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Research Project: Managing Diseases and Pests of Honey Bees to Improve Queen and Colony Health

Location: Bee Research Laboratory

2010 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 2010 included determining the multiple factors that 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. BRL scientists also worked on novel controls for Nosema ceranae, a parasite implicated in CCD, via a CRADA with a Cooperator and collaborations in the U.S., Thailand, and Europe. These controls focused on inhibiting Nosema by targeting metabolic proteins identified in the ARS-driven Nosema genome project. A main focus in 2010 was on genomic traits and control of the parasitic mite Varroa destructor. This species is a key pest and ongoing genomic analyses at the BRL has revealed targets in the Varroa genome for knockdown approaches using RNA inactivation and a set of mite-associated microbes that could provide novel biocontrol agents for mites. The RNAi resources are being used by at least four laboratories and one company in the USA and Europe in order to develop and improve this promising mite treatment. Microbes from Varroa are the subject of to submitted Technology Transfer efforts and one patent application. The Varroa Genome Project was supported further this year by a USDA-AFRI grant to ARS which allows a team of scientists to pursue this project and develop novel controls for mites. The BRL remains a leading laboratory for understanding the impacts of viruses on bee health. Ongoing projects showed the importance of nutrition in combating viral impacts, and pointed toward Varroa mites as an important vector of Israeli acute paralysis virus. Controlled experiments with the larval pathogen Paenibacillus larvae (cause of American foulbrood disease) revealed differential survival by bee larvae from specific AFB lineages, and a potential role for RNA inactivation for changing the bee immune response. Current work is focused on the genetic heritability of resistance traits and the environmental components that can help bees survive this and other pathogens.

4. Accomplishments
1. Causes and treatment for Colony Collapse Disorder: BRL scientists have helped lead multi-institutional efforts to understand and mitigate Colony Collapse Disorder, a phenomenon that has had large impacts on U.S. beekeeping and pollination for the past five years. A recent publication documents with the highest detail to date, that CCD is in fact caused by multiple factors, with pathogens being the most likely cause or partial cause of this syndrome, but with possible roles for both environmental chemicals such as pesticides and nutritional deficits for bees. Of particular interest in these studies were honey bee RNA viruses and the parasite Nosema ceranae. Microarray studies revealed broad changes in the RNA of bees from collapsing colonies, and it is proposed that some of these changes reflect attacks from viruses.

2. Pesticide impacts on bee health: Honey bees have proven to be susceptible to many environmental chemicals, including anthropogenic pesticides. A widespread survey of bees and hive materials from declining and healthy colonies helped reveal which chemicals bees face and allow the testing of correlations between chemical exposure and bee declines.

3. Nosema ceranae impacts: Nosema disease has long been known in honey bee colonies, but both the prevalence and inferred health impacts of Nosema 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.

4. Insect Immunity: Honey bees combat American foulbrood, viruses, and Nosema with immunity proteins found across the insects. A BRL scientist helped define those immune proteins in wasp and aphid genomes, allowing a broad comparative look at bee immunity and possible targets for breeding programs. These efforts, along with experimental studies of honey bees in the field, indicate that bee immunity is also aided by colony-level defenses including the use of protective plant resins and hygienic behaviors.

Review Publications
Evans, J.D., Spivak, M. 2009. Socialized Medicine: Individual and communal disease barriers in honey bees. Journal of Invertebrate Pathology. 103:562-572.

Simone, M., Evans, J.D., Spivak, M. 2009. Resin collection and social immunity in honey bees. Evolution. 63:3016-3022.

Gerardo, N.M., Altincicek, B., Anselme, C., Atamian, H., Barribeau, S.M., De Vos, M., Duncan, E.J., Evans, J.D., Gabaldon, T., Ghanim, M., Heddi, A., Kaloshian, I., Latorre, A., Monegat, C., Moya, A., Nakabachi, A., Parker, B.J., Perez-Brocal, V., Pignatelli, M., Rahbe, Y., Ramsey, J., Spragg, C., Tamames, J., Tamarit, D., Tamborindeguy, C., Vilcinskas, A. 2010. Immunity and defense in pea aphids, Acyrthosiphon pisum. Genome Biology. 11:R21.

Vanengelsdorp, D., Evans, J.D., Saegerman, C., Mullen, C., Haubruge, E., Nyguyen, K., Frazier, M., Frazier, J., Cox-Foster, D., Chen, Y., Underwood, R., Tarpy, D., Pettis, J.S. 2009. Colony Collapse Disorder: A descriptive study. PLoS One. 4(8):e6481.

Werren, J.H., Richards, S., Desjardins, C.A., Niehuis, O., Gadau, J., Colbourne, J.K., Elsik, C.G., Murphy, T., Worley, K.C., Zdobnov, E.M., Evans, J.D., Dang, P.M., Hunter, W.B. 2010. Functional and evolutionary insights from the genomes of three parasitoid nasonia species. Science Magazine. 327:343-348.

Chen, Y., Huang, Z.Y. 2010. Nosema ceranae, a newly identified pathogen of Apis mellifera in the U.S. and Asia. Apidologie. 41:364-374.

Evans, J.D. 2009. Host-parasite interactions: Resist or tolerate but never stop running. Review Article. 5(6)721-722.

Johnson, R., Evans, J.D., Robinson, G., Berenbaum, M. 2009. Changes in Gene Expression Relating to Colony Collapse Disorder in honey bees, Apis mellifera. Proceedings of the National Academy of Sciences. 106(35):14790-14795.

Genersch, E., Evans, J.D., Fries, I. 2009. Honey bee disease overview. Journal of Invertebrate Pathology. 103:S2-S4.

Antunez, K., Anido, M., Schlapp, G., Evans, J.D., Zunino, P. 2009. Characterization of secreted proteases of Paenibacillus larvae, potential virulence factors in honeybee larval infection. Journal of Invertebrate Pathology. 102(2):129-132.