Location: Bee Research Laboratory2009 Annual Report
1a. Objectives (from AD-416)
The central theme of this project is to reduce the impacts of pests and pathogens on honey bees using approaches ranging from field experiments to controlled pathology experiments and modern genetic and genomic applications. Specific objectives are to 1) Improve screening and management methods used by beekeepers to minimize losses due to Varroa mites and other stress factors, focusing on queen supersedure, worker longevity, and catastrophic losses such as colony collapse disorder, 2) Measure the individual and combined impacts of key honey bee disease agents including Varroa, viruses, Nosema, and the American foulbrood bacterium under field, cage, and laboratory conditions, 3) Define the resistance mechanisms of bees toward pathogens, especially bacteria and viruses, focusing on individual and group defenses as a means of providing candidate traits for breeding programs, 4) Develop and improve collection, culture and expression systems for continuous production of disease-causing pathogens in order to provide ready source experimental material and disease reproduction models for in vitro and in vivo assessments of pathogenesis and host-pathogen interactions of honey bees and 5)Explore honey bee longevity by determining the physiological parameters in workers that lead to or affect aging and defining colony conditions/stressors that impact worker longevity.
1b. Approach (from AD-416)
Developing and adult bees will be exposed to incidental pesticides, and to acaricides used to control Varroa mites, in order to determine the vulnerabilities of bees to these chemicals. A central goal will be to determine and validate methods for remediating honey bee comb containing potentially dangerous levels of chemicals or pathogens. Impacts of two species of Nosema on queen supersedure rates, worker mortality, and colony declines will be studied using controlled cage experiments and field treatments with the Nosema control fumagillin. These experiments will be followed by microscopic and genetic tests of Nosema loads, and tests of honey bee immune responses and resistance to Nosema. Activity levels of honey bee immune genes and genes related to chemical stress can be indicators of resistance mechanisms present in some bee lines, and can help test the impacts on bees of specific management techniques. Resistance to American foulbrood disease will be determined by screening lines of bees that survive controlled infection to the bacterial cause of this disease. In addition, new techniques for silencing honey bee and/or bacterial genes will be used to determine new avenues for controlling this important disease. Work on viral pathogens of bees will focus on developing controlled genetic assays for diverse viral species in bees, determining specific virulence factors in these viruses, and determining the efficacy of gene silencing and other resistance mechanisms used by honey bees to resist viral disease. Viral research will also focus on transmission mechanisms of viruses, in anticipation of determining the most economical means for reducing the impacts of direct or indirect (e.g., Varroa mite) transmission of bee viruses.
3. Progress Report
Honey bee colonies are threatened by numerous parasites, pathogens, and pests, including Varroa and tracheal mites, bacterial diseases like American foulbrood (AFB) and an assortment of bee viruses, all of which affect colony well being. The industry is also impacted by nutritional and chemical stresses placed on honey bees. In the past few years, domesticated honey bee colonies have suffered alarming and enitgmatic losses, a syndrome labeled Colony Collapse Disorder (CCD). Using a combination of chemical, cultural and genetic methods, the Bee Research Laboratory (BRL) is investigating CCD and other threats and developing integrated management and breeding strategies to deal with them in a safe and environmentally acceptable manner. The research resulting from these efforts has been disseminated to state and federal regulators, stakeholders, and other researchers via presentations, diagnostic reports, and publications in trade and research journals. Specific focus areas in 2009 included determining how multiple factors contribute to honey bee colony losses, and developing improved assays for predicting bee health risks. These efforts involved pathogens and parasites, stress on managed bee colonies, and the impacts of pesticides and other environmental chemicals. A second focus was on the emergent parasite Nosema ceranae, and successes included the first full pathological analysis of this organism, confirmation of a long history in the U.S., and a complete, annotated, genome sequence. These resources provide a definitive look at traits of this parasite and offer insights into novel control methods and tools for determining Nosema virulence and honey bee resistance mechanisms. The BRL remains a leading laboratory for understanding the impacts of viruses on bee health, and has contributed timely diagnoses and genetic analyses of viruses implicated in disease, while maintaining long-term research on virulence and resistance toward viruses, bacteria, and other bee pests.
1. Pathology and spread of Nosema disease. There has been a great increase in both the range and prevalence of Nosema ceranae, a fungal parasite of honey bees that was only diagnosed in U.S. bees in the past two years. BRL scientists established that this species has in fact been present for over a decade in the U.S. and carried out the first pathological analyses of this parasite. The latter study showed that N. ceranae is much more invasive in the body of honey bees than is the better known Nosema apis, moving and reproducing well beyond the gut wall. These projects were important for predicting the role of Nosema in Colony Collapse Disorder (CCD) and suggest different vulnerabilities of the two Nosema species to environmental conditions and to the single registered product now available for their control, fumagillin.
2. Sequencing and analysis of the Nosema ceranae genome. Nosema disease has long been known in Honey bee colonies, but both the prevalence and inferred health impacts of this disease have increased dramatically in the past few years. To better understand how Nosema affects bees, and to provide insights and tools for industry and researchers seeking to minimize Nosema disease, we led a collaborative project to sequence and describe the genome of N. ceranae. We revealed a compact genome, with a partial protein set that is complemented by proteins borrowed from their honey bee hosts. We described many features of the Nosema genome that can be exploited for chemical and genetic control strategies and provided novel markers for determining and restricting movement patterns this disease agent.
3. Small hive beetle as a pest and vector. The small hive beetle (SHB) is a parasite and scavenger of Honey bee colonies. Because SHBs feed and move in Honey bee colonies, they have the potential to act as a vector to transmit pathogens from infected bees to healthy bees. BRL scientists supervised graduate student and postdoctoral fellow from University of Bern, Switzerland, to conduct experiments to determine the ability of SHB to transmit pathogens including viruses and the spore-forming bacterium Paenibacillus larvae. The results demonstrated that SHB could be infected with honeybee viruses and American foulbrood (AFB) spores via food-borne transmission and that this beetles has the potential to act as a biological vector for transmission of honey bee pathogens. This research adds additional importance to the control of SHB and predicts the co-occurrence of multiple diseases with heavy SHB loads.
4. Assessment of interacting factors linked to honey bee colony collapse. The BRL has led efforts to expand the search for suspects in the wide-scale loss of adult worker bees in U.S. Honey bee populations, including Colony Collapse Disorder (CCD). Recent results include evidence that multiple viruses are associated with CCD, and that some collapsed colonies carry unusual traits including ‘entombed’ pollen. Ongoing work is testing for links between chemical exposure and how this exposure impacts the effects of known parasites and pathogens. CCD is now believed to have multiple causes, and the work of the BRL has helped identify those agents that are most important in this syndrome.
5. Significant Activities that Support Special Target Populations
A Bee Research Laboratory scientist has an ongoing collaboration with a professor at Howard University on Honey bee cell culture development.
Chen, Y., Evans, J.D., Zhou, L., Boncristiani Jr, H.F., Kimura, K., Xiao, T., Litkowski, A.M., Pettis, J.S. 2009. Asymmetrical Coexistence of Nosema ceranae and N. apis in Honey Bees. Journal of Invertebrate Pathology. 101:204-209.