The Collaborative International Dictionary of English v.0.48:

Psylla \Psyl"la\, n.; pl. Psyll[ae]. [NL., from Gr. ? a flea.]
   (Zool.)
   Any leaping plant louse of the genus Psylla, or family
   Psyllid[ae].
   [1913 Webster]

WordNet (r) 3.0 (2006):

psylla
    n 1: small active cicada-like insect with hind legs adapted for
         leaping; feeds on plant juices [syn: jumping plant louse,
         psylla, psyllid]