Genus Schistocerca (Acridomorpha, Insecta).
This revision of the genus Schistocerca introduces some important changes in nomenclature. In view of the multiplicity of forms in the genus, the recognition of species and subspecies in it is somewhat complicated, and it has been suggested that all the species form one cline. However, the author adopts more conventional classification. He recognises 22 undoubted species, three of them with subspecies, and these are reviewed and described, with keys for their separation. Six species and four subspecies are new.Since it is not specifically distinct, S. gregaria (Forsk.), the well known 'desert locust' of the Old World, is made a subspecies of S. americana (Dru.), the migratory locust of America, this name having date priority [cf. RAE/A 55, 536], and as such occurs in two morphometrically different forms, compressa and tectata. These correspond to the earlier so-called phase gregaria and phase solitaria in their extreme forms and can be differentiated by the F/C ratio (ratio of length of hind femur to width of head). The other subspecies of S. americana, apart from the typical one occurring in the United States, Mexico, Central America and parts of the north of South America, are benedicto subsp. n., from the Pacific island of St. Benedicto, cancellata (Serv.) [45, p.327; 55, 536], from Mexico and many South American countries, sometimes as a migrant, cubense (Sauss.), from Cuba, the Bahamas, Jamaica, Trinidad and other islands, flaviventris (Burm.), from southern Africa, interrita Scud., from parts of South America, paranensis (Burm.) [cf. 45, p.327; 55, 536], from almost the whole of South America east of the Andes and migrating to western parts and the West Indies, peruviana Lynch Arrib., from Peru, serialis (Thnb.), from coastal Florida and the West Indies, and socoro subsp. n., from the island of Socoro in the Revilla Gigedo group. These are all described and numerous synonyms are cited, some of the synonymy being new. The two other species that have subspecies, some of them new, are S. alutacea (Harris) and S. nitens (Thnb.).Synonymy affecting names mentioned in this Review includes S. nitens nitens (australis Scud., impleta (Wlk.), vaga (Scud.)), S. flavofasciata (Deg.) (infumata Scud.), S. americana cubense (inscripta (Wlk.)), S. americana americana (piceifrons (Wlk.), rustica (F.)), S. alutacea shoshone (Thos.) (venusta Scud.) and S. americana cancellata (vicaria (Wlk.)).The new species described are S. beckeri, from Trinidad, S. braziliensis, from Brazil, S. centralis, from Central America and Mexico, S. gorgona, from Gorgona Island, S. matogrosso, from Brazil, and S. orinoco, from Venezuela.Migration in species of Schistocerca is discussed in an introductory chapter, the main migratory forms being S. americana americana in North America and S. americana gregaria in the Old World. Mass multiplication occurs not only in these but also in S. pallens (Thnb.) in the Americas. The late Sir B.P. Uvarov introduced the 'phase theory' to explain the occurrence of polymorphism and migration in locusts [9, p. 561], but the theory was later modified under the influence of other authors, and Uvarov in his latest book [54, p. 184] departed considerably from it in its original form, proposing to use the words 'crowded' and 'solitarious' for 'gregarious' and 'solitary'. It now appears that any 'phase' of S. americana gregaria may produce swarms and migrate. The author concludes that there are two morphologically different forms of the subspecies (compressa and tectata) connected by continuous series of intermediate forms. Their behaviour may or may not be correlated with their morphological characters. Study of very extensive material has indicated that S. americana gregaria comprises populations of continuous variation. The term 'phase' should be suppressed in this connection.