Xylem feeding by periodical cicada nymphs on tree roots

Abstract. 1. Histological sections of tree roots on which periodical cicada nymphs of both the 17‐year and the 13‐year race arid various instars had fed showed that salivary sheaths made by the nymphs ended in xylem vessels. 2. Because no salivary sheaths were found in phloem cells, this observation indicates that cicada nymphs are xylem feeders throughout their developmental period. 3. The habit of feeding on xylem fluid, which is extremely dilute, may explain why periodical cicada nymphs require so many years (13 or 17) to mature. It may also explain why they excrete amino acids rather than sugars, as phloem feeders do.