Schistocerca socorro ( Dirsh, 1974 ) Dirsh, 1974

Song, Hojun, 2006, Description of Schistocerca cohni n. sp. and redescription of S. socorro (Dirsh) (Orthoptera: Acrididae: Cyrtacanthacridinae) from Mexico, Zootaxa 1150, pp. 43-52 : 47-51

Schistocerca socorro ( Dirsh, 1974) n. stat. and just. emend.

( Figs. 2 A–2J, 3B)

Schistocerca americana socoro Dirsh, 1974: 59

Male. Medium size (total length = 49.95± 3.03 mm; hind femur length = 21.98± 1.80 mm; pronotum length = 8.83± 0.41 mm (n = 10)).

Antennae slightly longer than the combined length of head and pronotum. Integument highly setose. Setae on pronotum, sternum, abdomen and femora short. Median carina of pronotum distinct and slightly raised, and slightly constricted. Sulci distinct, but not deep. Dorsal surface of prozona sculpting pattern very finely granulous with faint ridges. Lateral lobes of prozona faintly papillulate and wrinkled. Hind angle of pronotum slightly obtuseangular. Granules absent. Pronotum width narrowing anteriorly. Tegmina extending beyond the tip of abdomen. Cerci slightly narrowing toward apex, with length about the same as width ( Fig. 2 J). Apical tip of cercus almost round, sometimes faintly bilobed, with upper and lower part forming elongated “3” shape. Furcula broad and sinuate, narrowing at the base. Epiproct with a pair of tubercle absent ( Fig. 2 H). Subgenital plate with smoothly angular and broad apex ( Fig. 2 I). Subgenital plate notch V­shaped.

Color: Overall dark brown. Dorsal stripe absent. Head brown with two subocular stripes, white anterior to dark brown. Two dark brown stripes converging on dorsal portion of head from behind eyes to occiput. Lateral lobes of pronoza with a faintly white horizontal streak. Marginal ridge of pronotum cream color. Epimeron brown without distinct marking. Tegmina semitransparent with distinct dark patches. Tegminal veins dark brown. Hind wings smoky. Posterior margin of abdominal tergites with a row of black dots. Dorsal and ventral surface of hind femora light brown. Hind femora without dorsal bands. Bottom half of medial area white. Dark stripe along upper carinula. Upper and lower carina without dots. Hind tibiae light brown, with tibial spines brown with black tip.

Phallus: Cingulum , surfaces of rami not infolded in the middle and sinuate, thus making “basal eminence” appear hourglass­shaped and broad in the middle ( Figs. 2 C & 2E). Endophallus, basal valves ventral angle protruding slightly more than dorsal, overall semicircular ( Fig. 2 G). Valves of cingulum pointed, protruding more than apical valves of aedeagus. Epiphallus, distance between lophi shorter than the length of base of a lophus ( Fig. 2 F). Lophi right­triangular.

Female. Much larger than male (total length = 67.5± 4.58 mm; hind femur length = 30 ± 2.60 mm; pronotum length = 15.83± 3.75 mm (n = 3)). Similar to male.

Type Material. 1. PARATYPE Ψ [ BMNH] with labels, “ Socorro I. / RevillaGigedo Is. / III­27­32,” “M Willows Jr. / Collector,” “Templeton / Crocker / Exped. 1932,” “Para­ / type,” “From Collection / Calif Acad Sci,” “ USNM,” “Brit. Mus. / 1981­203,” “Ph,” “32,” “ Schistocerca am. / socoro Dirsh Ψ / V.M.Dirsh det., 1974.” 2. PARATYPE ɗ [ BMNH] with labels, “ Socorro Id. / Brthwte Bay / May 7, 1925,” “H.H.Keifer / Collector,” “Para­ / type,” “From Collection / Calif Acad Sci,” “ USNM,” “Brit. Mus. / 1981­ 203,” “Ph,” “ Schistocerca am. / socoro Dirsh ɗ / V.M.Dirsh det., 1974.” 3. PARATYPE Ψ [ USNM] with labels, “ Socorro Id. / Brthwte Bay / May 7, 1925,” “H.H.Keifer / Collector,” “Para­ / type,” “ USNM,” “31,” “ SCHISTOCERCA / AMERICANA / SOCORO DIRSH / V.M. Dirsh det., 1971.” 4. PARATYPE ɗ [ USNM] with labels, “ Socorro Id. / Brthwte Bay / May 7, 1925,” “H.H.Keifer / Collector,” “Para­ / type,” “From Collection / Calif Acad Sci,” “ USNM,” “22,” “ SCHISTOCERCA / AMERICANA / SOCORO DIRSH / V.M. Dirsh det., 1971.”

Additional Material. 13 specimens (10 ɗ, 3 Ψ) collected during CONABIO­sponsored trip to Socorro Island (October 17­November 5, 2004). Mexico: Colima: Islas Revillagigedo, Isla Socorro . Road to al Volcan in the forest N18o45.494’ W110 o 57.557’ 618 m, 20­X­2004; 40 min. hike up from Senna field (El Paradero) N18o46.331’ W110 o 57.402’ 1716 ft, 25­X­2004; Playa Norte N18o51.527’ W110 o 59.249’ 153 ft, 27­X­2004; Road to Playa Norte N18o46.283’ W110 o 55.595’ 345 m, 26­X­2004; Road to Playa Norte N18o47.172’ W110o 56.031’ 361 m, 26­X­2004; Road to Playa Norte N18o48.011’ W110 o 56.269’ 360 m, 29­X­2004.

Diagnostic Characters. Schistocerca socorro is overall dark brown with no dorsal stripe. This species is only found on Socorro Island and seems to prefer a forest habitat. Two migrant Schistocerca species, S. piceifrons and S. nitens , co­occur on the island, and an angular hind margin of pronotum of the endemic species is a useful character to distinguish it from S. piceifrons , which has a round hind margin of pronotum. Dark patches on tegmina can be used to distinguish the endemic species from S. nitens which has a mottled pattern on tegmina.

Distribution. This species is endemic to Socorro Island, Mexico ( Fig. 3 B). Socorro Island is the largest of four islands comprising the Islas Revillagigedo, located about 480 kilometers southwest of Baja California, México. The type series of S. socorro was collected from Braithwaite Bay, a mixed habitat located at lower elevations of the island. However, a migrant locust species, S. piceifrons , currently inhabits at Braithwaite Bay in large numbers. Recently collected material of S. socorro is all from higher elevations, in the forest in Mt. Evermann and in Playa Norte. This could indicate that the endemic species is limited to higher elevations perhaps due to competitive exclusion (Song et al. accepted).

Biology. Schistocerca socorro is an arboreal species that prefers to feed on native herbaceous plants. It is behaviorally sedentary and is a strong flyer. In early 2003, a group of Mexican officials and researchers working on Socorro Island reported a significant locust outbreak. The locust species was later identified as S. piceifrons , which apparently colonized the island from the mainland Mexico at unknown time. Because of the voracity of the locusts, especially to the native flora, CONABIO (Comisión Nacional para el Conocimiento y Uso de la Biodiversidad) issued a year­long ecological study of the impact of S. piceifrons to the island biota. CONABIO was particularly concerned with the negative impact of the locusts to the endemic Schistocerca species, then known as S. americana socoro . This endemic species had not been collected since 1925. In October 2004, a group of researchers from Universidad Nacional Autónoma de México (UNAM) and I visited Socorro Island and found several sustainable populations of the endemic species. We also identified several ecological differences between S. socorro and S. piceifrons . Although there are areas where two species co­occur, we found that the endemic species is mostly confined to the forested areas in higher elevations, whereas the locust species occur in disturbed areas in lower elevations. We do not know how the endemic species interacts with the locust species, and a continuous monitoring of the population dynamics is desperately needed.

Taxonomic Discussion. Dirsh (1974) originally described Schistocerca americana socoro based on a series collected in 1925 by Hartford H. Keifer and in the California Academy of Sciences. He described it as a subspecies of S. americana , because he reasoned that patterns on hind femora and tegmina were indicative of an affinity to the nominal species, but these characters have since shown to be highly variable and taxonomically unreliable ( Song 2004a). In a phylogenetic analysis, Song (2004a) showed that all the species in the Americana Complex (sensu Harvey 1981) are grouped by a round hind margin of pronotum, which S. socorro lacks. Thus, here I argue for a taxonomic status change from a subspecies to a valid species. Dirsh (1974) also used a subspecific epithet socoro despite the fact that the type label clearly states the correct spelling of the island. Schistocerca socorro is the only endemic grasshopper species on Socorro Island, and I feel it is important for it to reflect the correct name of the island. Thus, I propose a justified emendation of the species epithet from socoro to socorro .

Figures

FIGURE 2. Schistocerca socorro. paratype male dorsal view (A), paratype male lateral view (B), “ basal eminence ” of zygoma (C), ectophallic sclerite (D), cingulum (E), epiphallus (F), endophallus (G), male epiproct (H), male subgenital plate (I), and male cercus (J).

FIGURE 3. Collecting localities of Schistocerca cohni n. sp. (A), and collecting localities of Schistocerca socorro on Socorro Island (B).