Assessing habitat and dietary switching by predators in a cover crop system

Project Overview

Project Type: Research and Education
Funds awarded in 2008: $121,092.00
Projected End Date: 12/31/2010
Region: Western
State: Washington
Principal Investigator:

Annual Reports


  • Fruits: pears, general tree fruits


  • Crop Production: cover crops, organic fertilizers
  • Education and Training: demonstration, extension, on-farm/ranch research
  • Natural Resources/Environment: biodiversity
  • Pest Management: biological control, integrated pest management
  • Production Systems: agroecosystems


    In three certified organic orchards and one research orchard we assessed whether an alfalfa cover crop leads to biological control of pear psylla, an insect pest of pears. We monitored predator and pest densities, predator movement and gut contents of predators in alfalfa and control (grass) plots. Pest or predator densities in the trees were not affected by the cover crop, even though the cover crop was found to produce large numbers of predatory insects, with a proportion of those shown to move from the orchard floor into the tree. Specimens collected for the gut contents analyses are being processed.

    Project objectives:

    1. Determine if an alfalfa cover crop leads to an increase in densities of generalist predators in the pear tree canopy;

    2. Examine whether the increased densities of predators in trees having a cover crop understory is due to movement by predators from cover crop to tree;

    3. Assess whether those colonists then switch diet to attack pear psylla;

    4. Determine if the combined effect of habitat and dietary switching then leads to biological control of psylla and a lowering of damage to fruit;

    5. Forward results to growers and evaluate outcomes of the project.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.