Optimization of Greenhouse Crop Pollination through Artificial Homeostatic Control of Bumblebee Hive Temperature

Progress report for GNE19-222

Project Type: Graduate Student
Funds awarded in 2019: $13,931.00
Projected End Date: 05/30/2022
Grant Recipient: The Pennsylvania State University
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:
Dr. Rudolf Schilder
Penn State University
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Project Information

Project Objectives:

Objective 1: Determine how artificial homeostatic control of colony temperature affects pollination services relative to a traditional commercial colony box.

Objective 2: Quantify how much time workers spend wing fanning or brood incubating in temperature-controlled colonies compared to a traditional commercial colony box.


Pollinator populations are declining worldwide, while food and crop demand continually increase. Therefore, growers have to rely more heavily on commercially available pollinator colonies. While honey bees are a popular choice, some crops can only be pollinated through buzz pollination, or need pollination service across a wider range of environmental temperatures than honey bees can supply. Commercially available bumblebees provide these features, and to help meet food and crop demand increases, there is therefore a need to examine ways in which we can optimize the efficacy and health of bumble bee colonies

Bumble bees are increasingly used to fulfill pollination needs, as they provide a less labor-intensive process compared to mechanical pollination. Bumble bees are highly effective pollinators, but have interests that compete with foraging (and therefore pollination) associated with colony survival. One of these is the need to regulate brood temperature within a specific range to ensure proper development of larvae. Bumble bees task switch between colony maintenance and foraging so any worker occupied with brood thermoregulation will not forage, resulting in decreased pollination service. My work looks to examine if by enhancing brood thermoregulation artificially, it will enhance the number of foraging workers and increase pollination service.


Materials and methods:


Figure 1: The temperature controlled box with an unmodified bumble bee colony box placed inside to show orientation

A temperature controlled colony box has been developed and has been tested to hold temperature independent of ambient temperature (Figure 1). The temperature controlled box is built using plywood, insultation, and tubing running through the box. The tubing is the same material used for cold and hot water circulation in homes. A circulating water bath maintains the internal temperature around 29 °C by flowing water from the water bath through the tubing in the box. Inside of the temperature controlled box is a platform the colony rests on, but access to their sugar box (which is provided to us from the commercial bee supplier), is not obstructed. It is important that the colony maintains access to their sugar throughout the pollinating season, as the most common crop bumblebees pollinate, tomatoes, does not provide enough nectar for colony survival, and it is therefore recommend that the sugar box provided be utilized. 

Figure 2: A modified colony lid

The lid of the colony box will be removed and replaced with a modified lid (Figure 2). This allows the cameras a more unobstructed view of the colony. A wooden frame holds chicken wire in place. Chicken wire is used as bumble bees are unable to chew through this material. The chicken wire does offset the thermal camera readings by 1 °C. In addition to knowing that it consistently is off by a degree, a thermal couple will be placed inside of the colony box to read the background temperature, allowing for calibration of the thermal camera. 


Figure 3: A plywood box covered in fabric to shade the bumble bee colony. The two holes hold a thermal camera and a DSLR camera

Above the colony box, a camera stand was constructed (Figure 3). The camera stand is built so that shading material is provided between the cameras and the colony. In field settings, the bumblebee colony is recommend to be placed in a shaded area, and the cardboard surrounding the colony remains un-altered. In order for us to film activity inside of the colony, the cardboard had to be altered with the top removed, and the lid of the colony replaced with our modified lid. We therefore provided a shading structure to keep bumblebee colonies darker. There are two holes in the camera stand, one for a thermal camera, and one for a digital camera. When recording, a red light is turned on inside of the shaded stand. As bumblebees do not see in red light, this is the least obtrusive way of providing enough illumination for video footage.

For the experiments, bees inside of the colony box are removed, immobilized, and then a QR code is glued to the back of their thorax. The digital footage recorded is then analyzed through BEEtag (Crall, Gravish, Mountcastle, & Combes, 2015). BEEtag is a software program which is able to track the movement of bumble bees over time by tracking the unique QR code on each bee. This software will be utilized to indicate when bees are entering and leaving the colony, and how long a bee is standing in a specific spot. This can be used to identify which bees may be performing in wing fanning, a thermoregulatory trait. Because the tags utilized cover the thorax, measurements obtained from the thermal camera will be off. To counter this, test bees will be utilized to determine how much the tag alters thermal measurements. Bees will be randomly selected and placed in an observation chamber to see what thoracic temperature they achieve. Bees will then be immobilized, and half of the bees will be tagged. All bees will then be placed individually back in the observation chamber to see what temperature they achieve after being tagged. The offset between tagged and untagged bees will then be used to normalize the thermal camera measurements. For example, tagged bees could show as one degree cooler than untagged bees. All colony measurements made then would need to have one degree added to counterbalance effects from being tagged. 


Figure 4: The flight arena is connected to the colony via PVC tubing. Picture is without the camera stand. This is showing a non-temperature controlled colony

Colony boxes are connected to a flight arena via PVC tubing (Figure 4 and 5). As this tubing is the only way in and out of the colony, this helps keep all bees within focus of the cameras, and prevents bees flying into the cameras. In addition to the digital camera tracking when a bee is entering or exiting the colony area, two adjacent break beam sensors are placed along the PVC tubing (not shown). An Arduino program records the order that the beams are broken, which indicates if a bee is exiting or entering the colony. This data can then be used to inform us how long a bee was foraging outside of the colony. This helps ensure that bees are truly leaving to forage, rather than just being on the peripheral of the colony and not contributing to colony duties. 

Figure 5: A flight arena attached to a colony and shade stand. The petri dish holder is on the far left and is accessible via a latched door

Originally the plans called for utilizing tomatoes grown in a greenhouse to measure pollination services. Anther cone bruising on tomatoes would be used to measure the amount of pollination occurring. However, due to the Coronavirus, it was not, and continues to not be feasible to perform greenhouse work. Instead, a proxy for pollination services will be used by looking at the amount of pollen bees collected. Additionally, the amount of times bee enter and exit, and the amount of time spent foraging will also be quantified. The experiments will instead take place in a growth chamber. Inside of the flight arena, there will be a petri dish full of pollen. The pollen will be weighed daily before being placed in the arena and at the end of the day to inform us how much pollen is collected each day. 

Originally, the plans called for looking at both infected and non-infected colonies. Unfortunately, this is no longer feasible for a couple of reasons. During the pandemic, the -80 freezer malfunctioned so all the stocks of Crithidia bombi used to create infected colonies. Getting new stocks is costly, time intensive, and not a guarantee. The space in the growth chamber is considerably smaller so not as many colonies can be run simultaneously, which increases the amount of time needed to perform the experiments. Cultivating C.bombi is also sensitive and must be managed almost daily, and given the uncertainty because of the pandemic, makes this not feasible. Due to the reasons stated above, dropping the infected colonies is prudent. 

A growth chamber will be used to manipulate ambient temperature. Three ambient temperatures will be utilized: hot, moderate, and cold. The ideal temperature range for growing tomatoes are 18 – 30 °C. Moderate is the middle temperature of this range (24 °C). Hot is 4 °C above the temperature range (34 °C), and cold is 4 °C below the temperature range (14 °C).  Colonies will be randomly assigned to a temperature group, and treatment group (i.e. temperature controlled colony box or a non temperature controlled colony box). Temperature controlled, and non temperature controlled colonies, will be tested at the same time. Colonies will be tested for two weeks. During this time, recordings via the two cameras will be made 3x a day. Recordings will be 15 mins long. Each colony will therefore be recorded for 15 mins in the morning, in the afternoon, and in the evening. The recordings will be analyzed for the following: which bees are foraging and for how long, which bees are wing fanning and for how long, which bees are incubating, what temperature they achieve and for how long, and how many times bees switch between these tasks i.e. do they switch from foraging to incubating.  

In total there will be 3 colonies per grouping, i.e. temperature controlled and non-temperature controlled colony boxes, for ambient, hot, and cold environmental temperatures. A generalized linear mixed model will be performed to see if pollen consumption changed by treatment group with treatment group, ambient temperature, nest temperature, day, and colony weight as factors. Two generalized linear mixed models will be used to test whether the percentage of workers fanning or brood-incubating differs between a colony treatment groups. The response variables will be the percentage of individuals performing fanning or incubation behaviors. Explanatory factors will be the same as stated above, with bee ID added as a random factor. 

Unfortunately, due to the pandemic, most work has been significantly delayed. We were unable to do any of the proposed greenhouse work. In addition, there were  occasionally shortages of bumble bee colonies. We plan to finalize all the necessary changes and adjustments to the growth chamber in February. March will be tweaking the amount of pollen initially provided in the petri dish, ensuring the ambient temperature selected are not so extreme that no bees forage, and calibrating all electronics to work in harmony. April through November will then be running the experiments and allowing the bees to forage for two weeks. In December, analyses will be performed. January through May will be finishing up running experiments in the growth chamber and all analyses. Although only 6 months is technically needed to perform all of the growth chamber experiments, it is highly likely more delays will occur due to the pandemic, and the shortage of bee colonies available in the fall. Therefore, an excess of months to perform the growth chamber experiments is planned for. Analysis of the experiments will be performed and completed by May, including analyzing the video data, the break beam data, and the statistical tests.  

Crall, J. D., Gravish, N., Mountcastle, A. M., & Combes, S. A. (2015b). BEEtag: A Low-Cost, Image-Based Tracking System for the Study of Animal Behavior and Locomotion. PloS one, 10(9), e0136487-e0136487. doi:10.1371/journal.pone.0136487

Fauser‐Misslin, A., Sadd, B. M., Neumann, P., Sandrock, C., & Osborne, J. (2014). Influence of combined pesticide and parasite exposure on bumblebee colony traits in the laboratory. Journal of Applied Ecology, 51(2), 450-459. doi:10.1111/1365-2664.12188

Sadd, B. M. (2011). Food -Environment Mediates the Outcome of Specific Interactions Between a Bumblebee and its Trypanosome parasite. Evolution, 65(10), 2995-3001. doi:10.1111/j.1558-5646.2011.01345.x

Participation Summary

Project Outcomes

Project outcomes:

At present, it is too soon to asses impacts of the project. However, if pollination services can be improved, it could lessen the amount of colonies needed to be purchase, thus financially helping farmers. 

Knowledge Gained:

At current it is too soon into the project to comment much. However, my future direction of eventually becoming an educator have not changed. 

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.