Photo 1. Forager bees returning with fresh pollen

As part of the COMB (Conventional and Organic Management of Bees) project, where we are looking at honey bee pathogens and immune gene expression, we are also investigating another important aspect of colony health: the communities of the microbiota in honey bee guts and bee bread. Bee bread is fermented pollen that has been collected by foragers (photo 1) and packed into comb cells with layers of saliva and nectar (Photo 2). Newly emerged worker bees, less than 8 days old, eat the bee bread as a source of protein. Nurse bees also convert bee bread into royal and worker jelly as food for the larvae. However, bee bread is not sterile. It contains many microscopic fungi and bacteria (also known as a microbiome) that facilitate the fermentation process of the bee bread. Therefore, this microbiome has been shown to help preserve the stored bee bread.

Photo 2. Bee bread found in the cells within the colony.

Pollen and nectar exposed to pesticides or in-hive chemicals applied by beekeepers can change the microbiota associated with honey bee colonies (Kakumanu et al., 2016; Yoder et al., 2013). There are two potential mechanisms by which pesticides can compromise bee health through microbial interactions. First, by changing the community composition of symbionts present in bee guts—also called dysbiosis—pesticides can impact the immune system and fitness of the host. A second potential mechanism linking pesticides and bee health through microbiomes involves the impact that these chemicals can have on beneficial microbes associated with bee bread. Beneficial bacteria and fungi help with the production of bee bread by fermentation of the pollen stored in cells (Vasquez and Olofsson, 2009). In honey bees, colonies exposed to pollen contaminated with fungicides show a lower presence of beneficial fungi and higher prevalence of the pathogenic fungal disease chalkbrood. The evidence suggests that changes in the microbial communities in the bees’ gut and their food can be directly linked to honey bee colony health. Here is a great website that describes the Hidden World of Microbiomes.

Photo 3. A recently emerged bee looking for proteinaceous bee bread; they are easily identified by their wet appearance.

As part of COMB, we are comparing the species of bacteria and fungi that are found in bee bread from colonies in different management systems. This past July and August we sampled bee bread from COMB colonies in central and eastern PA and one site in West Virginia. In addition to the bee bread, we sampled 5-day-old bees in order to compare the microbiota of nurse bees in these colonies (photo 3). Bee bread and nurse bees were sampled both before and after treating the colonies for varroa mites. Different treatments were applied in each management system according to the protocol developed for each management system. Research into the microbiome of colonies is still a developing field, but knowing if different miticides change the microbiome will enable us to better understand their impact on honey bee colony health. 

The bee bread project is a collaboration between COMB and  Dr. Rob Dunn and Dr. Anne Madden from North Carolina State University.


Robyn Underwood
Parry Kietzman
Brooke Lawrence


Kakumanu ML, Reeves AM, Anderson TD, Rodrigues RR, Williams MA (2016) Honey bee gut microbiome is altered by in-hive pesticide exposures. Frontiers in Microbiology, 7:1255. DOI: 10.3389/fmicb.2016.01255.

Vásquez A, Olofsson TC (2009) The lactic acid bacteria involved in the production of bee pollen and bee bread. Journal of Apicultural Research and Bee World, 48(3): 189-195. DOI: 10.3896/IBRA.

Yoder JA, Jajak AJ, Rosselot AE, Smith TJ, Yerke MC, Sammataro D (2013) Fungicide contamination reduces beneficial fungi in bee bread based on an area-wide field study in honey bee, Apis mellifera. Journal of Toxicology and Environmental Health, Part A, 76: 587–600. DOI: 10.1080/15287394.2013.798846.

The Hidden World of Micrbiomes, link