The Curious Beekeeper
Going the Distance: Scientific Bee Studies
That Make an Impact
by TIMOTHY J. BROWN and SUSAN E. KEGLEY, PhD
Pesticide Research Institute
Carefully designed scientific bee studies are invaluable tools for the practicing beekeeper. Without them it is nearly impossible to analyze the effects of different stressors on long-term colony health and make meaningful, informed decisions. In our previous installment of The Curious Beekeeper we discussed a series of flawed studies analyzing the effects of honey bee exposure to the new neonicotinoid insecticide sulfoxaflor.1 Some of the experiments designed to better understand the effects of sulfoxaflor exposure on brood development failed to follow a complete brood cycle. In addition, one of the key studies used a control hive (no exposure to sulfoxaflor) that was infested with Varroa to make comparisons against mite-free hives exposed to sulfoxaflor. Because the two colonies were not comparable in terms of mite infestation status, it was therefore impossible to draw any conclusions regarding the effect of sulfoxaflor on brood development from these experiments.
For this fourth article in our series, we counter our previous example with a study that goes the distance, with procedurally sound experiments that lead to defensible conclusions. Here we dissect the experimental design and evaluate the results from a notable 2012 study co-authored by Joseph Riddle and his colleagues at Michigan State University (MSU), Jeff Pettis at USDA, and Xianbing Xie from Nanching University analyzing the effects of long distance transport on the physiology of honey bees.2 As the first investigation of its kind, the study was designed to evaluate the two extremes in the level of transport, where one group of bees was transported while a comparison group (the negative control) was not moved at all.
The researchers’ hypothesis was that either due to higher mortality of older bees during and after transportation or due to inadequate pollen consumption by young bees, there should be measureable differences between bees that traveled and those that didn’t in terms of premature aging and ability to nurse brood. They chose to evaluate the following physiological parameters in colonies that were transported versus those that stayed in one location:
Levels of juvenile hormone (JH), which are normally low in young nurse bees, but high in foragers nearing the end of their lives. Levels of JH provide a yardstick to estimate premature aging in response to stress.
The size of the acini in the hypopharyngeal gland (HPG), used by the nurse bees to make royal jelly that is fed to larvae early in their development and also to the adult queen, drones, and foragers. The size of the HPG is related to how much food a nurse bee can produce and is genetically determined, but also age-dependent.
Protein content in head and thorax, which provides a measure of whether or not bees are getting enough protein to eat while they are being transported or if their digestion is affected by transportation.
Fat content in abdomen, another indicator of premature aging. Bees that are ready to forage generally have low levels of fat in the abdomen, while nurse bees have high levels.
Nurse bees use their hypopharyngeal (HPG) glands to produce royal jelly to feed brood. The study evaluated the effect of transportation on the size of the HPG glands. Photo credits: Left, James D. Bull; Right, Maryann Frazier.
If transportation were having adverse effects on the bees, the researchers hypothesized that bees that were transported should have higher levels of JH, smaller HPGs, lower protein content in heads and thorax, and lower lipid content in abdomen. So the challenge was to design a study to minimize the effects of other potential factors that might make it difficult to reliably compare the two groups.
Quality Control and Experimental Design
Scientific studies that present the most compelling results are typically designed to assess an outcome, while systematically changing a single variable at a time. This study on hive transport used a number of techniques to ensure they were comparing apples to apples, instead of apples to pineapples.
Because the measured parameters change with the age of the bee, it was first necessary to ensure that the comparison between the group that traveled and the group that did not was only between bees of the same age. The scientists did this by collecting newly emerged worker bees and labeling them with Testor’s color paint so they could easily find them again to make the measurements after the bees were transported. Labeling newly emerged worker bees helped the researchers ensure they were comparing only bees of the same age. Photo credit: Christofer Bang.
The strain of bee (Italians vs ....