Bumble bees are a key player for the pollination of crops such as blueberries and greenhouse tomatoes. Therefore, many beekeepers and farmers work together, using commercial bumble bee colonies to pollinate these crops. However, bringing them from one location to another may also lead to a problem: parasites and diseases can spread and even increase. In the past, this situation lead at times to increased bumble bee losses in some regions. A new study has found a specific answer to this known problem: One of the main reasons for poor bumble bee health in the US was and still is a fungus pathogen called Nosema bombi, according to results published in the Proceedings of the National Academy of Sciences (PNAS).
The study included a temporal analysis of DNA sequence variation in Nosema bombi in different geographical locations. "We used molecular techniques to screen thousands of bumble bees to track Nosema infections," said Professor Sydney Cameron, entomologist at the University of Illinois and leader of the research project. Historical evidence of infection was derived from bee specimens in natural history collections in North America and Europe. Analysis of these samples showed, in fact, that Nosema bombi was already present in the US as early as 1980. The study also found that infections in commercial bumble bee pollination operations in the 1990s coincided with infections in wild bumble bees.
Principal Scientist and Entomologist at Bayer’s Bee Care Center in North America
Dick Rogers, Principal Scientist and Entomologist at Bayer’s Bee Care Center in North America, recognizes a clear correlation: “The deployment of infected commercial colonies could spread Nosema and potentially increase infection in areas where wild bumble bees are present.” Rogers also notes that Nosema is difficult to control under mass rearing situations of bees. Therefore, “commercial production of Bombus species requires careful management and sanitation to prevent an infection with Nosema,” he adds.
Different factors can negatively impact the health of bumble bees. This new study suggests that Nosema bombi has been a key player for poor bumble bee health in the US for many years. "But we still don't know whether the fungus is becoming more virulent or the bumble bees – already stressed from habitat loss and degradation and other infections – are becoming more susceptible to Nosema," said Cameron. Investigating Nosema and other bee parasites will remain an important part of bee research.
The methods and results of the study were published in PNAS: “Test of the invasive pathogen hypothesis of bumble bee decline in North America.”
You can also read about the study in the article “Study suggests commercial bumble bee industry amplified a fungal pathogen of bees.“