Monitoring Colony-level Effects of Sublethal Pesticide Exposure on Honey Bees

The overall goal of these procedures is to objectively quantify honey bee colony status by using adult bee masses and brood and food resource areas to thus measure colony health in response to agrochemical exposure. This method can help answer key questions in bee science, such as colony-level effects of exposure of sublethal doses of agrochemicals to honey bees. The main advantage of this technique of this technique is that adult bee masses, brood areas, and food resources are rigorously measured rather than visually estimated and that a record is kept to double-check observations.

We have developed organizational systems to minimize the disturbance of the colony. There is a learning curve to the process that it is important to work quickly and efficiently. It is helpful to have this method demonstrated visually due to the complexity of the procedure.

Weighing the components of the hive and photographing the frames are done systematically in order to be less intrusive in the colony. Always conduct hive evaluations when ambient conditions are suitable for working with bees. To begin, place a temporary empty hive box on a flat surface next to the hive, such as on an unused hive cover so that the queen can be collected if she falls out.

Then weigh the hive lid and if present the inner cover. Next, use a spatula to remove and weigh any protein supplements or pest treatments that are resting on the frames. Keep those materials and replace them on top of the frames at the end of the evaluation.

Now note the order and orientation of all the frames by marking them with indelible ink. Then into a temporary box transfer the frames rapidly and gently in groups of two or three to retain portions of the bee cluster. Once all the frames have been moved, shake any remaining bees onto the frames in the temporary box.

Next weigh each part of the hive, including the bottom board, hive box, and entrance reducer individually. After weighing all of the parts reassemble the hive and transfer the frames back into the brood box in their original order and orientation with minimal disruption of the bees. Next, document each frame individually.

First, inspect the frame for the queen. If she is found, gently return her to the brood box. Then gently but firmly shake the worker bees off the frame and into the box.

If possible make them fall between the frames. Then photograph each side of the frame with the help of an assistant. Collect images that distinguish capped brood cells from honey cells.

Weigh the frame without the bees using a frame holder jig attached to a scale. Proceed by removing the next frame from the hive box. Again look for the queen and shake off the other bees.

If the queen is found now, place her in a part of the hive that has already been evaluated. Then return the documented frame to the box and weigh and photograph the newly removed frame. Process all the frames in this manner.

If the hive has more than one box, evaluate the lowest box first. Then when re-stacking the boxes be sure to maintain their sequence. Obtain the total hive weight during a recent period of inactivity, such as the night, or early morning on the day of the evaluation.

Calculate the adult bee mass by summing the weights of all the hive parts and then subtracting that sum from the total hive weight. The difference between the two is an estimate of the adult bee mass. Always install hive scales on a firm, level surface.

Use outdoor electronic bench scales with a capacity of 100 kilograms and are compatible with a 24 VDC indicator and a 12 bit data-logger. Next cover the scale pan with a material that will prevent excessive light reflection and heating of the hive entrance. Then calibrate the scale using weights that are at least half of the scale's maximum capacity.

Repeat this calibration periodically and always perform one when a scale is moved. For temperature sensors use thermocouples connected to a battery powered data-logger or small battery powered devices with integrated sensors and data-loggers. Protect the sensors and containers to shield them from the wax and propolis.

Attach a sensor just beneath the top bar at the center of the box. Use a short piece of wire to connect the protected sensor to the top of the frame. Staples will work.

A typical sampling regime consists of collecting three grams of wax, honey, and bee bread from at least three spots in a hive and then combining those collections into one sample. To sample wax open a 50 milliliter centrifuge tube, select a section of empty comb, and scrape the open mouth of the tube along the comb until the desired amount of max has been collected. Be sure to avoid touching the wax in the tube when capping and labeling the tube.

To sample honey or nectar, open a centrifuge tube and press mouth of the tube against the section of comb containing the honey or nectar. Allow the material to flow into the tube instead of using a scraping technique to reduce the amount of wax in the sample. To sample bee bread use a clean spatula to remove the contents of several cells containing bee bread and transfer the material into a single centrifuge tube.

To apply a treatment in syrup, pour the syrup into the feeder as rapidly as possible and take care not to spill any of it outside the hive where bees from other colonies might find it. In imageJ use the polygon tool to define the area of the frame covered with comb. Then click on analyze and select measure.

A new dialogue box will pop up that reports the number of pixels within the defined area. To define the area of the capped broods use the free hand tool to surround those cells. Then click on analyze and select measure.

If the brood pattern is not solid, due to factors such as disease, use the multi-point selection tool to count the cells instead. Each cell is about 1/4 of a square centimeter. Use the known area of the frame to convert pixels to square centimeters.

From these measurements calculate the area and percentage of the frame occupied by the brood cells. Adult bee masses were not significantly affected by exposure to both sublethal concentrations of five and 100 parts per billion. Honey bee colony growth and phenology revealed significantly lower brood production among colonies exposed to Imidacolprid at 100 parts per billion.

Hive weight data consisted of 25 hour running averages and the hourly variance from those averages. The daily amplitudes in weight change are related to foraging activity, and thus, give information about the colony's behavior. Hive temperature is reported as sine curves fit to the continuous temperature data.

The amplitudes of the curves were significantly higher in the 100 parts per billion treatment group than for five parts per billion, but neither was significantly different from the control. After watching this video you should have a good understanding of how to conduct an objective assessment of the population size and resources of a honey bee hive. Once mastered, complete hive evaluations can be done in 15 minutes or less and partial evaluation even more quickly.

While attempting this procedure it is important to work swiftly and mindfully, be careful not to bump or drop the parts of the hive containing bees. These techniques were developed to provide researchers in apiculture with a way to obtain objective data in studies that explore the impact of nutrition, agrochemical exposure, and pest treatments on colony level growth and activity.