Location: Bee Research Laboratory2012 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)Determine the roles of aging and stress on honey bee worker and queen longevity in order to improve overwinter survival and minimize losses to CCD.
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. A genome sequencing project for the critical honey bee pest Varroa destructor will be used to identify and validate targets for mite control, define mechanisms of mite orientation and reproduction, disrupt the ability of mites to transmit viruses, determine novel microbial control agents for this parasite, and genetic information for novel mite controls. New methods will be developed to collect, transport, purify and diagnose honey bee pathogens from the field using genetic techniques. Experimental systems for propagating and maintaining viruses and other pathogens will be used to assess virulence and host-pathogen interactions. The aging process in workers bees will be examined by exploring the physiological parameters that define long-lived bees. Specifically, research into the genetics of longevity will be undertaken along with studies using specific stressors, pesticides and resource availability to determine their role in worker life expectancy. Genetic and experimental approaches will be used to determine the impacts of pesticide exposure on the virulence and spread of honey bee pathogens. Colony level experiments will build on the work with individual bees and explore the role of the above stressors on colony overwintering and the production of long-lived winter bees, a key to understanding colony collapse disorder (CCD) as most colonies die from CCD in the fall and winter.
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 enigmatic losses, a syndrome labeled Colony Collapse Disorder (CCD). Specific focus areas in 2012 included determining the scope and impact of viral infections in honey bees and other bees important for pollination. Work showed the interplay between vectors and virulence for Deformed wing virus (DWV), the most widespread of the honey bee viruses. Two publications also documented a longitudinal study of colonies in decline, indicating that mite loads as well as levels of the gut parasite Nosema ceranae were good indicators of the risk of colony collapse. A main accomplishment for 2012 was the publication of a longterm study that defined routes of entry and impacts of the honey bee virus Deformed wing virus. This study described the latent phase of DWV, showed routes of entry and the factors that make infections lethal. DWV has emerged as a primary predictor of bee declines worldwide and understanding the mechanisms by which this virus enters bees and escapes their defenses can lead to both breeding and management changes that control disease.
1. Dynamics of Deformed wing virus. BRL scientists mapped the routes of entry of this key virus, and showed it is carried by other bee species as well as the honey bee. Avirulent infections are frequent, and the initiation of visible disease is relatively rare.
2. Causes of honey bee winter declines. By marking individual bees and analyzing them as they died, BRL scientists and Swiss collaborators showed that viral loads, mite presence and Nosema infection were strong predictors of mortality at the individual and colony level.
3. Baseline for U.S. viruses and other pathogens. BRL scientists enacted an APHIS-funded National Honey Bee survey, screening several hundred colony samples for six viruses, Nosema, and parasitic mites. The results show the state-by-state differences in viral loads, and will help in the prediction and mitigation of bee disease.
4. Host ranges of honey bee viruses. BRL scientists established that honey bee viruses are shared among bumble bees, explaining better the reservoirs of viruses in natural settings and the risks to pollinators.
5. American foulbrood disease. An excreted protease was identified as contributing to virulence by the bacterium Paenibacillus larvae, and a full effort was made to resequence the genome of the causative agent and describe complete protein sets for this species, resulting in two publications.
Chen, Y., Nakashima, N., Christian, P., Bakonyi, T., Bonning, B.C., Valles, S.M., Lightner, D. 2012. Dicistroviridae. In: King, A.M.Q., Adams, M.J., Carstens, E.B., Lefkowitz, E.J., editors. Taxonomy of Viruses. Oxford, England: Elsevier. p. 840-845.