A Revision of the Genus Locusta, L. (= Pachytylus, Fieb.), with a New Theory as to the Periodicity and Migrations of Locusts

Abstract

The genus Locusta, L. (= Pachytylus, Fieb.) includes two of the most destructive swarming locusts of the Old World: the widely distributed L. migratoria, L. (with L. danica, L., and L. migratorioides, Rch. & Frm., as its forms; see below), and the South African L. pardalina, Walk. The literature on the economics, biology and especially on the means of control of these locusts is enormously extensive, but at the same time their systematic arrangement is in considerable confusion, and extremely contradictory opinions as to the mutual relationship of the different so-called species exist among specialists. As a direct consequence of this, the field research and control work of economic entomologists is apt to suffer through the difficulty in getting a particular species properly named, and thus it is often impossible to make a comparison of the records as to the biology and control of the same species in different countries.

Phase-Dependent Color Polyphenism in Field Populations of Red Locust Nymphs (Nomadacris septemfasciataServ.) in Madagascar

“…Individuals are either of two extreme phenotypes: solitarious or gregarious [1,2]. This polyphenism is continuous and all the intermediate stages, transiens, congregans or dissocians, are found between the two extreme phases, depending on the direction of the transformation.…”

Molecular and morphological evidence for hybridization between two ecologically distinct grasshoppers (Melanoplus sanguinipes and M. devastator) in California

“…Traits used to distinguish species may be plastic responses to different environments rather than genetically based markers of reduced gene flow (Geist, 1992). A classic example of this was phase polyphenism in locusts, which resulted in the different phases of these insects being originally classified as separate species (Uvarov, 1921). In arthropods, male genitalic differences are often used to distinguish species, yet divergence in genitalia may not physically impede copulation (Robson & Richards, 1936;Shapiro & Porter, 1989;Porter & Shapiro, 1990; and divergently in separate populations (Eberhard, 1986).…”

Increased muscular volume and cuticular specialisations enhance jump velocity in solitarious compared with gregarious desert locusts,Schistocerca gregaria

“…Swarms may contain billions of individuals covering hundreds of square kilometres, and are occasional events triggered by changing environmental conditions in the arid regions that this species normally inhabits (Steedman, 1990). Central to swarm formation is the ability of locusts to transform reversibly between a lone-living solitarious phase and a group-living gregarious phase, depending upon population density (Uvarov, 1921(Uvarov, , 1966Ellis, 1959;Simpson et al, 1999;Pener and Simpson, 2009). This remarkable phenotypic plasticity results in locusts that differ extensively in many aspects of their behaviour, physiology and morphology (Dirsh, 1953;Roessingh et al, 1993;Roessingh and Simpson, 1994;Simpson et al, 1999;Rogers et al, 2004Rogers et al, , 2007Rogers et al, , 2014; Lester et al, 2005) (Fig.…”