Periodical cicada (Homoptera : Cicadidae) life-cycle variations, the historical emergence record, and the geographic stability of brood distributions

The complex biogeography of the 13- and 17-yr periodical cicadas offers imp ortant opportunities for testing hypotheses of Magicicada evolution and eco logy. However, misinterpretation of stragglers as on-schedule emergences, c ombined with systematic biases in search effort and the use of cross-genera tional brood maps, likely results in erroneous edge extension of adjacent b roods and the appearance of sympatric shadow broods in published maps. Subs tantial recent changes in brood distributions have been inferred from the M agicicada historical record, the most significant being the decline and ext inction of 17-yr brood X in tile midwestern United States, the widespread e xpansion and contraction of 17-yr brood VI and 13-yr brood XXIII, and the d isplacement of brood XIII 17-yr cicadas in Illinois by 13-yr brood XIX in I llinois. Reanalysis of the historical data with an awareness of straggler-i nduced error suggests instead that brood distributions in these cases have remained stable.