Polyphylla socorriana La Rue, 2016

La Rue, Delbert A., 2016, Natural history, ecology, and conservation of the genus Polyphylla Harris, 1841. 1. New species from the southwestern United States and Baja California, Mexico, with notes on distribution and synonymy (Coleoptera: Scarabaeidae: Melolonthinae), Insecta Mundi 2016 (491), pp. 1-41 : 14-18

Polyphylla socorriana La Rue , new species

( Fig. 20–27 , 56–57 )

Type material. Holotype. Male ( UNAM). Labeled “ MEXICO, Baja California, Highway 1, south of San Quintín, Socorro Sand Dunes, 10 m, 3.VII.1998, at blacklight, J.D. Beierl collector.” Allotype. Female ( UNAM). Labeled “ MEXICO, Baja California, Socorro Sand Dunes, north of San Quintin at 1 mi. W. Hwy. 1, 30’ el., 26.VIII.2002, R.A. Cunningham, G. Nogueira. ” Paratypes. (14). Labeled as holotype (4 males); as allotype except “MV” (5 males); “ MEXICO, Baja California, 1 mile N. El Socorro, 10 m, El Socorro Dunes , 2.VII.1996, R.A. Cunningham ” (1 male) ; “ MEXICO, Baja California, San Ramon , 4 mi W of Colonio Guerraro, 3.VII.1969, L.F. La Pré, UV light” (4 males). CASC, MXAL, RACC, RHMC, UCRC .

One additional male specimen excluded from the type series because of considerable dorsal abrasion and disparate locality: “ MEXICO, Baja California, 2.7 mi E. EJ [Ejido] Bonfil, Rio San Rafael, 27.VI.1986, Faulkner, Bloomfield”.

Description. Holotype. Male ( Fig. 20, 22, 24–26 ). Length 26.5 mm. Greatest width 12.5 mm. Humeral width 11.0 mm. Form. Elongate, robust, slightly ovate at basal 1/3. Color. Head, eyes, elytral humeri, protibial dentition black; pronotum, scutellum, pygidium, legs, abdominal sternites, pterothoracic integument, basal antennomeres, and other appendages of head rufotestaceous; elytra deep rufotestaceous; lamellate antennomeres light testaceous; except where noted, setal and squamal vestiture white. Head. Convex; clypeus transverse with reflexed bisinuate anterior margin; anterior angles obtuse, lateral margins sinuate, converging basally; disc depressed, coarsely punctate, densely setose with long pale setae and contiguous to imbricate acuminate scales. Frontoclypeal suture arcuate, variably obscured by coarse punctation. Frons feebly depressed medially, coarsely punctate with long, recumbent setae, and solitary, acuminate scales. Vertex medially tumid and glabrous. Maxillary palpomere-4 cylindrical, anteriorly depressed, distally truncate; finely punctate and variably setose; 2/3 length of three basal palpomeres combined. Mentum transverse, anteriorly emarginate, angles rounded, disc slightly concave, with scattered setae and solitary scales. Antennae. Scape bulbous, constricted basally, provided with a dense, scopula of long setae; lamellate antennomeres 4–10 distally recurved obtusely outward, provided with randomly distributed setae. Antennal club 2.2× (linear measurement) or 3.2× (curvilinear measurement) longer than basal antennomeres combined. Pronotum. Broadly convex, transverse, 2× wider than length at midline, widest at posterior 1/2; anterior angles obtuse, basal angles broadly arcuate and explanate; marginal bead absent anteriorly, coarsely serrate laterally, feebly indicated to evanescent posteriorly. Disc moderately to coarsely punctate, an acuminate scale arising from each puncture, medially with long, suberect to recumbent setae; medially sulcate, dividing a transverse tumidity at posterior 1/2; trivittate; medial vitta longitudinally complete, submarginal vittae eroded at apical 1/3, basally with two distinct glomerate patches of dense, imbricate, acuminate scales and solitary setae. Scutellum. Oblong, broadly rounded, margins glabrous, disc coarsely punctate, provided with contiguous to imbricate scales and suberect setae. Elytra. 2.5× greater in length than width; humeral and posterolateral angles broadly arcuate. Marginal bead reflexed, explanate anteriorly, evanescent posterolaterally, sutural bead obscured by dense acuminate scales. Disc shallowly punctate; calli tumose, glabrous, sparsely punctate; vestiture composed of contiguous acuminate scales and solitary, suberect setae; distinctly vittate; vittae longitudinally continuous with edges eroded, composed of dense imbricate, acuminate scales obscuring integument; each with a parallel, glabrous band on either side; discal and subsutural vittae adjoined basally ( Fig. 26 ). Metathoracic wings functional. Pygidium. Subtriangular, convex, length subequal to width, angles obtusely rounded; disc finely punctate, depressed behind greatly reflexed margins; vestiture composed of contiguous to imbricate, acuminate scales and short, recumbent setae. Venter. Densely pubescent obscuring pterothorax; exposed abdominal sternites convex, with a basal glabrous band, depressed medially; vestiture composed of solitary, acuminate scales basally and solitary, pale yellow setae. Legs. Protibia strongly bidentate, basal third tooth feebly indicated as an obtuse angular projection; dentition widely separated, projecting perpendicular to longitudinal tibial axis; inner margin rounded, outer margin with a sharp, longitudinal carina; surfaces finely to coarsely punctate with solitary to contiguous, acuminate scales and scattered, pale yellow setae; meso-, metatibia with a dentiform projection and acuminate spines. All femora flattened, margins parallel, surface vestiture as protibiae. Apices of tarsomeres coronate with a fringe of translucent spiculae; tarsomere-5 elongate, less than length of basal tarsomeres combined, ventral surface bearing a fine carina extending length of tarsomere; tarsal claws with basal proximal tooth. Phallobase and parameres. Number examined (3). In dorsal aspect, symmetrical with two simple parameres narrowing distally, apices convergent; median notch sharply rounded, separated approximately 1/3 length of parameres; lateral aspect, apical 1/4 cristate with apices smoothly rounded ventrally; caudal aspect, subconvex, obliquely depressed; distal tips of parameres adjoined anterodorsally.

Allotype. Female ( Fig. 21, 23, 27 ). Length 23.0 mm. Greatest width 12.0 mm. Humeral width 10.0 mm. Excluding sexual dimorphic variation as holotype except: Form. Robust, subovate, widest at posterior 1/2. Head. Subconvex; clypeal disc shallow, devoid of setae; setal vestiture of lamellate antennomeres translucent golden yellow. Pronotum. Sharply convex; lateral marginal bead coarsely, deeply serrate; squamal vestiture pale yellow. Scutellum. Squamation evenly distributed. Pygidium. Triangular. Legs. Protibia strongly tridentate; dentition projecting obliquely forward from longitudinal tibial axis; tarsal claws with proximal tooth centrally positioned.

Variation. Males. (14). Length 22.0–27.0 mm. Greatest width 10.0–13.0 mm. As holotype except: Head. Clypeal squamae obscuring disc. Pronotum. Setal vestiture limited to discal margins (abrasion). Scutellum. With solitary pale setae. Legs. Protibial basal tooth variably developed.

Diagnosis. The prominent white dorsal vestiture and dense continuous elytral vittae of P. socorriana are similar to some disjunct psammophilous populations of P. decemlineata with heavy white dorsal squamation (= syn. P. comstockiana von Bloeker 1939 ). However, P. decemlineata lacks pronotal and elytral discal setae (present in P. socorriana ); has sharply defined, smooth-edged elytral vittae (uneven to eroded in P. socorriana ); yellowish-brown to black integument (deep rufotestaceous in P. socorriana ); and is a larger, robust species (length usually greater than 30 mm; type specimens of P. socorriana are between 22–27 mm).

Specimens of P. socorriana exhibiting an abraded dorsal vestiture may be confused with P. crinita which shares a proximal but allopatric distributional range ( Hardy 1981). That species has an olivaceous yellowish-brown to black integument (deep rufotestaceous in P. socorriana ); yellowish-brown interstitial squamae (white in P. socorriana ); and lacks the basally adjoined discal and subsutural elytral vittae. The presence or absence of pronotal discal setae is apparently variable in male P. crinita (present in P. socorriana ).

Although infrequent in some western clade species, the basally adjoined discal and subsutural elytral vittae of P. socorriana ( Fig. 26–27 ) is statistically stable and diagnostic. In addition to the types, twelve of fourteen paratypes (85%) exhibit this character.

The dorsal coloration of P. socorriana is presumably a selective response to the distinctive white sand color of the El Socorro Sand Dunes ecosystem and contiguous sand areas suggesting an adaptation toward parasematic crypsis.

Natural history. Based on field observations and specimen data, P. socorriana is a psammophilous obligate ecologically associated with coastal sand dunes. Males were attracted to black, ultraviolet, and mercury vapor light stations placed adjacent to, or a slight distance away from, the leeward side of the dunes shortly after twilight. The allotype female was encountered crawling on the sand surface at dusk (R.A. Cunningham, personal communication).

Locality data of the specimen excluded from the type series, “ 2.7 mi E. Ejido Bonfil, Rio San Rafael,” is slightly inland and ecologically dissimilar to that of the type series. This would suggest the possibility that P. socorriana may not be entirely restricted to a coastal ecosystem. However, the arenaceous substrates of Rio San Rafael, an ephemeral desert riparian wash that drains to the Pacific Ocean, are consistent with the psammophilous requisites of P. socorriana and may provide an ecologically suitable corridor for the species to disperse, albeit, marginally inland.

Ecology. El Socorro Sand Dunes ( Fig. 56–57 ) are located on the Pacific coast of the state of Baja California, Mexico, at an elevation of 10 to 45 m. Their pronounced white coloration is directly related to high carbonate content (aragonite and calcite) from skeletal marine invertebrates. High carbonate sand dunes are rare in North America occurring only along the Yucatan Peninsula, the Channel Islands of California, and Baja California ( Muhs et al. 2009).

The coastal strip from 32° to 29.5° north latitude, encompassing the type locality, has been documented to be an area of high floristic diversity with a conservation status of endemic (25%), sensitive (40%), or rare (35%) species (Johnson 1977; Riemann and Ezcurra 2005, 2007; Vanderplank 2010).

Adolphia californica S. Watson (california prickbush: Rhamnaceae ), Funastrum arenarium (Decaisne ex Bentham) Liede (talayote: Apocynaceae ), Heteromeles arbutifolia (Lindley) M. Roem (davis gold toyon: Rosaceae ), Rhamnus crocea insula (Kellogg) (buckthorn: Rhamnaceae ), and Yucca schidigera Roezl ex Ortega (splinter yucca: Agavaceae ) are found only on the El Socorro Dunes.

Abronia maritima Nuttall ex. S. Watson (red sand verbena: Nyctaginaceae ) is predominant on active dunes with A. umbellata Lamark (pink sand verbena: Nyctaginaceae ), Atriplex julacea S. Watson (saltbush: Amaranthceae), Eulobus californicus Torrey and A. Gray (california primrose: Onagraceae ), Funastrum arenarium Decaisne ex Bentham (climbing milkweed: Apocynaceae ), Helianthus niveus (showy sunflower: Compositae), and Heteromeles arbutifolia (Lindley) M. Roem (toyon: Rosaceae ) in stabilized dune areas ( Vanderplank 2010).

Ambient climate is classified as mediterranean (cool moist winters, hot dry summers) with average annual precipitation of approximately 13.5 cm and mean temperature of 17.5° C. The area experiences frequent moisture laden fog providing additional water resources and associated humidity which is critical in supporting the endemic species of the ecosystem ( Markham 1972; Delgadillo 1998).

Conservation. The unique high carbonate content, unusual floristic composition, high species diversity, and percentage of endemic taxa clearly indicate the El Socorro Sand Dunes a priority for conservation. The imminent threat to P. socorriana is habitat degradation. The entire dune system has been proposed for development to allow egress from Mexico Peninsular Highway 1. Other impending threats include trash dumping, recreational off-road vehicle use, invasive floristic species, and vegetation clearing ( Vanderplank 2010).

To underscore the negative impact of cumulative human encroachment and habitat modification of the region, the endemic tule shrew ( Sorex ornatus juncensis Nelson and Goldman : Soricida) is now extinct and the San Quintín kangaroo rat ( Dipodomys gravipes Huey : Heteromyidae ) is presumed ex- tirpated as no individuals have been found since the 1980s ( Best and Lackey 1985; Álvarez-Castañeda and Patton 1999).

Because of limited geographic range and imminent threat of extirpation from habitat modification, P. socorriana should be considered a “critically imperiled” species.

Remarks. Polyphylla socorriana is the second species of Polyphylla described from a coastal sand dune complex of the Baja California Peninsula. The other species is P. multimaculata Hardy (1981) from Dunas de Soledad, north of Guerrero Negro.

The Polyphylla fauna of the Baja California Peninsula now consists of seven species. Of these, five also occur in the southwestern United States ( P. cavifrons , P. crinita , P. decemlineata , P. nigra , P. rugosipennis Casey ), and two are endemic ( P. multimaculata , P. socorriana ).

Etymology. From a combination of “Socorro” and the Latin adjectival suffix, - iana, “belonging or related to.”

Common name. The El Socorro Sand Dunes polyphyllan scarab beetle.

Figures

Figures 20–27. Polyphylla socorriana. 20, 22, 24–26) Holotype male. 21, 23, 27) Allotype female.

Figures 50–57. Habitats. 50–51) Polyphylla anivallis. Animas Valley Sand Dunes, Hidalgo Co., NM. 52–53) Polyphylla koso. Coso Mountains, Inyo Co., CA. 52) Coso Bridge. 53) Mill Springs Canyon. 54–55) Polyphylla morroensis. Baywood Fine Sands, San Luis Obispo Co., CA. 56–57) Polyphylla socorriana. El Socorro Sand Dunes, Baja California, MX.