|Abstract or Summary
- This thesis addressed the potential of endemic predaceous and parasitic arthropods of
the Hood River Valley, Oregon to suppress the pear psylla, Cacopsylla pyricola F8rster.
Natural enemies adequately suppressed psylla in three of seven unsprayed orchards of
differing vegetational settings, orchard age, and size. Relatively few psylla natural enemies
dispersed to unsprayed pear mini-orchards, dspite abundant populations on surrounding
noncultivated vegetation. Pear psylla natural enemies were more abundant on arboreal rather
than herbaceous non-pear hosts. Selective programs of pear pest control based on
diflubenzuron were moderately successful in controlling the pear psylla, with natural enemies
aiding in suppression in six of fourteen commercial trials of selective programs. In both
unsprayed and commercial pear orchards, late-season psylla densities appeared to be best
suppressed when levels of natural enemies were high during early-season. Classification
analysis confirmed that orchard site, chemical regime, type (mini- or commercial), and season
affected proportions of natural enemies and their pear psylla prey. Complexes of natural
enemies and pear psylla immatures from commercial orchards where biological control was
successfully demonstrated were taxonomically similar. Effective natural enemy complexes in
commercial orchards were characterized by earwigs, lacewing larvae, and moderate
proportions of pear psylla immatures during early season and Deraeocoris brevis, earwigs,
and lacewings during mid-season. Plagiognathous guttatipes (Uhler) or Diaphnocoris
provancheri (Burque) dominated effective natural enemy seasonal complexes at each of two
The functional response to pear psylla eggs was measured for five predaceous mirids.
Functional response parameters differed among species and their life-stages, but all destroyed
large numbers of psylla eggs.
Further experimental directions for the implementation of pear psylla biological
control are proposed. General investigative strategies include: (1) augment natural enemies on
non-pear vegetation adjacent to the target orchard, and (2) modify the orchard habitat to both
encourage natural enemy colonization and allow permanent complexes of natural enemies to
develop. Specific tactics include: plant hedgerows of filbert or willow, cultivate snakeflies,
introduce Anthocoris nemoralis, adjust early season psylla densities with suitable timing and
kind of delayed dormant sprays, using a more effective selective psyllacide, and reduce winter
pruning to allow development of natural enemies which overwinter in the egg stage.