Best management practices that promote sustainable crop pollination: the role of crop rotations and tillage depth

Project Overview

Project Type: Graduate Student
Funds awarded in 2013: $24,954.00
Projected End Date: 12/31/2015
Grant Recipient: University of California, Davis
Region: Western
State: California
Graduate Student:
Major Professor:
Neal Williams
University of California, Davis

Annual Reports


  • Vegetables: cucurbits
  • Animals: bees


  • Crop Production: conservation tillage
  • Natural Resources/Environment: wildlife
  • Production Systems: general crop production


    Wild, native pollinators contribute to crop pollination. Management practices to support these pollinators will need to include strategies that can be implemented across the entire farm, including crop fields. This project explored how tilling and crop rotation practices impact an important pollinator of squash and pumpkin, the squash bee (Peponapis pruinosa). We found that for this ground nesting bee tilling can have a negative impact on offspring emergence. In addition, the location of squash fields, through time, impacts squash bee densities in squash and pumpkin fields. Both management practices impact squash bee population growth according to the spatially explicit simulation model that we developed. We used a variety of outreach tools (workshops, fact sheets, an on-line tool, and videos) to raise grower understanding of squash bees and farm practices that can support these important crop pollinators.


    Pollinators are essential for the production of some crops. Farm management strategies to support pollinators have typically focused on resource intensive, field border practices such as seeding wildflower strips or planting hedgerows (Garibaldi et al. 2014). While field border practices are important, few studies have explored the value of within-field practices to support pollinators.

    Crop fields can provide important resources for bees. For, example flowering crops provide pollen and nectar (e.g. Williams and Kremen 2007). Crop fields also provide nesting sites for ground nesting bees (Kim et al. 2006). While crop fields can benefit bees, practices associated with agricultural intensification negatively impact these important crop pollinators (Williams et al. 2010). For example, if bees prefer nesting in fields, tilling can kill overwintering offspring. In addition, annual crop rotations can create landscapes where resources provided by flowering crops can vary in space and time. If a bee is a specialist it will need to “track” these resources in order to persist in the landscape.

    Squash and pumpkin (Cucurbita spp.) are dependent on pollinators to set fruit. Growers rent honey bees for pollination, but colony collapse disorder, pests, and diseases threaten this species. Wild, native bees also pollinate Cucurbita crops. For example, squash bees (Peponapis pruinosa) are as efficient as honey bees in pollinating squash (Tepedino 1981). Squash bees are ground nesting bees that specialize on plants in the genus Cucurbita. While a potentially important crop pollinator, the abundance of this species may be limited by tilling and crop rotation practices.

    Project objectives:

    Objective 1: Conduct a manipulative experiment to determine overwintering survival of P. pruinosa under different tillage depth treatments

    Objective 2: Conduct an observational survey to determine if crop rotations that promote between-year connectivity (i.e. how connected a focal Cucurbita field is to surrounding Cucurbita fields through time) have larger P. pruinosa populations than crop rotations that have low between-year connectivity

    Objective 3: Build a spatially explicit simulation model that uses crop rotations and tillage practices to predict P. pruinosa abundance and use this model to identify optimal management strategies

    Objective 4: Validate the model described in Objective 3 with data collected from squash fields in Yolo County (see Objective 1) and grower interviews

    Objective 5: Communicate best-management practices using existing UC Cooperative Extension, Natural Resources Conservation Service, and non-profit (e.g. Xerces Society for Invertebrate Conservation) partnerships

    Objective 6: Develop an interactive website that can be used to show growers how crop rotation practices and tillage practices impact squash bee populations

    Objective 7: Publish the outcomes of Objectives 1-4 in three papers in peer-reviewed journals

    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.