Articles
VARIATION IN PEAR PSYLLA (PSYLLA PYRICOLA FOERSTER) DENSITIES IN SOUTHERN OREGON ORCHARDS AND ITS IMPLICATIONS
Article number
124_14
Pages
101 – 112
Language
Abstract
Inter-orchard differences in pear psylla densities are reported for untreated pear orchards in southern Oregon.
Psylla densities in all of the untreated orchards were highest early in the season (April). The number of pear psylla nymphs per leaf at this time ranged from 0.35 to 3.45. Seasonal trajectories of psylla levels followed two general patterns: 1) psylla nymphal densities decreased rapidly, reached levels close to zero by June or July, and showed no resurgence through the rest of the summer, or 2) psylla nymphal densities decreased more gradually and more importantly, rebounded to damaging levels later in the summer.
Predator exclusion experiments, seasonal patterns of psylla predator levels, and psylla densities in insecticide treated orchards indicated that predator activity contributed to the regulation of pear psylla.
Regulation as a result of predator activity was related to the nature of the predator complex and the timing of their presence in the orchard.
The occurence of an early season complex of soldier beetles and green and brown lacewings or snakeflies was an especially important component leading to control.
Biological control of pear psylla is discussed in terms of the management of inter- and intra-orchard habitats to promote these important aspects of predator activity.
Other factors which may contribute to the regulation of pear psylla numbers below damaging levels, such as orchard location in terms of potential for colonization by its predators or manipulation of habitat suitability are also discussed.
Psylla densities in all of the untreated orchards were highest early in the season (April). The number of pear psylla nymphs per leaf at this time ranged from 0.35 to 3.45. Seasonal trajectories of psylla levels followed two general patterns: 1) psylla nymphal densities decreased rapidly, reached levels close to zero by June or July, and showed no resurgence through the rest of the summer, or 2) psylla nymphal densities decreased more gradually and more importantly, rebounded to damaging levels later in the summer.
Predator exclusion experiments, seasonal patterns of psylla predator levels, and psylla densities in insecticide treated orchards indicated that predator activity contributed to the regulation of pear psylla.
Regulation as a result of predator activity was related to the nature of the predator complex and the timing of their presence in the orchard.
The occurence of an early season complex of soldier beetles and green and brown lacewings or snakeflies was an especially important component leading to control.
Biological control of pear psylla is discussed in terms of the management of inter- and intra-orchard habitats to promote these important aspects of predator activity.
Other factors which may contribute to the regulation of pear psylla numbers below damaging levels, such as orchard location in terms of potential for colonization by its predators or manipulation of habitat suitability are also discussed.
Publication
Authors
L.J. Gut, P.H. Westigard, C. Jochums, W.J. Liss
Keywords
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