A few years ago, scientists monitoring insect populations began to sound the alarm that honey bees, a critical player in how plants reproduce, were disappearing in ever larger numbers. In the past year, beekeepers lost 40 percent of their colonies, and entomologists were also seeing alarming losses in wild colonies around the country.
Once the numbers were quantified, the next step was to figure out why honey bees were dying off. With a grant from the US Department of Agriculture’s Agriculture and Food Research Initiative, researchers from North Carolina State University studied 39 bee colonies—about one third of them wild, or “feral”—in Raleigh, the city’s suburbs, and the countryside outside the city’s edges. Researchers examined worker bees from these colonies to assess what pathogens they were exposed to as well as how the bees’ immune system responded when triggered.
The results, published last week in the open-access journal PLOS-One, showed that honey bees lead a much healthier life in the countryside. While the immune system response did not vary by location, the pathogen load did. Honey bees in urban and suburban colonies had a larger pathogen load—more exposure to bacteria and viruses—than their country cousins. Immune system responses differed between feral and managed colonies however, with bees from feral colonies having a much stronger immune response.
The corresponding author on the paper, David Tarpy, a professor of entomology at NC State, and his colleagues identified a number of urban stresses that could produce the increased pathogen load: a limited number of food sources, higher population densities, and the higher temperatures found in municipal areas.
“Honey bees are important pollinators and play a significant role in our ecosystems and our economy,” noted Tarpy. “This work is really only a starting point. Now that we know what’s happening, the next step is to begin work on understanding why it is happening and if the same negative effects of urbanization are hurting solitary, native bee species that are presumably more sensitive to their local environment.”