Development of best use practices on commercial colonies of Bombus impatiens on crops in Delaware
To help combat pollinator shortages, mainly those of honey bees, and meet the pollination requirements of important agriculture crops, researchers and growers are investigating the effectiveness of native pollinators in larger agricultural settings. A common native pollinator in Delaware is the Common Eastern Bumble Bee (Bombus impatiens). Growers are interested in utilizing this native pollinator commercially, and many growers are starting to use bumble bees units in their fields. To-date there has been no research conducted in Delaware (and in most other states) that addresses how to best use these commercial bumble bee colonies in various crops and under differing field conditions. Consequently, there are few crop or site specific management strategies available for growers to enhance the performance and extend the longevity of these units (Desjardins and Oliveira 2006).
In collaboration with four commercial growers, bumble bee colony growth was measured over the season in different crops, the recommended number of colonies per acre was manipulated to ascertain the necessary number of units in the field, placement effects were examined, and overall bumble bee health and survival was assessed. We also examined the horticultural effects on yield and quality of harvested crops. By studying these factors we determined how to best use these native pollinators which will hopefully increase crop yields for growers.
Specifically, we are developing best management practices for commercial bumble bee units in cucumbers, watermelon and strawberries in the state of Delaware. These crop specific, best management practices will provide growers with guidelines on the most efficacious use of bumble bee units for their area.
In the growing season of 2012, 42 bumble bee quads were purchased from Koppert Biological Supply Company and were placed in four different crops; strawberry, watermelon, pickling cucumber, and pumpkin. Two quads were utilized for the strawberry crop. Obtained in March, the strawberry quads were placed in a sunny area along the edge of the strawberry field with shade structures and temperature recorders. These quads were visited weekly to conduct five minute foraging counts on each of the four colonies per quad.
During the first week of June, thirty quads were obtained for the watermelon crop. These quads were distributed evenly between three different fields of varying sizes. Upon placement, each quad was randomly assigned to a placement treatment that determined the nature of how it would be placed in the field. Quads were either placed in direct sun, natural shade or assigned a shade structure. Three temperature recorders were available per field and randomly assigned to a single colony of a different placement treatment. In other words, one colony per one of the three placement treatments received a temperature recorder, per field. All colonies of each quad were tested weekly for five minute foraging counts and weight, to the nearest 0.5 gram. In the beginning of July the highest and lowest weighing colonies per field were sacrificed and dissected for comparisons between colony weight and colony cells and the number of bees found in the colony.
During the second week of July, ten additional quads were obtained to be placed in a single pickling cucumber field. Placement treatments in the pickling cucumbers were either sun or shade structure. Temperature recorders were also placed in colonies of different treatments. All colonies were examined weekly for five minute foraging counts and weight to the 0.5 gram. Additional foraging data within the pickling cucumber was gathered. These additional tests included counting the number of flower visits per minute/bumble bee, sweep netting pollinators along five, 50 meter transects for 30 minute intervals and counting honey bees, squash bees and bumble bees flying into and out of a 1mx1m area at each 5 meter interval along the transect. Quads were removed just prior to pickling cucumber harvest and placed in a second pickling cucumber field. Quads in the second field were overrun by honey bees and were then placed in a pumpkin field until the end of the season.
Each hive was dissected at the end of the season or whenever it is found dead. Dissection methods include obtaining weight of the wax, counting the number of queens, workers and males in the nest and recording other found nest commensal organisms. Wax and bees within the colonies were sent off to the USDA for pesticide analysis
Crop product information was obtained for watermelon and pickling cucumber.
In watermelon, fruit set and fruit yield data were obtained. When examining the field for fruit set, 5 plants at varying distances from each quad (10, 20, 30, 40 and 50 meters) were located and the number of fruit (at least as large as a softball) were counted. Fruit set test was conducted twice in each field during the season. The first was conducted when fruit in the field were the average size of a softball and again just prior to the first harvest. Finally, fruit yield data were obtained in one of the three watermelon fields, just prior to each harvest. A 10 meter transect adjacent to each quad was flagged and all harvestable fruit within the transect was harvested and weighed.
Crop yield data was gathered by harvesting eight, 10 yard plots on various areas of the first pickling cucumber field. GPS data points of each plot were taken to mark distance from bee quad. The weight of pickles harvested in each transect was recorded. This experiment was not run in the second pickling cucumber field because of the hasty removal of the bumble bees to avoid being overrun by honey bees. ]
A pollen transfer experiment was attempted in both pickling cucumber fields. This experiment focused on the bumble bees’ ability to transfer pollen from flower to flower. Flowers were bagged with paint strainers the day before anthesis. The next day, experimenters attempted to control bumble bee visits to the isolated flowers. This experiment was not successful, as so few bumble bees were present in the field to pollinate these flowers.
Another aim of this project is to disseminate project information to the public. In 2012, the project was presented four times to public audiences. In January a presentation was given during the Vegetable Crop Section of the Delaware Agriculture Week Meeting in Harrington, Delaware. A presentation was given in April to the New Castle County, DE Beekeeping Association monthly meeting. Members of the audience were honey beekeepers of the county in which the University of Delaware resides. In June, a presentation was given at the Bumble Bee Conference at Utah State University in Logan, UT. After this presentation, a meeting was held with members of the USDA-ARS lab situated on Utah State’s campus and new ideas were solicited and discussed. Finally, in November of 2012 a presentation was conducted at the Entomological Society of America Annual Meeting held in Knoxville, TN. Three thousand professional entomologists from all over the country were in attendance at this meeting. The given presentation was held in a session for pollinators and all meeting attendees had access to the presentation.
- • Create pollen reference library on pollen collected from foragers (January 2012 – February 2012) Still in progress (adding 2012 pollen to this library in December 2012- January 2013)
• Second year of trials: March 2012-October 2012
o Conduct foraging and productivity in strawberry fields (March 2012 – July 2012) Completed as indicated
o Conduct foraging and productivity trials in watermelon fields (May 2012 – September 2012) Completed as indicated
o Conduct foraging and productivity trials in pickling cucumber fields (July 2012 – October 2012) Completed as indicated
o Evaluate bumble bee loss and pesticides in colonies in selected fields (July 2012 – December 2012) Completed as indicated
• Study progress presented at meetings (on-going) On-going, as indicated
• Best management practices developed (November 2012) New targeted completion date, Spring 2013
• Best management practices distributed in written form and posted in electronic form (December 2012) New targeted completion date, Spring 2013
• Best management practices presented at winter meetings (December 2012 – April 2013) New targeted completion date, Spring – Summer 2013
o Pollen transfer study, as explained above, bumble bees were not present in the field in necessary numbers to make this experiment realistic
o Honey bees attacked bumble bee colonies in the second pickling cucumber field, causing bees to be removed and placed in a pumpkin field. This prematurely ended the examination of bumble bees in pickling cucumbers.
Impacts and Contributions/Outcomes
Please see uploaded file for current summary of results.
University of Delaware
16483 County Seat Highway
Carvel Research and Education Center
Georgetown, DE 19947
Office Phone: 3028567303
University of Delaware
531 South College Ave
Newark, DE 19716
Office Phone: 3028311464