The Collaborative International Dictionary of English v.0.48:

Pruner \Prun"er\, n.
   1. One who prunes, or removes, what is superfluous.
      [1913 Webster]

   2. (Zool.) Any one of several species of beetles whose
      larv[ae] gnaw the branches of trees so as to cause them to
      fall, especially the American oak pruner (Asemum
      m[oe]stum), whose larva eats the pith of oak branches,
      and when mature gnaws a circular furrow on the inside
      nearly to the bark. When the branches fall each contains a
      pupa.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pruner
    n 1: a worker who thins out and trims trees and shrubs;
         "untouched by the pruner's axe" [syn: pruner, trimmer]
    2: a long-handled pruning saw with a curved blade at the end and
       sometimes a clipper; used to prune small trees [syn:
       pruner, pruning hook, lopper]