Ambrysus occidentalis 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 : 34-37

Ambrysus occidentalis La Rivers

( Figs. 20–22 )

Ambrysus occidentalis La Rivers 1951 : Univ. Calif. Publ. Entomol., 8: 322–325 (original description).

Supplemental description. Female. Mediosternite VII (SGP) symmetrical; margins with small and rounded lobes at mid-length; posterolateral corners small, rounded; central lobe poorly developed, shallowly concave medially, giving the appearance of two rounded lobes, at same level as posterolateral corners ( Figs. 20B , 21B ).

Male. Accessory genitalic process of tergum VI (AGP) curved to right at approximately 50 degrees at proximal third, angled again at approximately 80 degrees at distal fifth ( Fig. 20C ). Medial lobes of tergum VIII (pseudoparameres) symmetrical, posterolateral corner narrowly rounded, posteromesal corner broadly rounded, posterior margin almost straight ( Fig. 20D ). Phallosoma elongate, linear, slender, tapering dorsoapically; endosomal sclerites knob-like, right-tilted, with conspicuous denticles ( Fig. 20E ). Parameres symmetrical, slightly longer than maximum width, mesal margin convex. 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. 20F ).

Diagnosis. This species can be distinguished from other species in the section by the symmetrical SGP with small, rounded lateral lobes at mid-length of each margin. Additionally, the posterolateral corners are small and rounded and the central lobe is poorly developed and shallowly concave medially ( Fig. 20B ). Also, the male phallosoma presents both endosomal sclerites knob-like with robust denticles. It is common that both, or at least the left endosomal sclerite, are tilted to the right ( Fig. 20E ).

Comparative notes. See corresponding section in treatment of A. hydor . Additionally, another important aid to distinguish between the alike A. occidentalis and A. hydor is that the former species generally exhibits the phallosoma with both endosomal sclerites, or at least that on the left, tilted to the right. These sclerites are generally straight and basally directed in A. hydor . In general, the endosomal sclerites of A. occidentalis exhibit robust denticles, whereas A. hydor has small denticles.

Discussion. This species measures 11.00– 12.75 in length and 7.25–8.37 in width. In the original description, La Rivers (1951) reported material of this species from Baja California and Sonora, in northwestern Mexico; however, A. occidentalis was not included in the study on the Ambrysus of Mexico ( La Rivers 1953a). Additionally, as mentioned by La Rivers (1951: 325) and confirmed here, early reports of A. signoreti in the United States (e.g., some specimens from Arizona and California in the Material examined section) were sometimes based on misidentified specimens belonging to A. occidentalis .

See Discussion section in treatment of A. hydor for the reason to refrain from reporting some specimens in various collections (e.g., CAS, USNM) initially identified by DRV as belonging to A. occidentalis .

Variation. Some females exhibit the SGP with the lateral lobes right-angled. Sometimes, the posterolateral corners are slightly pointed. Also, females can present an asymmetrical SGP, with a slightly smaller lateral lobe on the right margin. Additionally, the commonly tilted-to-the-right left endosomal sclerite in the phallosoma of the males can be mesally directed and perpendicular to the right sclerite.

Type locality. United States of America: Arizona: Cochise County .

La Rivers (1951: 324) originally reported the type locality as only Cochise County and stated: “no specific locality is given on the collecting labels, but since this is the largest and most representative series available, and Cochise County is not a very large area, no real problems are likely to result from this omission.” On the next page of the same work, in the Material examined section, La Rivers (1951: 325) reported the specific location “San Bernardino Ranch ( 3,750 ft)” as the type locality of A. occidentalis . This was most likely because San Bernardino Ranch was the sole specific locality on data labels of specimens from Cochise County in the type series.

Repository. Male holotype ( Fig. 21A ) is housed at the SEMC.

Published records: MEXICO: Baja California, Sinaloa, Sonora; UNITED STATES: Arizona, California ( La Rivers 1951, 1958; Davis 1986; Reynoso-Velasco & Sites 2019b). The record from Sinaloa ( Davis 1986) was based on a single male from the southern part of the state, which was not examined during this study. The southern location (east of Concordia) of this record and the current concept of the species suggests this specimen could belong to A. hydor , which is commonly found throughout Sinaloa; thus, further examination of the specimen is necessary to clarify its identity. This record is not included in the distribution map.

New record: Mexico: Chihuahua.

Distribution. Ambrysus occidentalis is distributed in extreme northwestern Mexico and southwestern United States ( Fig. 22 ) at elevations below 1,800 meters. In Mexico, the species is present in at least four biogeographic provinces: Baja California (in the homonymous state), northernmost section of the Pacific Lowlands ( Sinaloa, Sonora) and Sierra Madre Occidental ( Chihuahua, Sonora), and the northwesternmost section of the Chihuahuan Desert ( Chihuahua). In the United States, A. occidentalis is distributed southwest of the Colorado Plateau, in at least three other physiographic provinces: southwestern section of the Basin and Range ( Arizona, California), southernmost section of the Pacific Border ( California), and the small area of the Lower California province ( California). The arched distribution pattern of the species, with scarcely any records in the area encompassing western Sonora and northeastern Baja California in Mexico and southeastern Arizona and southwestern California in the United States, is most probably due to the dry conditions present in the Sonoran Desert.

Type material examined. HOLOTYPE ♂ (by original designation). UNITED STATES: Arizona: Cochise Co., 29-VII-1927, P.A. Readio [ R. H. Beamer was reported in the original description] / Ambrysus occidentalis La Rivers HOLOTYPE / Ambrysus occidentalis La Rivers determined by Ira La Rivers 1948 . PARATYPES: same data as holotype but R. H. Beamer coll. ( 2♂, 2♀ SEMC) . California: [ San Diego Co.], Miramar , 28-VII-[19]38, R. I. Sailer coll. / Ambrysus occidentalis La Rivers Paratype ( 1♀ UMC). MEXICO: Sonora: Álamos, Palmer District , 27-X-1934, H.S. Gentry / Ambrysus occidentalis La Rivers Paratype ( 1♀ SEMC) .

Additional material examined. MEXICO: Baja California: Ensenada Lake, 19-VII-[19]24, W. Benedict / Ambrysus occidentalis La Rivers Paratype ( 1♂ UMC) [an unpublished paratype]; [Mpio. Ensenada], [del] Tajo Canyon, 25–27-X-1955, C.F. Harbison coll. / Ambrysus vanduzeei Usinger 1946 (Ira La Rivers) / Ira La Rivers Collection bequeathed to the California Academy of Sciences - 1978 ( 1♂ CAS); [Mpio. Ensenada], 20 mi S of Santo Tomás, 03-VIII-[19]38 / Ross & Michelbacher colls. ( 4♂, 3♀ CAS); [Mpio. Mexicali], Guadalupe Canyon,, 18-V-1957, F.X. Williams coll. ( 1♂ CAS); same but / Cal. Acad. / Ambrysus ( 1♂ CAS); [Mpio. Mexicali], Guadalupe Canyon, Sierra Juárez, 06-VIII-1955 / R. Orr & C. Tosa colls. ( 1♂ CAS); same but 21-VI-1988, Bauman, Kirschner, Kondratieff, Wells & Whiting colls. ( 1♀ BYU); [Mpio. Mexicali], Guadalupe C[a]n[yon], S[ierr]a Juárez, / 01-XI-1967, J.A. Gruwell coll. / California State Univ., Long Beach 1996 donation to Calif. Acad. Sci. ( 1♀ CAS); same but N. 59 / E.L. Sleeper coll. ( 1♂, 2♀ CAS). Chihuahua: [Mpio. Ahumada], Ojo Carbonera Spring on SW side of Ejido Rancho Nuevo, 06-VI-1979, M.L.Smith & B. Chernoff colls. BC79-23/ Ambrysus sp. ( Hemiptera : Naucoridae ) ( 2♀ UMMZ); [Mpio. Casas Grandes], Ojo Barileño [Vareleño] 8 mi W of Nuevo Casas Grandes, 02-V-1978, R. R. Miller et al. colls, M-78-45, Ambrysus Stål Naucoridae det. E. Bright June 2003 ( 1♂, 1♀ UMMZ); [Mpio. Janos], Ojo Caliente NW of Yanos [Janos], 29-V-1978, Miller, Marsh & Smith, M78-14 ( 7♂, 4♀ UMMZ); [Mpio. Temósachi], Río Yepachic [at Yepachic, 5700’], CL2324, 22-IV-1988, J. T. & D.A. Polhemus colls. ( 1♂ USNM). Sinaloa: [Mpio. Choix], Río Chinipas (Río La Plata) 21 mi NE Aqua Calienta [Agua Caliente], 20-II-1957, Miller coll. ( 1♀ UMMZ); [Mpio. Choix], Choix, Río Choix, CL1643, 24-IV-1981, J. T. & D.A. Polhemus colls. / C.J. Drake Accession ( 2♀ USNM); [Mpio. El Fuerte, El] Fuerte, I-2001, B. Heaton coll. ( 1♂, 1♀ BYU). Sonora: Mpio. Álamos, Arroyo La Vinatería at Taymuco (El Vado), 27°14’39.7’’N, 108°43’17.3’’W, 537 m, L-1683, 25-XII-2013, Reynoso-Velasco, D. coll. ( 1♂, 4♀); Mpio Álamos, Rancho Acosta, 11-IX-1979, aquatic light trap / D.W. Moss, C.Y. Kitayama & G.W. Ulrich colls. ( 3♂, 3♀ EMEC): Mpio. Álamos, Río Mayo at Nahuibampo, 27°22’28.8’’N, 108°54’34.4’’W, 158 m, L-1685, 26-XII-2013, Reynoso-Velasco, D. coll. ( 6♂, 4♀ UMC); [Mpio. Álamos], Upper Río Mayo [NW of San Bernardo, above Presa Bicentenario Los Pilares], CL1636, 19-IV-1981, J. T. & D.A. Polhemus colls. / C.J. Drake Accession ( 2♂, 3♀ USNM); same but / Ambrysus sonorensis 1981 Usinger J. T. Polhemus ( 1♂ USNM); [Mpio. Nacozari], Rancho de Los Baños, CL108, 03-VI-1975, J. T. Polhemus coll. / taken at night / C.J. Drake Accession ( 1♀ USNM); [Mpio. Nacozari], Rancho de Los Baños, CL2316, 18-IV-1988, J. T. & D.A. Polhemus colls. ( 15♂, 4♀ USNM); same but 30 mi NE of Nacozari ( 2♂, 3♀ USNM); [Mpio. Navojoa], 1 mi SW Navojoa, 27-VI-1962 / E.L. Sleeper cool. / California State Univ., Long Beach 1996 donation to Calif. Acad. Sci. ( 2♂, 4♀ CAS); [Mpio. Yécora], [Arroyo Milpillas at] Tepoca [on Hwy 16], [1800’], CL2317, 20-IV-1988, J. T. & D.A. Polhemus colls. ( 1♂, 3♀ USNM); [Mpio. Yécora], [spring in] rock tank 3 mi W of Yecora, [5100’], 20-IV-1988, CL2319, D.A. & J. T. Polhemus colls. ( 1♂, 2♀ USNM); [Mpio. Yécora], 1 mi E Maicoba, 26-IV-1982, D.A. & J. T. Polhemus colls. / C.J. Drake Accession ( 15♂, 12♀ USNM); same but / Ambrysus occidentalis La Rivers det. J. T.P. ( 1♂ USNM); [Mpio. Yécora], 1 mi W Yécora, 26-IV-1982 D.A. & J. T Polhemus / C.J. Drake Accession ( 5♂, 4♀ USNM); same but / Ambrysus occidentalis La Rivers det. J. T. Polhemus ( 1♀ USNM); [Mpio. Yécora], 11 mi E [of] Yécora, 26-IV-1982, D.A. & J. T Polhemus / C.J. Drake Accession ( 6♂, 5♀ USNM); [Mpio. Yécora], 19 mi NE Yécora, 26-IV-1982, D.A. & J. T Polhemus / C.J. Drake Accession ( 1♂, 1♀ USNM); [Mpio. Yécora], 12 mi E of Maicoba, [4800’], CL2323, 22-IV-1988, J. T. & D.A. Polhemus colls. ( 6♂, 5♀ USNM); stream pools 20 SE Esqueda, 26-VI-1168 [1968], F.N. Young coll. ( 1♀ UMC). UNITED STATES: Arizona: [Cochise Co.], Benson, 25-III-1933, Bryant coll. / Ambrysus occidentalis ‘70 La Rivers det. J. T. Polhemus / C.J. Drake Accession ( 1♂ USNM); [Cochise Co.], Douglas, 30-IV-1935, W.W. Jones / Presented by W.E. Jones / Ambrysus signoreti Stål det. R.I. Sailer ( 1♀ EMEC); Cochise Co., [F.H.] Snow coll. / Van Duzee Collct’n Acc. 4943 / A. signoreti det. V.D., Carnegie Museum ( 1♀ CMNH); Cochise Co., San Bernardino Ranch, 3750 ft, VIII-[no year], F.H. Snow coll. ( 1♂ UMC); same but Ambrysus occidentalis Usinger (sic) det. Hungerford ( 1♀ UMC); Cochise Co., 02-IX-1991, Coll. Loc. 2543, J. T. Polhemus coll. / Bear Cr., 6.5 mi W Coronado N.M. / C.J. Drake Accession ( 3♂, 4♀ USNM); same but / Topotype Ambrysus occidentalis La Rivers det. J. T. Polhemus ( 1♂ USNM); [Gila Co.], E[ast] Verde Riv[er], 7 mi N Payson, 11-IX-1958, A. Menke coll. / C.J. Drake Accession ( 3♂ USNM); same but / Ambrysus occidentalis La Rivers det. Menke ‘62 ( 1♀ USNM); Gila Co., East Verde River 7 mi N Payson, 11-IX-1958, Menke & Stange colls. / C.J. Drake Accession ( 1♂, 2♀ USNM); same but / Ambrysus occidentalis La Rivers ( 1♀ USNM); [Gila Co.], Tonto Creek, 20-IV-1904, F.M. Chamberlain coll. ( 1♀ USNM); same but 5.4 mi SE of Jakes Corner off Hwy 188, 01-IX-1990, D.P. Herman coll. ( 2♀ UMC); same but 1–2-IX-1990, J.A. Back ( 1♂, 1♀ UMC); same but 20-XI-1990, aquatic vegetation/algae ( 1♂ UMC); Gila Co., 5 mi SE Jake’s Corner, 18-IV-1982, D.A. & J. T Polhemus colls. / C.J. Drake Accession ( 1♀ USNM); Maricopa Co., Fish Creek E of Tortilla Flat, [upstream from bridge] along Hwy Arz. 88, 03-XII-1980, J. T. Polhemus coll. / CL1624 ( 2♂, 1♀ USNM); Maricopa Co., Hassayampa [River] 5 mi S of Wickenburg, 26-XI-1984, D.A. Polhemus coll. ( 1♀ USNM); Maricopa Co., Salt River, 33°33’27’’N, 111°36’28’’W, elev. 1350 ft, 09-VIII-2021, rocks & algae, R.W. Sites, L-2097 ( 5♂, 10♀ UMC); [Maricopa Co., Seven Springs Recreational Area] N of Carefree, 18-I-1972, CL542, J. T. Polhemus coll. / seven springs / C.J. Drake Accession ( 5♀ USNM); Maricopa Co., 10-VII-1985, Jaime García coll. ( 1♂ UMC); Mojave Co., Burro Creek at Hwy 93, 15-IV-1988, D.A. & J. T. Polhemus colls. ( 2♂, 4♀ USNM); Pima Co., Sabino C[a]n[yon], [Santa] Catalina Mts. , 25-IX-1957 ( 1♂ USNM); same but 10-II-1957 / C.W. O’Brien coll. ( 1♂ USNM); Pima Co., Tanque Verde Cnyn nr. Tucson, 06-XI-1988, R. Rathman coll. ( 2♂ UMC); Santa Cruz Co., pond on Ruby Rd nr. c[a]mpgr[oun]d at Peña Blanca lake, 10-IV-2011, G. Challet coll. ( 1♂, 1♀ UMC); Yavapai Co., Santa Maria River, 15-IV-1988. D.A. & J. T. Polhemus colls. ( 9♂, 3♀ USNM); [Yavapai Co.], 5 mi NE of Castle Hot Springs, CL312, 07-X-1964, J. T. Polhemus coll. / C.J. Drake Accession ( 3♂, 2♀ USNM); same but / Ambrysus occidentalis La Rivers det. J. T. Polhemus ( 1♂ USNM); [Yuma Co.], Yuma, 07-IV- 1879, 150 ft. / Andreas Bolter Collection / INHS Insect Collection 461,358 ( 1♀ INHS); [no specific locality], Arizona, [F.H.] Snow coll. / 1348 / Carnegie Museum ( 1♀ CMNH). California: [Los Angeles Co.], Pasadena, / from Geo. Frank / H.G. Barber coll. 1950 / L. signoreti Mont. det. Montandon / C.J. Drake Accession ( 1♂ USNM); Los Angeles Co., Santa Ana Canyon / Green River, 17-X-1937, Grace O. Wiley coll. / J.C. Lutz Collection 1961 ( 1♂ UMC); [Orange Co.], Modjeska Reservoir / 12-II-30, Norland / Limnocoris portheo? La Rives 1979 det. J. T. Polhemus / C.J. Drake Accession ( 1♀ USNM); Orange Co., San Juan Canyon, 16-VII-1979, CL15, C.N. McKinnon coll. / Ambrysus occicentalis LaR det. C.N. McKinnon ‘80 / C.J. Drake Accession ( 1♂ USNM); [Orange Co.], San Juan Capistrano, jct. San Juan Ck. & San Diego Hwy., 24-XII-1976, C.N. McKinnon coll. / Ambrysus occicentalis LaR det. C.N. McKinnon ‘77 / C.J. Drake Accession ( 1♂ USNM); Orange Co., San Juan Creek, Hwy 74, [near San Juan Capistrano], CL1621, 09-XII-1979, J. T. Polhemus coll. ( 1♂, 1♀ UMC); same but / C.J. Drake Accession ( 7♂, 8♀ USNM); same but / Ambrysus occidentalis La Rivers det. J. T Polhemus ( 1♂ USNM); Riverside Co., Corona, 9-14-1958 / M.E. Irwin coll. / C.J. Drake Accession ( 1♂, 1♀ USNM); Riverside Co., Santa Rosa Mts., Magnesia Springs Can[yon], 11-XII-1980, 500’–1200’, D. Giuliani coll. ( 1♀ CSCA); San Bernardino Co., Afton Canyon, Mojave River, 01-I-1956, Menke & Stange colls. / C.J. Drake Accession ( 2♂, 1♀ USNM); same but / Ambrysus occidentalis La Riv. det. Menke ( 1♀ USNM); [San Bernardino Co.], Hot Springs, 09-VIII-1922 / Ambrysus signoretii (sic) Stål / L. Eyrand coll. ( 1♀ UMC); [San Bernardino Co.], Zzyzx Springs, 13-IV-1968, CL422, J. T. Polhemus coll. / C.J. Drake Accession ( 3♀ USNM); same but / Ambrysus occidentalis La Riv. det. J. T. Polhemus ( 1♀ USNM); San Diego Co., San Mateo Creek at Interstate 5, 13-VII-1984 / J.P. Webb coll. ( 1♂, 1♀ UMC).

Figures

FIGURE 20. Structures of Ambrysus occidentalis La Rivers. (A) Dorsal habitus of female, (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).

FIGURE 21. Ambrysus occidentalis La Rivers. (A) Dorsal habitus, labels, and dissected last abdominal segments of male holotype, (B) subgenital plate and labels of female paratype (allotype).

FIGURE 22. Distribution of Ambrysus occidentalis La Rivers.