Veromessor lariversi, Smith, 1951

Johnson, Robert A., Borowiec, Marek L., Snelling, Roy R. & Cole, Arthur C., 2022, A taxonomic revision and a review of the biology of the North American seed-harvester ant genus Veromessor (Hymenoptera: Formicidae: Myrmicinae), Zootaxa 5206 (1), pp. 1-115 : 52-61

Veromessor lariversi

( Figures 1E , 28 , 29A–C , 31–32 )

Distribution— Figure 27B

Veromessor lariversi Smith, 1951: 94 (worker). Types examined: holotype worker [USNM: USNMENT00529582], #61266, 6 paratype workers [LACM], 5 paratype workers [MCZC], 13 paratype workers [USNM], UNITED STATES, Nevada: Washoe County, Nevada Dominion Mine, Pyramid Mining District, Mullen Gap at 5 miles west of Pyramid Lake (Ira La Rivers, 8 May 1951); Cole, 1955: 52 (queen).

Messor lariversi (Smith) ; Bolton 1982: 341 (first combination in Messor ).

Veromessor lariversi Smith ; Ward, Brady, Fisher, and Schultz, 2015: 13 (revived combination in Veromessor ).

Worker diagnosis. This species is uniquely characterized by the following combination of features: (1) light yellowish to yellowish-orange or yellowish-red, gaster sometimes slightly darker, (2) medial lobe of clypeus arugose, smooth and shining, not thick and protuberant in profile, not elevated above lateral lobes in frontal view, (3) mandibles with 7, or rarely 8 teeth, (4) dorsal base of scape not flattened, slightly widened; maximum basal width of scape less than maximum preapical width, (5) MOD distinctly greater then OMD, OI> 28.0, (6) cephalic dorsum with few discontinuous, medial, longitudinal rugae that weaken laterally and disappear posterior to eyes, posterior margin smooth and shining, rugae more coarse and well-defined in front of and below eyes, dorsum mostly smooth and shining with scattered pilgerous punctures, (7) psammophore well developed; ventral surface of head capsule with many long J-shaped hairs arranged in a distinct row around the outer margin of the ventral region of the head capsule, (8) dorsum and sides of pronotum weakly roughened and shining or weakly to strongly coriarious to lineogranulate, weakly shining; mesonotum with piligerous punctures to moderately punctulategranulate, weakly shining to shining; mesopleura variable: faintly to strongly lineogranulate or strongly granulate between few, irregular longitudinal rugae or faintly granulate between longitudinal rugae dorsally and moderately to strongly granulate and arugose ventrally, (9) sides of propodeum weakly punctate-granulate between longitudinal or oblique rugae or lineogranulate; propodeal spines divergent, triangular, acuminate, length similar to width at base; length less than distance between their bases and length <0.5× MOD; infraspinal facet and propodeal declivity micropunctate, shining, and (10) metasternal process higher than long, apex subangulate. Additional diagnostic characters that separate V. lariversi from V. pseudolariversi are: (1) in profile, the anteroventral margin of the postpetiole is continuous, lacking a minute process, and (2) relatively smaller eye with fewer ommatidia ( Figures 28 , 29A–C , 30 ).

Measurements. holotype (n = 25 + 10 paratypes). HL 1.31 (1.06–1.42); HW 1.23 (0.93–1.37); MOD 0.39 (0.33–0.43); OMD 0.32 (0.26–0.38); SL 1.17 (0.87–1.27); PNW 0.81 (0.59–0.98); HFL 1.48 (0.95–1.62); ML 1.75 (1.29–1.93); PW 0.23 (0.16–0.26); PPW 0.40 (0.29–0.45). Indices: SI 95.12 (80.56–107.53); CI 93.89 (83.041– 104.00); OI 31.71 (28.57–38.38); HFI 120.33 (87.96–129.90).

Queen diagnosis. This caste is diagnosed by the following combination of features: (1) head and mesosoma dark orangish-brown to dark brownish-orange; gaster slightly lighter orangish-brown, (2) medial lobe of clypeus not thick and protuberant in profile, not elevated above lateral lobes in frontal view, medial lobe mostly smooth and arugose with numerous micropunctures, (3) mandibles with 7 teeth, (4) dorsal base of scape slightly flattened, but not widened; maximum basal width of scape less than maximum preapical width, (5) MOD distinctly greater than OMD, (6) cephalic dorsum with prominent longitudinal rugae medially, around eyes, and on malar area; rugae faint to lacking between medial rugae and eyes; rugae lacking posterior to ocelli, posterior margin smooth and shining, (7) psammophore well developed, (8) sides of pronotum moderately granulate between fine longitudinal rugae; mesoscutum and mesoscutellum smooth and weakly shining with scattered piligerous punctures; anepisternum moderately shining between fine, longitudinal rugae; katepisternum largely smooth and shining with longitudinal rugae near anterior and posterior margins, (9) propodeum moderately coriarious between longitudinal and oblique rugae; propodeal spines triangular, about as long as width as base, apex bluntly rounded, length less than the distance between their bases; infraspinal facet and propodeal declivity smooth and weakly shining, and (10) metasternal process higher than long, apex rounded. An additional diagnostic character is that in profile, the anteroventral margin of the postpetiole is continuous, lacking a minute process ( Figure 31 ).

Measurements. (n = 4). HL 1.55–1.61; HW 1.53–1.62; MOD 0.43–0.54; OMD 0.36–0.43; SL 1.29–1.39; HFL 1.78–1.84; ML 2.78–2.98; PW 0.40–0.44; PPW 0.63–0.74. Indices: SI 79.63–88.54; CI 95.03–101.94; OI 27.22–34.39; HFI 109.88–119.61.

Male diagnosis. This caste is diagnosed by the following combination of features: (11) head dark brownish, rest of body light orangish-brown, (12) clypeus weakly convex, anterior margin nearly straight across middle, (13) mandibles with 3 or 4 small teeth or denticles basad of apical tooth, (14) anterior ocellus well above level of tops of eyes, (15) anepisternum mostly smooth and shining with numerous weak punctures; katepisternum mostly smooth and shining, (16) propodeum lacking denticles, with few widely spaced longitudinal rugae, especially laterad, (17) metasternal process prominent, triangular, acuminate, and (18) subpetiolar process digitiform with lamella tapering posterad ( Figures 1E , 32 ).

Measurements. (n = 1). HL 0.81; HW 0.72; MOD 0.40; SL 0.35; HFL 1.66; ML 1.99; PW 0.30; PPW 0.43; AOD 0.12; IOD 0.25; OOD 0.23. Indices: SI 48.61; CI 88.89; OI 55.56; HFI 230.56.

Additional material examined. UNITED STATES: California: Inyo Co. : Eureka Valley , Mar 1978 ( LACM) ; Deep Springs, Sep 28, 1978 ( LACM) . Lassen Co.: 1.5 km NE Wendel , 1250 m, Jul 6, 2008 ( UCDC) ; 13 km at 9.5 o N Doyle , 1240 m, Jun 27, 2004 ( UCDC) ; 5.3 mi NE Litchfield , 4200’, Jul 24, 1969 ( LACM) . Los Angeles Co.: Saddle Back Butte, 3020’, Apr 28, 1998 ( LACM) . San Bernardino Co.: China Lake at Paxton Dunes at 13 mi NNE Ridgecrest, 2200’, Apr 13–29, 1982 ( UCDC) . Nevada: Churchill Co.: Sand Mountain, T 17N, R32E, 4200’, Apr 22, 1979 ( LACM) ; Sand Mountain at 25 mi SE Fallon, Mar 18–Aug 1, 1980 ( UCDC) ; Blow Sand Mtns (T15N, R30E), 4500’, Jun 29, 1979 ( LACM) ; 16 mi N Fallon , 3500’, Jun 8, 1971 ( LACM) ; 28 mi N Fallon , 4000’, Jun 8, 1971 ( LACM) ; Sand Spring Dune , 1200 m, Jun 30–Jul 2, 1996 & Aug 2, 1996 & Jun 5, 2000 & Jul 3, 2008 & Jul 3, 2012 ( CASC; MCZC; MLBC; UCDC) . Esmeralda Co.: Hwy 266 at 0.1 mi N California state line, 4980’, Jul 22, 1992 ( RAJC) . Humboldt Co.: 10 mi NNE Winnemucca (T37N, R38E, Sect 9), 4400’, Jun 24, 1971 ( LACM) . Lander Co.: Big Smoky Valley, T 10N, R43E, Sect 17, 5900’, May 3, 1971 ( LACM) . Lyon Co.: Silver Springs Junction, Jun 28–29, 1954 ( LACM; MCZC) ; 2 mi ESE Silver Springs , 4000’, Jul 18–20, 1973 ( LACM; MCZC; RAJC) ; Smith , Sep 13, 1953 ( LACM) ; 3 mi E Smith , May 23, 1971 ( LACM; RAJC) ; 6 km E Weeks , 1280 m, Jun 28, 1998 ( UCDC) ; 0.2 mi NW Jct Hwy 477 & I-80, 4120’, Jul 24, 2018 ( RAJC) ; Fort Churchill State Historic Park , 1285 m, Jul 1, 2010 & Jul 2, 2012 & Jul 1, 2014 & Jun 29, 2016 & Jul 27, 2018 ( MLBC; MMPC; RAJC; UCDC) ; Hwy 95 at 6.9 mi E Jct Hwy 208, 4400’, Jul 28, 2018 ( NHMW; RAJC) . Mineral Co.: Schurz, 4250’ May 3, 1965 ( LACM; MCZC) ; T14 N, R33E, Sect 11, 5800’, May 17, 1971 ( LACM) ; 1.4 mi SE Jct Hwys 95 & 360, 4350’, Jul 10, 2019 ( RAJC) . Nye Co.: Round Mountain , 5900’, Jul 15, 1954 ( LACM) ; Cactus Range, May 12, 1953 ( LACM) ; Big Dunes at 10 mi W Lathrop Wells , 2600’, May 1, 1970 ( LACM; RAJC) ; Nevada Test Site, near Mercury, Jun 1962 ( USNM) ; Hot Creek Valley at Moore’s Station (T7N, R51E), 7000’, Aug 21, 1969 ( LACM) ; Hwy 95 at 16.3 mi SE Scotty’s Junction , 3980’, Jul 10, 2019 ( RAJC) . Washoe Co.: Wadsworth , Jun 30, 1971 ( LACM) ; 1.7 mi NW Wadsworth , 4000’, Sep 10–11, 1975 ( LACM) ; 2.8 mi W Wadsworth , May 30, 1963 & May 26, 1965 & Jun 21, 1968 ( LACM) ; 3 mi W Wadsworth , Nov 21, 1968 ( LACM) ; 4 km WSW Wadsworth , 1270 m, Jun 30, 2002 ( UCDC) ; 24 mi S Gerlach , 3900’, Jun 11, 1971 ( MCZC) ; 21 mi N Gerlach , 4100’, Jun 15, 1971 ( LACM; RAJC) ; 18 mi S Gerlach , 4500’, Jun 11, 1971 ( LACM) ; 5 km S Nixon , 1185 m, Jul 8, 1982 ( UCDC) ; 10 mi N Nixon , 4000’, Jun 11, 1971 ( LACM) ; S end Pyramid Lake , 1140 m, Jul 6, 1990 ( MCZC; UCDC) ; T23 N, R20E, Sect 19, 5000’, May 12, 1974 ( LACM) ( Figure 27B ).

Etymology. This species was named after Ira La Rivers, biologist at University of Nevada, Reno, who collected the type series.

Discussion. Smith (1951) described V. lariversi from a holotype and 37 paratype workers; the holotype and 25 paratypes were deposited at USNM. All USNM specimens have the type labels USNM 61266 [listed as 61265 in Smith (1951)], but none of these specimens had a holotype label. All but one pin had a USNM 61266 PARATYPE label; the one exception was a pin with PARA crossed out. This pin also had a black dot on the triangle, and this specimen was presumed to be the holotype. Consequently, we placed a holotype label on this specimen.

Numerous series were subsequently collected by M. R. Smith, A. C. Cole, and R. R. Snelling that were all identified as V. lariversi until morphological variation in these series was conveyed to us by Phil Ward. Subsequent examination revealed that many of these series consisted of a species morphologically distinct from, but closely related to V. lariversi . Morphological differences that separate the two species include that workers of V. lariversi : (1) in profile, ventral margin of postpetiole continuous, lacking a minute process ( Figure 29A ), (2) in dorsal view and in profile, the pronotum and mesonotum arugose, weakly to strongly coriarious to punctulate-granulate ( Figure 29B–C ), and (3) a relatively smaller eye with fewer facets ( Figure 30 ). For workers of V. pseudolariversi : (1) in profile, anteroventral margin of postpetiole discontinuous with margin interrupted by a minute process, margin concave anterior to process ( Figure 29D ), (2) in dorsal view and in profile, the pronotum with discontinuous to continuous, irregular to irregular, transverse rugae; dorsum of mesonotum with one to few weak, irregular, usually discontinuous, longitudinal rugae ( Figure 29E–F ), and (3) a relatively larger eye with more facets ( Figure 30 ). Queens of the two species also differ in size. Worker allometry is similar for both species, but queens of V. pseudolariversi are distinctly smaller than those of V. lariversi and their males are larger ( Figure 33 ), in addition to other morphological traits given in the key to queens. A molecular phylogeny based on UCEs shows that these two lineages are sister, reciprocally monophyletic, and quite divergent. This phylogeny included specimens from Fort Churchill State Historic Park in Lyon County, Nevada, where both lineages occur sympatrically (M.L. Borowiec, unpub. data).

Cole (1955) described the queen of V. lariversi (Cole Coll. No. NEV-352), but no queens from this series were present in loans that we examined. However, eight workers from the NEV-352 series were examined and identified as V. lariversi , verifying that this description was of V. lariversi . Cole (1963) later redescribed the queen and described the male from Cole Coll. No. NEV-784. Unfortunately, no individuals from the NEV-784 series were available in our loans to verify this identification. It seems probable that this series was actually V. pseudolariversi given the much smaller size of the queen (6.59–6.72 mm in length) compared to the 9.4 mm length indicated in his earlier description of the V. lariversi queen ( Cole, 1955). That this description is that of V. pseudolariversi is also supported in that Figure 3B of Cole (1963) shows a small process on the anteroventral margin of the postpetiole of the male. Cole also described the male as rather uniformly black, which better fits the description for the male of V. pseudolariversi (see Figure 44 ) compared to the light brownish male of V. lariversi ( Figure 32 ). Other morphological characters were described too briefly to further verify this presumption.

Veromessor lariversi is broadly sympatric with several congeners including V. smithi , V. lobognathus , and V. pseudolariversi . This species is easily separated from all congeners except for the very similar V. pseudolariversi (see above). Workers of Veromessor lariversi are separated from V. smithi by: (1) smaller size (HW = 0.93–1.37 mm), (2) body concolorous light yellowish to yellowish-orange or yellowish-red, gaster often slightly darker, (3) maximum basal width of scape less than maximum preapical width, and (4) mandibles with 7 teeth. For V. smithi : (1) larger size (HW = 1.33–1.61 mm), (2) concolorous orangish-brown to rust colored, (3) maximum basal width of scape greater than maximum preapical width, and (4) mandibles with 8 teeth.

Veromessor lariversi workers are separated from V. lobognathus based on: (1) smaller size (HW = 0.93–1.37 mm), (2) body concolorous light yellowish to yellowish-orange or yellowish-red, gaster often slightly darker, (3) dorsum of pronotum weakly to strongly punctulate-granulate to lineogranulate, usually arugose, (4) maximum basal width of scape less than maximum preapical width, and (5) mandibles with 7 teeth. In V. lobognathus : (1) larger in size (HW = 1.28–1.82 mm), (2) light to dark orangish-brown to reddish-brown head and mesosoma, (3) dorsum of pronotum with weakly to strongly irregular rugae and numerous secondary rugae to rugoreticulate, (4) maximum basal width of scape greater than maximum preapical width, and (5) mandibles with 8 teeth.

Biology. The biologies are probably similar for V. lariversi and V. pseudolariversi , but it is difficult to ascribe published information to one species or the other because series numbers were not referenced in papers, voucher series were not collected, or series were absent from loans that we examined. Papers that discuss biology of “ V. lariversi ” include Bennett (2000), Cole (1955; 1966), Creighton (1953), Smith (1951), Snelling and George (1979), and Wheeler and Wheeler (1986). The following information on biology includes only that which could be verified from examined series or field observations of V. lariversi .

Veromessor lariversi workers are solitary, nocturnal foragers (R.A. Johnson, pers. obs.). Nests are usually polydomous with craters up to 10–15 cm in diameter, but sometimes consist only of an entrance lacking a crater. Colonies reach up to about 1,000 workers ( Cole, 1955) and are presumably monogynous. Workers are mostly monomorphic. Snelling and George (1979) collected both V. lariversi and V. pseudolariversi in California, and they indicated that colonies appear to aestivate in summer months. It seems more likely that these authors observed inactive colonies given that both RAJ and MLB have observed V. lariversi foraging in June.

Gland chemistry has not been examined in V. lariversi . Neither has the pygidial gland been examined, but we expect that this species has a small pygidial gland reservoir and lacks a textured tergal cuticle, as does it sister species, V. pseudolariversi , and all other small-colony congeners (see Hölldobler et al., 2013).

Mating flights have not been observed, but dealate queens have been collected from May 26–Jun 29, indicating that mating flights occur during summer. Cole (1963) found two dealate queens in one excavated nest, but it is unclear if this record was for V. lariversi or V. pseudolariversi .

Veromessor lariversi is a mostly Great Basin Desert species with a few records from the Mohave Desert. This species appears to be most common in sandy soils at elevations from 785–2,120 m. There is also one record from Los Angeles County, California, which suggests that V. lariversi is more widespread than indicated by current collection records. This species occurs in the Great Basin shrub steppe, Mohave Desert, and Snake-Columbia shrub steppe ecoregions, as defined by Olson et al. (2001) ( Figure 27B ).

Figures

FIGURE 1. Photographs of the metasternal process on males of Veromessor: (A) V. andrei (CASENT4010823), (B) V. chamberlini (UCRC_ENT00500152), (C)V.chicoensis (CASENT0869853), (D) V.julianus (LACMENT359792),(E)V.lariversi (CASENT0761204), (F) V. lobognathus (LACMENT363986), (G) V. pergandei (CASENT0869850), (H) V. pseudolariversi (CASENT0869851), (I) V. smithi (LACMENT364071), and (J) V. stoddardi (LACMENT364102). Photographs by Robert Johnson from www.AntWeb.org.

FIGURE 3. Photograph of Veromessor andrei worker (red form): (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0923139). Photographs by Wade Lee from www.AntWeb.org.

FIGURE 27. Geographic distribution of: (A) Veromessor julianus, (B) V. lariversi, and (C) V. lobognathus. The larger black circle in each panel denotes the type locality.

FIGURE 28. Photograph of Veromessor lariversi worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0923148). Photographs by Wade Lee from www.AntWeb.org.

FIGURE 29. Photographs of diagnostic characters to distinguish between workers of Veromessor lariversi Smith and (A–C) V. pseudolariversi (D–F).Photographs of V. lariversi worker (CASENT0923148): (A) anteroventral margin of postpetiole lacking a minute process, margin with a continuous profile, and (B) in profile and (C) in dorsal view, pronotum and mesonotum arugose and weakly to strongly coriarious to punctulate-granulate. Photographs of V. pseudolariversi paratype worker (CASENT0923121): (D) anteroventral margin of postpetiole with a minute process that interrupts the continuous profile, margin weakly concave anterior to process, and (E) in profile and (F) in dorsal view, pronotum with discontinuous to continuous, wavy to irregular transverse rugae; dorsum of mesonotum with one to few weak, wavy to irregular, usually discontinuous longitudinal rugae. Photographs by Michele Esposito and Wade Lee from www.AntWeb.org.

FIGURE 30. Bivariate plots for workers of V. lariversi and V. pseudolariversi: (A) mesosoma length versus number of eye facets, and (B) mesosoma length versus eye length. Sample size for each species is in parentheses.

FIGURE 31. Photograph of Veromessor lariversi dealate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (LACMENT363890). Photographs by Wade Lee from www.AntWeb.org.

FIGURE 32. Photograph of Veromessor lariversi male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0761204). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 33. Bivariate plots for workers, queens, and males of Veromessor lariversi and V. pseudolariversi: (A) head width versus head length and (B) head width versus mesosoma length. Sample size for each caste is in parentheses.

FIGURE 44. Photograph of Veromessor pseudolariversi male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0869851). Photographs by Robert Johnson from www.AntWeb.org.