Periodical cicada nymphs impose periodical oak tree wood accumulation

Abstract

All deciduous woody tree species of the eastern United States serve as hosts for large numbers of root parasitizing cicada nymphs (Magicicada spp.)^1–4. Periodical cicadas spend their larval lives 6–24 inches underground, feeding on xylem fluid from rootlets and roots⁵. They emerge every seventeenth year in the north or every thirteenth year in the south. Densities of cicadas underground are very great—Dybas and Davis report emergence densities of over 300 nymphs per square yard or about 1,500,000 per acre. This represents the highest reported biomass values of any naturally occurring terrestrial animal⁶. During the adult stage, which lasts 3–4 weeks, cicadas mate and females lay their eggs in twigs of deciduous trees. When the eggs hatch the first instar nymphs fall to the ground to begin their 17-yr development. The damaging effects to twigs by ovipositing adult cicadas is well established^7–13 but the major effect of cicadas may be due to the feeding of nymphs: nymphs are implicated in a reduction in productivity of orchard trees^14–16. However, no studies have compared growth of parasitized and unparasitized trees in the same environment. I report here that feeding cicada nymphs can reduce tree growth, as measured by growth rings, by as much as 30%.