Feeding ecology and evidence for amino acid synthesis in the periodical cicada (Magicicada) Hilary Christensen Q1 a, *, Marilyn L. Fogel b a The University of Chicago, Department of the Geophysical Sciences, 5734 S. Ellis Ave., Chicago, IL 60637, USA b Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Rd., NW, Washington, DC 20015 USA 1. Introduction Q3 First appearing in the scientific literature in the 17th century (Oldenburg, 1666), the synchronous emergences of Magicicada cicada species are a spectacular feature of eastern and central North American ecosystems. Emerging en masse every 13 or 17 years, broods of periodical cicadas can span areas ranging in size from a few counties to a few states in the area of the United States east of the Mississippi River. There are seven known species of periodical cicada in the US, four operating on a 13- year cycle (Magicicada tredecim, M. tredecassini, M. tredecula, and M. neotredecim) and three on a 17-year cycle (M. septendecim, M. cassini, and M. septendecula)(Grant, 2005; Lehmann-Ziebarth et al., 2005). Most broods contain all three or four species, which co-habit in the same areas and operate on identical schedules, yet do not seem to hybridize (Ritchie, 2001). This life cycle, in which the juvenile forms remain in the ground for 13 or 17 years while feeding on xylem fluid from root systems until an unknown mechanism triggers their emergence, is unique among animals (Cheung and Marshall, 1973; Lloyd and White, 1987). Although not the longest-lived insect on Earth, periodical cicadas have the longest juvenile development stage (Williams and Simon, 1995). As adults, they then have approximately 3 weeks to mate and lay eggs before they senesce and perish (Cooley et al., 1995). The eggs hatch 6–8 weeks after oviposition, and the next generation then falls to the ground and burrows down to the roots of the host tree (Williams and Simon, 1995). With numbers reaching into the millions during the 2-week emergence time, periodical cicadas can serve as resource pulses in North American ecosystems immediately after large eruptions (Yang, 2004, 2008). This is an important non-gaseous mechanism for the above-ground transfer of nitrogen trapped in soil reservoirs (Callaham et al., 2000). Due in large part to their underground life cycle and the near impossibility of keeping periodical cicadas under laboratory conditions, however, relatively little is known about the nutrient cycling that takes place during their lives. Since they cannot be easily studied in the wild during the majority of their life spans, the present work aims to investigate this problem without direct observation. This is possible via analysis of stable isotopic variations preserved within the tissues of the participants in this unusual food chain. Journal of Insect Physiology xxx (2010) xxx–xxx 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 ARTICLE INFO Article history: Received 9 October 2009 Received in revised form 5 November 2010 Accepted 6 November 2010 Keywords: Stable isotopes Carbon Nitrogen Insects Cicadas ABSTRACT The periodical cicadas of the genus Magicicada (including M. septendecim, M. cassini, and M. septendecula) have the longest juvenile life span of any insect, living underground for 13 or 17 years and feeding exclusively on root xylem fluids. Due to their inaccessible life cycles very little is known about cicada nutrition, despite the fact that members of Magicicada can achieve a very large biomass in woodland habitats east of the Mississippi and hence constitute a major part of the ecosystem where they occur in high densities. Live cicadas were collected at two sites in early June of 2004, during the emergence of Brood X (both M. septendecim and M. cassini were recovered). We used a combination of stable isotopic measurements (d 15 N and d 13 C) and multivariate statistical techniques to test for differences in resource acquisition among the cicada species and sexes collected at two locations within the 17-year periodical Brood X range. The amino acid constituents of cicada chitin and organs, plus xylem extracted from a deciduous sapling, were also analyzed. The data show that male and female cicadas have different carbon fractionations, which could reflect differential resource utilization due to oviposition in females. Several essential amino acids for the cicada were absent in xylem. Carbon-isotopic composition of all amino acids in the cicadas was distinctly different from the limited set measured in the xylem. Because of the differences in isotopic composition, we conclude that amino acids were synthesized de novo rather than incorporated directly, most likely produced by endosymbiotic bacteria. ß 2010 Published by Elsevier Ltd. * Corresponding author. Tel.: +1 2679683618 Q2 . E-mail address: christensen@uchicago.edu (H. Christensen Q1 ). G Model IP 2599 1–9 Please cite this article in press as: Christensen, H. and Fogel, M.L., Feeding ecology and evidence for amino acid synthesis in the periodical cicada (Magicicada). J. Insect Physiol. (2010), doi:10.1016/j.jinsphys.2010.11.005 Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys 0022-1910/$ – see front matter ß 2010 Published by Elsevier Ltd. doi:10.1016/j.jinsphys.2010.11.005