Imagine you are at a picnic on a nice sunny day. Several bees stop by buzzing around your food particularly intrigued by a bowl of fruit. Though bees may be a nuisance on this particular day, they serve an essential role in the production of much of the food we eat. They produce honey, beeswax and other products we enjoy. Bees are also crucial in pollination and without honey bees, we may not be able to enjoy fruits, nuts, and vegetables that we do today.
In the past decades, the honey bee population have declined rapidly. Between April 2015 and March 2016, beekeepers lost 44.1% of their colonies. This decline in the honey bee population could be due to many reasons including pesticides, parasites, and disease. More curiously, many colonies have fallen to colony collapse disorder (CCD), where adult worker bees die-off and surprisingly, no dead bees are found in or around the hives. The exact cause of CCD is not completely known thought many have attributed pesticides, pathogens, antibiotics, and climate change as the cause.
The honey bee microbiome
Could these declines be due to changes in the honey bee microbiome? What microbes make up the honey bee microbiome? Nancy Moran and coworkers used 16S rRNA sequencing to identify the bacterial communities within worker honey bees. Compared to the gut microbiomes of other animals, the honey bee gut microbiome is relatively simple: 95-99% of bacterial sequences retrieved from the bees belonged to only eight distinctive bacterial phylotypes.
These symbionts are essential for providing nutrients to the honey bees and for protection against invading pathogens. Work from the Moran Lab also demonstrated that one such symbiont encode genes for pectin degradation likely utilized in the breakdown of pollen walls. Other honey bee symbionts, including members of the Enterobacteriaceae, are facultative anaerobes that are involved in sugar fermentation and nitrogen metabolism needed to provide nutrients to the host (reviewed here). Clearly, any changes to these beneficial microbes will have impacts on the health of the honey bee.
The effect of pesticides on the honey bee microbiome
Bee keepers often times apply pesticides to rid the hives of parasites and other invading pests. However, in attempts to keep the hives healthy, these pesticides may also be harmful to the microbial symbionts living in the honey bee gut. By comparing honey bees from either untreated or pesticide-treated hives, researchers from Mark William’s lab at Virginia Tech found that the bacterial communities were significant altered in hives treated with pesticides. Changes such as these can mean that bees are more susceptible to disease from invading organisms or impact the bee’s nutrient intake. Accordingly, these researchers found that when the colonies were exposed to the pesticide chlorothalonil, genes for sugar metabolism decreased in the honey bee symbionts.
Not only do pesticides affect the honey bee microbiome, they can cause harm to the bees themselves and to make matters worse, pesticides do not have to be applied directly to the hive have an effect on bee populations. Thus, pesticide use on crops that honey bees may frequent can affect the bees during pollination or even eventually be brought back to the hive.