Periodical cicadas (Magicicada spp.): A GIS-based map of Broods XIV in 2008 and “XV” in 2009

GIS-based and consist largely of county-level records derived from 19th-century USDA maps (Fig. 1; Marlatt 1923) whose low resolution limits their utility for testing hypotheses about brood formation and ecology (Marshall 2001). In addition, existing maps often fail to distinguish between typical emergences, which rely on predator satiation and involve densities of tens of thousands to millions of cicadas per acre (Beamer 1931; Dybas and Davis 1962; Lloyd and Dybas 1966; Dybas 1969; Karban 1982a, b; Williams and Simon 1995) and emergences of small numbers of cicadas or scattered individuals, which may be explained as expressions of latent variation in life-cycle length (“stragglers”; Alexander and Moore 1962; Dybas 1969; Marshall 2001). Even though revisions have corrected some mapping problems (Simon 1988; Kritsky 1992; Irwin and Coelho 2000; Cooley et al. 2009), most broods are in need of detailed, GIS-based study. Of particular interest is Brood XIV, which has a remarkable geographic extent, reaching from New England to Georgia and west through central Tennessee and Kentucky (Marlatt 1923; Simon 1988). It has been suggested that Brood XIV is the source of at least some or all of the other 17-year Magicicada broods (Lloyd and Dybas 1966) through a process of brood formation that involves climate-mediated life cycle mistakes occurring on regional scales (Alexander and Moore 1962). However, these hypotheses are