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

2014 Annual Report for GW13-018

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:
Principal Investigator:
Neal Williams
University of California, Davis

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


We continue to work towards completing the objectives outlined in our project measuring the impact of tilling and crop rotations on the squash bee, Peponapis pruiniosa, in Yolo County, California. Specifically, we completed the analysis associated with the tillage study (Objective 1). We are still analyzing the 2013 observational data to determine the relationship between crop rotation history and squash bee density (Objective 2). We began a collaboration with Professor Eric Lonsdorf (Franklin and Marshall College) and his student, Matt Loiacono to continue to develop and validate the simulation model identified in Objectives 3 and 4. We presented our work at two scientific meetings, one departmental seminar, one extension meeting, and one grower field day.

Objectives/Performance Targets

Objective 1: Conduct a manipulative experiment to determine overwintering survival of P. pruinosa under different tillage depth treatments (summer 2013 and summer 2014)

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 (summer 2013 and summer 2014)

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 (fall 2013 – spring 2014)

Objective 4: Validate the model described in Objective 3 with data collected from squash fields in Yolo County (see Objective 1) and grower interviews (summer 2014)

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 (fall 2014)

Objective 6: Develop an interactive website that can be used to show growers how crop rotation practices and tillage practices impact squash bee populations (winter 2013 – fall 2014)

Objective 7: Publish the outcomes of Objectives 1-4 in three papers in peer-reviewed journals (fall 2014)


Objective 1:

We established 20 artificial P.  pruinosa nesting aggregations, each located under a 10 ft x 10 ft mesh cage. Cages were planted with Cucurbita spp. Within each cage we released two female and two male P. pruinosa. We then monitored each cage to track bee nesting activity and floral bloom. At the end of the season, after the females P.  pruinosa  died, we removed the cages. We then randomly selected 10 cages and applied a tillage treatment. The tillage treatment included disking to 15.2 cm, ripping to 40.6 cm with a three-shank subsoiler set at 0.76 m between shanks, and then disking again at 15.2 cm. This is a typical three-year tillage treatment for the study system (Jeff Mitchell, University of California Cooperative Extension cropping systems specialist, personal communication). In the spring we restored the cages to the original location and the trapped emerging bees in each cage. Traps were checked twice a week from May 26 through September 16. Using a Bayesian framework, we found that there was strong evidence that tillage delayed emergence of surviving offspring and moderate evidence that tillage reduced offspring emergence. 


Objective 2:

We monitored P. pruinosa density at and GPSed 95 privately owned squash fields in Yolo County, California. Each field was surveyed three times during the flight period of P. pruinosa. At each field we established four 50 meter transects along which we conducted floral surveys and bee observations. During the 2013 field season we recorded 4,824 P. pruinosa/Cucurbita interactions. At the end of each survey we collected voucher specimens to confirm in-field identifications. GPS data was uploaded into ArcGIS for analysis. We are currently in the process of analyzing this data to determine the relationship between crop rotation history and patterns of P. pruinosa density on farms in Yolo County. Analyzing the data has been more complicated than expected because they are spatially autocorrelated.


Objective 3:

We began a collaboration with Professor Eric Lonsdorf (Franklin and Marshall College) and his student Matt Loiacono to develop a spatially explicit simulation model to explore the impact of tilling and crop rotations on squash bees. We have an excel version of the model but are currently exploring other modelling platforms. 


Objective 4:

When the model is completed we will validate it using data collected from Yolo County squash fields. Grower contacts have been made and interviews will be scheduled for the Spring/Summer 2014. 


Objective 5:

We are in the process of developing fact sheets that will be distributed to the UC Cooperative Extension, Natural Resources Conservation Service ,and non-profits (e.g. Xerces Society for Invertebrate Conservation). We created a “Native Bees” Youtube channel on which we posted three educational videos on P. pruinosa identification and natural history. In addition, we presented our study at a grower field day organized by Rachel Long at the University of California Cooperative Extension. 


Objective 6:

We continued to post on our website ( This website will host the interactive educational model and will eventually be linked to the websites of partner organizations. To date, we have received 995 views of the website. 


Objective 7:

We submitted the paper associated with Objective 1 for publication and presented the work at the Ecological Society of America Meeting, the Entomological Society of America Meeting, and the University of California, Davis Department of Entomology Seminar Series. We are still writing the scientific paper for the outcomes of Objective 2. In the summer, when the model is finalized and tested, we will write the paper for Objectives 3 and 4.

Impacts and Contributions/Outcomes

We presented our work to over twenty extension professionals who attended the Cooperative Extension Advisory workshop organized by the Department of Entomology and Nematology and the Department of Plant Pathology at the University of California, Davis. We also presented at a grower field day that was organized by a local cooperative extension agent. To date, we have had a total of 993 views of the three videos on our “Native Bees” Youtube channel. We are in the process of recording the videos in Spanish. In addition, we developed and translated into Spanish an easy to use squash bee identification guide.


Katharina Ullmann

[email protected]
Graduate Student
Dept. of Entomology, UC Davis
One Shields Ave
Davis, CA 95616
Office Phone: 9707080450
Dr. Neal Williams

[email protected]
University of California, Davis
One Shields Ave
Davis, CA 95616
Office Phone: 5307529358