Evaluation of the Utility of Adding Artificial Bumble Bee Nesting Sites to Increase Pollination Services in a Small Farm Environment

Evaluation of the Utility of Adding Artificial Bumble Bee Nesting Sites to Increase Pollination Services in a Small Farm Environment

Summary

The first trial was completed, with no occupancy (N = 96). Additional nest boxes (N = 200) have been constructed and placed for the 2013 trial. A new insulation design has been planned and is in construction for 50 of these boxes. On-farm bumble bee diversity and abundance was determined through standardized, 30-min sampling bouts allowing a comparison with other, non-farm sites in the region. Bumble bee abundance and diversity were lower on the farm. There seem to be differences in flower preference between species. Bi-weekly surveys will begin again in April.

Objectives/Performance Targets

A total of 96 artificial nests were installed at two farm locations under a factorial design. Nests were inspected bi-weekly, and on-site estimates of bumble bee diversity, abundance and floral preferences were conducted concurrently. None of the artificial nests were occupied by Bombus queens. Bumble bee diversity and abundance measures were compared with other sites in the region to compare farm populations to non-farm sites. Bumble bee preference for crop plants was investigated using data collected at Horn Family Farms.

For the second-year trial, 200 artificial nests have been installed at Horn Family Farms, still incorporating the same factorial design as year one. In discussions with colleagues working in the same field, a new design for the insulating material will also be incorporated. In Norway, Atle Mjelde has had high occupancy rates utilizing an artificial mouse nest (AMN) design as insulation within wooden nest boxes. The principle behind the AMN is basic mimicry of the structures constructed by rodents that Bombus queens utilize in nature. A hollow sphere about 10cm in diameter is constructed, with fine dried grass on the exterior, lined with finer cotton insulation material, which is them lined with kapok, a very fine plant fiber that mimics rodent fur. Access to the interior of the AMN is provided by a 2.5 cm hole to the exterior, and the entire AMN is placed within the wooden nest box. Fifty of these are under construction presently, and will be placed into the already installed boxes before Bombus queen emergence (expected at the end of March). Bumble bee occurrence and plant preference data will be continued throughout year two.

In the first year’s trial, none of the nests were occupied by Bombus queens at either farm location. An improved design will be implemented in 2013, with 200 boxes at a single farm. Fifty of these boxes will have a new insulation design.

The species diversity and relative abundance have been systematically sampled in year one. This should provide a baseline for comparison in year two, should any nest boxes become occupied.

Dates that crops were in bloom were recorded April – October of 2012. Bumble bee surveys were conducted concurrently, with floral hosts noted. These data will be combined with other bumble bee survey data from the region to characterize the seasonal phenology of both bumble bees and crop blooms in the area.

Data from crop and bumble bee phenology will be combined with the results of the nest box trials to develop region-specific information for farmers at the end of year two.

Accomplishments/Milestones

No bumble bees were observed near the nest box areas of the University farm site in 2012. Bumble bees were present at the Horn Family Farm site, but both abundance and diversity were quite low. Only four of the expected six species were observed (see Table 1). To determine how bumble bee diversity on Horn Family Farms compared to data at other site types, Shannon’s Diversity Index (H) was calculated. As part of another study, the researchers have used the same standardized sampling methods at other sites in the region over the same period (n = 13, including prairies and vacant lots). These data provided the material for comparison. At non-farm sites in 2012, H = 1.99, with estimated HMax = 2.58. At the study farm, diversity was lower, with H = 1.56 and HMax = 2. This indicates that farms could benefit from practices, such as artificial nests, that improved bumble bee abundance and diversity.
There were also differences in the seasonal occurrence of each bumble bee species. No bumble bees were observed on the farm site until the first week of June (Table 1), despite their presence at other site types in the region since early April. This indicates a need for improving the presence of early season species, such as B. auricomus, which was notably absent (Table 1), if pollination services are to be achieved on the farm prior to summer.

Pollination is the end goal of improving bumble bee numbers on farm sites. There may also be differences between the floral preferences of different bumble bee species. To investigate the relationship between bumble bee species and crop bloom, a pollination network map was constructed (see Figure 1). Only two crop species were recorded as being visited by bumble bees at the site during 2012, okra and beans. Of the four bumble bee species present, only B. impatiens and B. pensylvanicus were observed on crops. The other two species were seen on wildflowers surrounding the site, which both B. impatiens and B. pensylvanicus also used. However, overall sample numbers were low (n = 40), and B. bimaculatus and B. griseocollis were less abundant than the other two species. The resulting pollination network may be an artifact of sampling rather than being indicative of real patterns. Additional data from the second year of the experiment should help determine the true pollination network patterns at the farm site.

• Figure 1. Pollination network map showing relative numbers of bumble bees by species seen on crops and wildflowers at the study site in 2012.
• Table 1. Bumble bee abundance on site by species and sample date.

Impacts and Contributions/Outcomes

None yet, but this project aims to determine if providing artificial nesting sites will increase the abundance or alter the diversity of bumble bees on small-scale farms. It also aims to determine the relationship between crop bloom times and bumble bee phenology in the region. The results of this research should provide recommendations to farmers seeking to improve fruit set utilizing native bumble bee pollinators.

Collaborators: