Road Trip: How Hive Transportation Puts Stress on Honey Bees
By Dacotah Melicher, Ph.D.
When we think about going on a road trip honey bees probably don’t come to mind, but bees spend a surprising amount of time on the nation’s highways. Most of our food production by weight consists of just a few species of wind-pollinated grains, but more than 80 percent of crop species, including almost all fruits and vegetables, require some kind of pollinator. For this reason, transporting honey bees (Apis mellifera) to provide pollination for agriculture is big business. Commercial pollination services maintain thousands or even tens of thousands of hives that are available for rent, and they deliver by the truckload all over the country.
Growers have a narrow window to provide intensive pollination. Many pay commercial beekeepers to transport hives by truck to saturate their fields during the bloom. Most crops bloom during a brief, seasonal period that may be as short as couple weeks, and they need intensive pollination during this time to be profitable. Commercial pollinators can pollinate crops all over the country by taking advantage of variation in growing seasons. Hives may be moved multiple times and several thousand miles per year.
Bees have received a lot of attention recently, and for good reason. They face challenges from parasites and pathogens while demand for pollination services increases annually. The practice of transporting hives is monitored by state and federal agencies who release annual reports regarding the health, winter survival, and inventory of the nation’s honey bees. While some research focuses on transporting hives, we found very little work has been done specifically investigating the effects of the road trip on colony stress and survival.
A colony may see the sun set in North Dakota and rise in California. In the intervening time, bees are confined in their hives, loaded onto trucks, and transported long distances at highway speeds, sometimes through mountain passes on the way to the West Coast. Hives meant for pollination are often staged in bee yards until they are needed and are moved again.
In research published this week in Environmental Entomology, colleagues and I at the U.S. Department of Agriculture’s Edward T. Schafer Agricultural Research Center, in collaboration with North Dakota State University (NDSU), investigated transportation stress while bee hives are in transit to identify sources of stress that may affect survival and pollination ability. Collaborators on the study included Elisabeth Wilson and Julia Bowsher at NDSU, George Yocum and Joseph Rinehart at the USDA Agricultural Research Service, and Steve Peterson at AgPollen LLC. Through our study, we found that colonies experienced cold stress during shipping, with smaller colonies especially vulnerable.
Honey bees are one of the few insect species that can thermoregulate much higher than ambient temperatures. They do this through coordinated social behavior, and they have evolved to rely on stable, warm temperatures between 32-35 degrees Celsius (about 90-95 degrees Fahrenheit). Deviations from this range are stressful. Above this range a colony will quickly suffocate and die. Below this range, colonies often survive, at least for a time, but cold exposure in developing brood may cause developmental abnormalities. Commercial pollinators favor increased airflow because the consequences of a hive that overheats are immediate and obvious. Our research found, however, that smaller colonies lost their ability to thermoregulate the hive, and some never recovered. Smaller colonies also experienced a significant loss of population and had much lower long-term survival. Large, robust colonies maintained hive temperature and experienced less population loss.
My colleagues and I measured changes in stress response before departure, immediately after arrival, and after a two-week recovery period, using gene expression as indicators. We found that genes associated with chill stress, immune function, defense response, and methylation increased after the hives were relocated, which all decreased after the recovery period.
According to the Bee Informed Partnership, there are around 2.67 million honey bee colonies in the United States. Many of these colonies are used for agriculture, providing a vital service essential for a diverse and affordable food supply. There are many other potential sources of stress during transportation. While this study focused on cold stress, changes in barometric pressure, humidity, turbulent airflow, diesel exhaust, and vibration are also potential directions for research. Small sources of stress may have large consequences, especially if they are persistent or repeated (like noisy neighbors or trying to sleep with a mosquito in the room). Stress during transportation can be reduced with new or updated management practices, and this may have the additional benefit of allowing honey bee colonies to survive other challenges.
Dacotah Melicher, Ph.D., is computational biologist and postdoctoral assistant at the USDA Agricultural Research Service in Fargo, North Dakota, where he also experiences significant cold stress. His research focuses on development, temperature stress, and overwintering adaptations in insects, primarily but not exclusively pollinators. When not stressing out insects he enjoys hiking, cooking, and pottery. Email: firstname.lastname@example.org.