What’s the Buzz on Bee Pathogens?

US National Honey Bee Day is August 16th. Read below for a selection of papers from PLOS Pathogens on honey bee decline in the world of pathogenesis. 

This post has been modified since its original posting on August 15, 2014. 

Given the current issues affecting global health— the Ebola outbreak in West Africa, the battle to eradicate polio in Pakistan, and the rise of type 2 diabetes in the United States— honey bee health seems like it would be last on our list of worries. However, August 16, 2014 marks the 5^th US National Honey Bee Day, an organized day to raise honey bee awareness. Honey bee health and the awareness day commemorating it seem mainly geared towards the agricultural, farming, and small-scale bee-keeping communities; however, there is more interest in honey bee health from the scientific community than you may think.

The decline of honey bees is a major agricultural concern and the Agricultural Research Service (ARS), the USDA’s internal research agency, is leading several efforts to gain more information on the possible causes. The rate at which honey bee colonies are declining is alarming. According to the 2013-2014 annual survey conducted by the Bee Informed Partnership and the U.S. Department of Agriculture (USDA), total losses of managed honey bee colonies from all causes were 23.2 percent nationwide for the 2013-2014 winter. Although these losses are less than previous winters, the 2013-2014 annual survey reports that “losses still remain above the level that beekeepers consider economically sustainable.” The honey bee industry is vital to large agriculture which feeds most of the world; however National Honey Bee Day is aimed at increasing involvement from concerned citizens, most of whom are backyard gardeners and nature-loving beekeepers.

Concern for honey bee colony decline involves the scientific community as well, and actually has quite a home within pathogen research. The Bee Informed Partnership boasts a scientific advisory board composed of internationally recognized scientists to ensure that the partnership’s work is held up to high scientific standards. Furthermore, numerous PLOS Pathogens authors contribute to the honey bee cause, conducting research on various honey bee pathogens, including parasites, fungi, bacteria, and viruses. See below for some honey bee research snippets featured across the various sections of PLOS Pathogens.

Parasites

Varroa mite (Varroa destructor) is a globally distributed ectoparasite and a vector for viral pathogens of the Western honey bee.  The 2012 paper Bidirectional Transfer of RNAi between Honey Bee and Varroa destructor: Varroa Gene Silencing Reduces Varroa Population reports that Varroa gene expression can be modulated by RNA interference (RNAi) mediated by honey bees, which may potentially lead to a new conceptual approach to Varroa control. The authors fed honey bees double-stranded RNA that was then transferred cross-species, from the bee to the Varroa mite; when this was used to target and silence Varroa genes it led to substantial mite mortality.

Most recently published, On the Front Line: Quantitative Virus Dynamics in Honeybee (Apis mellifera L.) Colonies along a New Expansion Front of the Parasite Varroa destructor assesses viruses found in honey bee colonies in New Zealand in light of the country’s more recent Varroa infestation. The authors use a large-scale molecular ecology approach to study de novo Varroa infestation impact on bee colonies since Varroa was found in New Zealand within the last two decades. They studied seven honey bee viruses in both bees and mites and their data reveal that the changes in the bee virus landscape correspond to the changes in Varroa infestation.

Fungi

This Pearls article, New Models of Microsporidiosis: Infections in Zebrafish, C. elegans, and Honey Bee, covers model hosts for microsporidia, a relatively mysterious phylum of fungal-related pathogens that are often times responsible for severe diarrhea and death in AIDS patients. Apis mellifera, more commonly known as the Western honey bee, have long been known to be carriers of the microsporidian species, Nosema apis, and more recently have been increasingly found to also carry Nosema ceranae.

Delving even deeper into the microsporidian N. ceranae, Genomic Analyses of the Microsporidian Nosema ceranae, an Emergent Pathogen of Honey Bees provides genomic analysis of Nosema ceranae, comparing it to another microsporidian, Encephalitozoon cuniculi. Their comparisons provide insight into the architecture, regulation, and evolution of microsporidian genomes, and provide the first genetic tools for understanding how N. ceranae will interact with its honey bee host.

Nosema Ceranae Escapes Fumagillin Control in Honey Bees reports more closely on Nosema ceranae, the more recently discovered microsporidian first found on Asian honey bees and more recently discovered on Western honey bees. The authors compared responses of both Nosema species to fumagillin, the only antibiotic approved to combat Nosema apis-related nosema disease in honey bees, finding that N. ceranae in particular are released from the suppressive effects of fumagillin at concentrations that continue to impact honey bee physiology and that the current application protocol for fumagillin may exacerbate N. ceranae infection rather than suppress it.

Bacteria

The bacterium Paenibacillus larvae is a Gram-positive, spore-forming bacterium that is the cause of American Foulbrood (AFB), a brood disease affecting honey bee populations world-wide. Identification and Functional Analysis of the S-Layer Protein SplA of Paenibacillus larvae, the Causative Agent of American Foulbrood of Honey Bees sheds insight on the poorly-understood mechanisms behind P. larvae. Through genomic sequencing and in vitro self-assembly studies on protein complexes, the authors reveal mechanistic insight into ERIC II, the more virulent genotype of P. larvae, furthering pathogenic information on this epizootic honey bee bacterium.

Viruses

Finally, viruses also play a role in honey bee CCD, and Israeli Acute Paralysis Virus (IAPV), a single-stranded RNA virus, is reported to play a putative role. Large-Scale Field Application of RNAi Technology Reducing Israeli Acute Paralysis Virus Disease in Honey Bees (Apis mellifera, Hymenoptera: Apidae) again uses RNAi technology to feed IAPV-infected honey bees a double-stranded RNA product, Remebee-I. The authors show that treatment resulted in larger colony populations and increased honey production and provide the first successful demonstration of the use of RNAi as a preventative treatment for an insect disease on such a large scale.

A second virus affecting honey bees is Deformed Wing Virus. This Iflavirius is transmitted through the Varroa destructor parasite, causing developmental deformities and premature ageing in bee populations. The authors of A Virulent Strain of Deformed Wing Virus (DWV) of Honeybees (Apis mellifera) Prevails after Varroa destructor-Mediated, or In Vitro, Transmission exposed Varroa-naïve larvae to oral and Varroa-transmitted DWV to determine whether changes in the virus population were due to the amplification of Varroa and/or suppressing host immune responses. The authors found that a single type of virulent DWV is amplified in the pupae when transmitted via the Varroa vector, in addition to detecting changes in the immune response and developmental gene expression of the bee hosts.

Lily Berrin grew up in northern California, leaving for Los Angeles to pursue a B.A. from Occidental College in Cognitive Science (with a neuroscience emphasis) and Spanish.  After dabbling in research, she realized science communication was more her thing and landed a job at PLOS, working as a Senior Publications Assistant for PLOS Pathogens.