摘要 : Aunique and dramatic North American phenomenon in early spring is the emergence of hordes of adult periodical cicadas. These large numbers of adults emerge from the soil over vast areas of wooded or shrubby regions of the nation a... 展开 Aunique and dramatic North American phenomenon in early spring is the emergence of hordes of adult periodical cicadas. These large numbers of adults emerge from the soil over vast areas of wooded or shrubby regions of the nation after an absence of many years. Both adults (above ground) and nymphs (on roots in the soil) feed on xylem sap, which is well over 90% water most of the year. Up to six million cicadas may occur per acre. They all die and disappear after two to three months, not to be seen again in those same areas for 13 or 17 years. These are Periodical Cicadas (Magicicada, including three species of 17-year cicadas and four species of 13-year cicadas), daytime loud-singing and flying insects that cannot be ignored. They occur in populations covering substantial geographic areas, but do not emerge over the whole of eastern North America in the same year, and emerge as chronologically and geographically separated populations called broods, designated by Roman numerals (Figs. 1 and 4; Alexander and Moore, 1962). 收起