Bioacoustics of Schistocerca socorro

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 .

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).