Ambrysus dyticus 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 : 17-20

Ambrysus dyticus La Rivers

( Figs. 9–11 )

Ambrysus dyticus La Rivers 1953b : Pan-Pac. Ent., 29: 140–142 (original description).

Supplemental description. Female. Mediosternite VII (SGP) asymmetrical, lateral and apical lobes on right margin slightly less developed than those on left margin; margins with rounded lateral and pointed apical lobes at mid-length and apically, respectively; posterolateral corners rounded to truncate; central lobe concave medially, giving the appearance of two rounded lobes, almost at same level as posterolateral corners ( Fig. 9B ).

Male. Accessory genitalic process of tergum VI (AGP) curved to right at approximately 30 degrees close to proximal third, angled again at approximately 75 degrees at distal third ( Fig. 9C ). Medial lobes of tergum VIII (pseudoparameres) symmetrical, posterolateral corners produced and narrowly rounded, posteromesal corners broadly rounded, posterior almost margin straight ( Fig. 9D ). Phallosoma elongate, linear, slender, tapering dorsoapically; left endosomal sclerite subtriangular, with inconspicuous denticles; right endosomal sclerite knob-like, with inconspicuous denticles ( Fig. 9E ). Parameres symmetrical, almost as long as maximum width, mesal margin slightly convex. Proctiger 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. 9F ).

Diagnosis. This species can be easily distinguished from the rest in this section by the distinctive presence of pointed and conspicuous apical lobes on the female SGP ( Fig. 9B ).

Comparative notes. Ambrysus dyticus is unique among species in this complex because it is the only one with the female SGP with distinct and pointed apical lobes. Ambrysus altiplanus and A. sonorensis also present apical lobes, but they are poorly developed and inconspicuous.

Discussion. This species was reported to measure 9.50–11.00 in length and 6.75–7.50 in width ( La Rivers 1953b). At the time of its description, La Rivers considered the female SGP and male AGP of this species to be similar to those of his A. occidentalis La Rivers ; nonetheless, he did not consider these features to be an indication of close relatedness, as the two species exhibit differences in body proportions and convexity. In fact, the AGP is, to some extent, comparable between the two species, but the shape of the SGP is quite contrasting. Superficially, this species more closely resembles the Central American A. variegatus Usinger (Section 1). Recent phylogenetic studies on Cryphocricinae (Reynoso Velasco & Sites 2021) and Naucoridae ( Sites 2022) did not include A. dyticus .

The single female specimen from El Salvador in the CAS has a label that reads “ Homotype ” and was identified by Usinger as Ambrysus lundbladi Usinger (Section 2; listed in the Material examined section); this indicates the author considered this specimen to be conspecific with his species from central Mexico. This inaccurate concept could be based on an “overall” dorsal similarity of the two specimens ( A. lundbladi was described based on a single female), because the shape of the SGP is noticeably different.

Variation. In the original description and based on specimens from two localities in Guatemala, La Rivers (1953b) reported a general “quadrisinuate” posterior margin of the female SGP of A. dyticus ( Figs. 9B , 10A bottom). According to the author ( La Rivers 1953b), this generalized shape could exhibit some variation depending on proportions of the posterolateral corners and central lobe, including: 1) corners and central lobe only slightly developed ( Fig. 10B bottom); 2) corners and central lobe poorly developed and inconspicuous, giving the appearance of a truncate posterior margin ( Fig. 10C bottom); and 3) corners conspicuous and central lobe poorly developed and inconspicuous ( Fig. 10D bottom). Additionally, each of these SGP variants had its corresponding male AGP alternative form, which exhibited slight variation on the length and shape of the apex ( Figs. 10A–10D top). Based on the specimens we have examined, even when some of this variation on the posterior margin of the SGP is present, the presence of pointed apical lobes indicates the specimen belongs to A. dyticus .

Type locality. Guatemala: Santa Rosa: Lago Ayarza .

Repository. La Rivers (1953b) reported that the male holotype, allotype, and several paratypes were deposited in the SEMC; however, Andrew Short (pers. com., October 2021) informed us that the holotype is not there; only five paratypes were present. Thus, the repository of the holotype is unknown. In the original description, La Rivers (1953b) reported the type material to be deposited only in the SEMC (several specimens) and the UMMZ ( one specimen). The single specimen at the UMMZ is from 10 km SW of Cuilapa ( Guatemala). We found four specimens at the USNM from the Cuilapa locality bearing La Rivers’ A. dyticus paratype labels (see Material examined); thus, these specimens could have been donated to the USNM after the species description.

Published records: EL SALVADOR: Chalatenango, Cuscatlán; GUATEMALA: Baja Verapaz, Guatemala, Santa Rosa; HONDURAS: Francisco Morazán; MEXICO: Chiapas ( La Rivers 1953b, Herrera 2013, Reynoso-Velasco 2023). Reynoso-Velasco (2023) stated that the specimens (housed at the CAS) used by Herrera (2013) to report this species from Mexico represented misidentifications; thus, those records from the states of Jalisco and Nayarit are incorrect. Additionally, Herrera (2013) reported this species from Nicaragua, but the specimens were not found at the CAS (Reynoso-Velasco 2023); hence, this record needs to be confirmed.

Distribution. Ambrysus dyticus is a Central American species distributed from the southernmost part of Mexico to Honduras ( Fig. 11 ). Records are predominantly within the Chiapas Highlands biogeographic province, at elevations between 500 and 2000 meters.

Type material examined. PARATYPES: GUATEMALA: [ Santa Rosa]: Lake Ararza [Ayarza], 11-V-1947, M47-60, R . R . Miller ( 1♀ SEMC); same but M47-18 ( 1♂ SEMC); [Mpio. Cuilapa], 10 km SW of Cuilapa, 21-IV- [1946] / 1946 R . R. Miller / Ambrysus dyticus La Rivers Paratype ( 2♂, 1♀ USNM); same but Ambrysus dyticus La Rivers determined by Ira La Rivers ‘50 ( 1♂ USNM) .

Additional material examined. EL SALVADOR: Chalatenango: [ Mpio. La Palma], San José Sacare , 14-III-1927, R .A. Stirton coll. / Homotype / Ambrysus lundbladi Usinger det. by R . L. Usinger / Ira La Rivers Collection bequeathed to the California Academy of Sciences - 1978 ( 1♀ CAS) . Cuscatlán: [Mpio. El Rosario]. [El] Rosario , Nº444-547B, 23-III-1955, M.S. V . coll. ( 3♂, 3♀ USNM); same but Salazar coll. ( 2♂, 3♀ USNM) . GUATEMALA: Baja Verapaz: [Mpio. Salamá], Río Quililá , VI-2011, R . S. Zack ( 1♂, 1♀ IEXA; 1♂, 1♀ UMC); same but Río Quililá on Rt. 5 (old road) to Salamá from Rt. CA-14, 15º13.913’N, 90º17.662’W, 1,355 m, 15-IX-2009, R . S. Zack & J. Monzón colls. ( 2♂, 2♀ UMC) . Guatemala: [ Mpio. Ciudad de Guatemala], 14 km E of Guat [emala] City, 28- III-[1946] / R . R . Miller 1946 ( 1♂ USNM); same but 18 km E of Guat [emala] City, 24-III-[1946] ( 4♂ USNM); same but 10 mi S of Guatemala City, 5-VIII-1965, Paul. J. Spangler ( 1♀ USNM); 50 km E of Guat [emala] City, 11-III- [1946] ( 2♀ USNM) . HONDURAS: Francisco Morazán: [ Mpio. San Antonio de Oriente ], El Zamorano, 14º01’N, 87º00’W, 850 m / Estudiante EAP / 77.431 ( 1 ♀ EAPZ); same but / 77.421 ( 1♂ EAPZ) . MEXICO: Chiapas: [Mpio Cacahoatán]: Río Colorado [Maxaum at Pte. Colorado], 21-IV-1983, H. Brailovsky coll. / Colección del Instituto de Biología , UNAM . México D.F. / C.J. Drake Accession ( 1♀ USNM); same but E. Barrera coll. ( 1♀ USNM) .

Figures

FIGURE 9. Structures of Ambrysus dyticus La Rivers. (A) Dorsal habitus of male (last abdominal segments removed), (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, (F) genital capsule of male (phallosoma removed). al = apical lobe.

FIGURE 10. Typical shape and three variants of the posterior margin of the female subgenital plate (below) and the male accessory genitalic process (above) of Ambrysus dyticus La Rivers reported in the species original description. (A) Typical quadrisinuate shape of plate, (B) posterolateral corners and central lobe of plate only slightly developed, (C) posterior margin of plate truncate, (D) posterolateral corners conspicuous and central lobe of plate poorly developed. Modified from La Rivers 1953b.

FIGURE 11. Distribution of Ambrysus dyticus La Rivers.