Improving Pollination through bumblebee habitation; Evaluation of nest box types in bumblebee colonization

Improving Pollination through bumblebee habitation; Evaluation of nest box types in bumblebee colonization

Summary

Present day commercial agriculture is challenged by the recent dramatic loss of honeybee colonies, which are currently the main pollinators for horticultural crops in the United States. The only sustainable and environmental minded solution to this problem is to encourage farmers to shift their reliance for crop pollination from honeybees to native bees. This can be accomplished by providing the farmer with easy-to-implement methods and suggestions for preserving and enhancing the diversity and abundance of native bee populations. By adopting these recommendations, farmers can ensure free and sustainable pollination, not only for horticultural commodities but also for the ecosystems adjacent to the farm. Subsequent environmental and financial gains will result from the participating farmer’s interest in preserving native bees, such as maintaining a thriving population of pest predators, lessening the farm soil erosion, reducing the use of pesticides, fuel, irrigation water and fertilizer, as well as more windbreaks and weed suppression.

Bumblebees (Bombus spp.), about 45 species altogether, represent one of the most efficient genuses of native bees in North America and have many advantages, including the fact that bumblebees are flower generalists and are active throughout the year. However, based on previous research, it is known that only a small number of overwintering, fertilized bumblebee queens create successful nests. Although the numbers vary somewhat, it is estimated that only 1% of emerging queens develop new colonies. Mice and ant depradation, as well as loss of habitat, are considered to be the primary culprits impacting colony success.

In this project, we proposed to evaluate the success rate in bumblebee colonization of the literature’s most common types of manmade bumblebee nests, along with different ways of installing them.

Objectives/Performance Targets

Based on the research data gathered, we intended to provide the farmers with a set of recommendations including construction plans and practices that growers can use to increase their on-farm success with bumblebees. A second objective was to increase the producers’ awareness of the importance and sustainability of the native bees’ pollination services over those provided by the migratory honeybee.

Accomplishments/Milestones

We have built and installed 120 wooden bumblebee nest boxes on various sites in five farms. We selected the farms based on their geographical and crop production diversity in south-central PA. To further increase the trial’s geographical and environmental setting diversity, we have engaged the public’s collaboration. To that end, we distributed 30 more bumblebee boxes to homeowners, along with factsheets that described the bumblebees’ life cycle and how to install the nest boxes. Both parties, farmers and homeowners, have agreed to keep the area around the nest boxes undisturbed and free of pesticides. Additionally, we advised them to improve and maintain diverse populations of native plants that will bloom successively throughout the year.

In 2008, we trialed two types of wooden bumblebee nest boxes: one type with one chamber, and the other with two chambers (one chamber as a vestibule and the other as a nest). The project also tried to determine, through colonization rates, the level of interest generated by the bumblebees towards manmade nest boxes of different colors. To achieve this, we painted both types of nest boxes in different colors in the subsequent manner: a third of the nests were painted yellow, a third purple, and the rest were simply varnished. The last part of the project sought to establish if the height setting of the nest boxes plays a major role in the queen’s decision about where to colonize. In this regard, we installed the boxes at the following two heights: 16 inches above the ground and six inches above the ground.

The observations were made bimonthly, starting in June 2008. (This allowed the late emerging queens sufficient time to locate and establish a colony. If disturbed in the early part of colonization, the bumblebee queen may leave the brood and nesting site without coming back.) Pictures along with bee samples were taken throughout the season from all the bumblebee nests, with the exception of the nests installed by the homeowners. For the homeowners’ nest boxes, we only made observations when someone indicated to us the presence of bumblebees in their nest box. Samples of bees were submitted for identification to the Penn State University’s Department of Entomology.

Past research of bumblebee manmade domicile colonization has indicated a low success rate, between 0.2% and 5%. Bumblebee nest box colonization is influenced by several factors, including: how numerous and diverse the bumblebee population is in the area, the nest box model used, the location of nest box placement and the time when the nest box was installed. Keeping this in mind, we are able to identify two factors that may have negatively influenced our trial in 2008.

The bumblebee population diversity and abundance in the area. In 2008, we have recorded that the Bombus impatiens is the most prevalent bumblebee species. This bumblebee species is nesting almost exclusively in the ground, in already existent cavities such as abandoned mice nests. In south-central PA, we have recorded two other, less common, bumblebee species: Bombus griseocollis & Bombus vagans. Both of our colonized boxes were occupied by Bombus griseocollis. This indicates that above the ground bumblebee box models are not as successful because they are attractive only for the less prevalent bumblebee species, and not for the predominant one (B. impatiens). This finding has led us to modify the current design in order to have a nest box that will emulate mice nests.

The timing of the bumblebee nest box emplacement. Since the grant funding approval was announced in April, and the nest boxes were installed at the end of the month, it was a little too late in the season for maximum exposure to bumblebee queens searching for nest sites. Although we had our contractor prepared and available to build the boxes, because of the large volume of work required to construct 150 of them, the project could not be completed faster than the two weeks, given the circumstances. Furthermore, the fumes emanated by the fresh paint may have deterred bumblebee queens. In order to eliminate this variable, we will seek support to continue the trial for three years.

The following are the results obtained in 2008 from the bumblebee nest box trial:

Two boxes (1.33% of all the boxes installed) were colonized by the same species of bumblebees, Bombus. Both boxes were 2-chamber models, and were installed 6” above the ground. It appears that the color did not make a difference in the bumblebee choice of colonization, since one box was purple and the other was varnished. Both of the colonized boxes were located in Chambersburg, one in one of the farm hedges belonging to Wilson College, and the other was located on a wild flower field, underneath an eastern red cedar.

Orchard Mason Bees, Osmia lignaria, occupied 15 boxes (12.5%) of the 120 boxes installed on the participating farms. The bees did not show preferences for box’s color, model, or height of which it was installed or location.

With the exception of the boxes installed in full sun, the rest of the boxes were occupied by ants (17 boxes), paper wasps (6 boxes), solitary wasps (1 box), spiders (8 boxes), earwigs (4 boxes), and field mice (2 boxes).

Discussion

As we noted above, the most predominant bumblebee species in Pennsylvania, Bombus impatiens, nests in the ground in preexistent cavities, such as disused mice nests. This has prompted us to modify the design to a nest box model that will better emulate a mice nest. In addition, the new designed box will accommodate on top of it bamboo shoots as solitary wood-nesting bee nests, and will also provide, through the sand mound that will cover the entrance for the bumblebees, habitat for the ground-nesting bees as well. The bee nest will be built of an recyclable plastic and wood composite material. This material will prolong the nests life span, unlike the wood, which is proven to crack, warp, and rot. The new bee nest will provide nesting habitat for a variety of bees (solitary and social / wood nesting and ground nesting), which will enhance the pollination services for a variety of crops, starting from early spring through late fall.

Impacts and Contributions/Outcomes

Both farmers and the general public have shown a lively interest and support for this project. While specific contributions cannot be identified at this point because the program is still in its early stage, through the development of this project we have raised the awareness of the importance of native pollinators. A series of talks, field days, and educational materials have been developed and shared with the public. Moreover, we have started several projects on native bee conservation directly because of the work we have completed for this grant. We strongly believe that these types of research projects will be the cornerstone for changing our current pollination management to a more sustainable one.

Beside of numerous mentions in the Pennsylvania’s south central newspapers, we have made the work and results obtained from this project public through several outreach efforts:

Talks:

Franklin County Beekeeper Association meeting (Coop. Extension Office) – 30 people

Wilson College’ Farm field day (Fulton Farm) – 20 people attending

Summer Garden Experience (Penn State Research Farm) – 45 people (workshop)

PASA field day at the Dickinson College (Dickinson College Organic Farm) – 30 people

FREC Open House (Penn State Fruit Research Lab.) – 15 people

Factsheets:

Migratory beekeeping – Second Thoughts…

B-stings!

The Queen’s Life Understanding Bumblebees

Understanding Bumblebees

Moreover, in the incoming year we have planned several other meetings and publications relating to the work and experience gained through this project.

Because the project is in the development stage, we have not yet encouraged any large-scale farmer adoption. However, we believe that after another year the project will allow us to make precise recommendations on what type of bee nest boxes and practices farmers should employ in order to acquire pollination sustainability.

Collaborators: