueno coll. / Colección del Instituto de Biología , UNAM, México D.F. ( 1♀ IEXA) . Michoacán: Mpio. Buenavista, Buenavista Tomatlán , 19º12’57.8’’N, 102º34’30.2’’W, 440 m, 24-Dec-2012, L-1481, Reynoso-Velasco coll. ( 2♀ UMC) ; Mpio. Carácuaro, Río San Diego at Carácuaro , 19º01’04.8’’N, 101º07’33.2’’W, 519 m, 22-Dec-2012, L-1473, Reynoso-Velasco coll. ( 1♂ UMC) ; Mpio. La Huacana, La Huacana, Colonia Lázaro Cárdenas , 18º57’19’’N, 101º48’43.2’’ W, 458 m, L-1478, 23-Dec- 2012, Reynoso-Velasco coll.( 1♂, 1♀ UMC) ; Mpio.Nocupétaro, San Antonio de la Huerta ( Melchor Ocampo ), 19º02’ 04.4’’N, 101º15’07.9’’W, 624 m, 22-Dec-2012, L-1475, Reynoso-Velasco coll. ( 1♂ IEXA) ; Mpio. Tepalcatepec, Los Horcones, Pte. Pinolapa at km 31 carr. Tepalcatepec-Coalcomán , 19º00’31.3’’N, 103º01’25.6’’W, 554 m, 25- Dec-2012, L-1484, Reynoso-Velasco coll. ( 3♂, 2♀ UMC) ; [Mpio. Tepalcatepec], Tepalcatepec, Río Pinolapa , 16- May-2002, R. Novelo coll. ( 1♀ UMC) ; Mpio. Tuzantla, Río Tuzantla at Tuzantla , 19º13’18.1’’N, 100º34’05.5’’W, 593 m, 21-Dec-2012, L-1470, Reynoso-Velasco coll. ( 1♂ IEXA) . Oaxaca: [ Mpio. Santiago Cacaloxtepec ], 12 mi SE of Huajuapan [ de León], 4-VII-1953, 6000 ft / Univ.Kans.Mex. Expedition / Slesnick Field No. 33 / Ambrysus scalenus La Rivers ( 5♂, 3♀ SEMC) ; same but / Ira La Rivers Collection Bequeathed to the California Academy of Sciences ( 1♀ CAS) . Puebla: [Mpio. Ahuehuetitla], 10 mi SE of Tehuitzingo, 3900 ft, 3-VII-1933 / Univ.Kans.Mex. Expedition / Slesnick Field No. 32 / Ambrysus scalenus La Rivers 1953 ( Ira La Rivers ) (1 indet. SEMC) .

Figures

FIGURE 26. Structures of Ambrysus scalenus La Rivers. (A) Dorsal habitus of male (last abdominal segments removed; yellow and white arrows indicate marks at lateral margin and posterolateral angle of corium, respectively), (B) sternum VI and subgenital plate of female (terminal abdominal segments removed), (C) 6th and 7th abdominal terga of male, (D) 8th abdominal tergum of male, (E) ventral surface of male phallosoma (black arrow indicates subtriangular portion of endosoma, (F) genital capsule of male (phallosoma removed). lplc = left posterolateral corner, ls = left side, rs = right side.

FIGURE 27. Ambrysus scalenus La Rivers. (A) Dorsal habitus, labels, and dissected last abdominal segments of male holotype, (B) subgenital plate and labels of female paratype (allotype).

FIGURE 28. Distribution of Ambrysus scalenus La Rivers.