2013 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, 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 and 6)Determine impacts of pesticides on foragers, both acute lethal effects and sub-lethal effects on bee behavior due to chronice exposure, and develop methods to mitigate bee losses due to pesticides, including management strategies for minimizing exposure of bees to pesticides in the field.
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.
This project made several important advances relevant to National Program 305 (Crop Production), Action Plan Component II (Bees and Pollination), Problem Area A (Honey bees) over the past five years. The project coincided with the recognition of Colony Collapse Disorder as a major challenge to beekeeping and the provision of adequate pollination by honey bees. In over 50 publications, BRL scientists focused on identifying the causes of CCD and delivering management and regulatory insights to mitigate the effects of CCD. These included documented evidence that bee nutrition impacts viral disease, that viral loads were highest in colonies prone to collapse, and that Nosema ceranae had become a ubiquitous and important parasite in honey bees, all key components of Objectives 1-3 in the Plan. Genome sequences for Nosema ceranae led to the first documentation that RNA interference is a viable control strategy for this parasite. Similarly, a draft genome project for the key mite parasite of bees, Varroa destructor, gave tools for using RNA interference to control mites and for identifying weak links in mite biology that can be exploited. Colony-level surveys enabled the start of an APHIS-funded National Honey Bee Health Survey, and a baseline for disease agents, chemical exposure, and bee health across over 30 states. Integrated work showed synergies between nutrition, pesticide exposure, and parasites that are important for bee health and the maintenance of colonies. Specifically, one longterm field study showed a link between chemical exposure and levels of N. ceranae. Overall, beekeepers in the U.S. and the rest of the world were given validated insights into the causes of bee losses, new genetic tools for managing and breeding bees, and field-tested experiments aimed at improving growth and survivability of colonies in agricultural settings.
Bee responses to agricultural chemicals. BRL researchers showed significant changes in gene expression for honey bees exposed to agricultural chemicals, indicative of a physiological impact of these chemicals. Immune system genes showed altered expression in adult bees exposed to acaricides used for mite control. Both immune and detoxification genes changed in larval bees raised with sublethal levels of a range of herbicides, insecticides, and mite control agents. These results are being compared to field and laboratory morbidity trials in order to help identify risks of bees to specific chemicals. The results will lead to improved labeling and usage requirements for agricultural chemicals, protecting bees from those chemicals to which they are especially sensitive.
Interactions between honey bee disease agents and pesticides. A longterm field and experimental study pointed toward an increased susceptibility of honey bee workers toward the gut parasite Nosema ceranae after exposure to imidacloprid. The results suggest that beekeepers should be especially alert to Nosema risk following insecticide exposure, and should manage their bees accordingly.
Physiology of reproductive varroa mites. A collaborative project used genomic insights to identify the egg-yolk protein in varroa and then monitor protein production before and after female mites enter honey bee brood cells. Along with being an appropriate target for RNA interference, this protein has emerged as a crucial indicator of the readiness of female mites to commence egg-laying. It therefore provides a tool for investigations of bees that inhibit mite reproduction.
Worldwide range of bee viruses: Work determined the viruses and other microbes tied to Asian honey bee species. This work provides important insights into the resistance mechanisms of bees toward disease, and identifies for regulatory agencies those species that are at potential risk for entering the country.
Overabundance of viruses in declining colonies. In the largest survey to date of bee colonies showing signs of Colony Collapse Disorder, BRL scientists showed that such colonies carry a significantly higher diversity and load (amount of virus) than do healthy colonies. Specific viruses linked to decline include Deformed wing virus and Kashmir bee virus. The results have bearing on control methods for the problematic Colony Collapse Disorder.
Zhang, X., Chen, Y., He, S. 2012. A review of bee virology progress. Chinese Journal of Applied Entomology. 49(5):1095-1116.
Li, J., Qin, H., Wu, J., Sadd, B.M., Wang, X., Evans, J.D., Peng, W., Chen, Y. 2012. The prevalence of parasites and pathogens in Asian honeybees, Apis cerana, in China. PLoS One. 7(11):e47955.
Schwarz, R.S., Evans, J.D. 2013. Single and mixed-species trypanosome and microsporidia infections elicit distinct, ephemeral cellular and humoral immune responses in honey bees. Developmental and Comparative Immunology. 40:300-310.
Cabrera Cordon, A.R., Shirk, P.D., Duehl, A.J., Evans, J.D., Teal, P.E. 2013. Variable induction of vitellogenin genes in the varroa mite, Varroa destructor (Anderson & Trueman) by the honeybee, Apis mellifera L, host and its environment. Insect Molecular Biology. 22(1):88-103.
Cornman, R.S., Tarpy, D., Chen, Y., Jeffries, L., Lopez, D.L., Pettis, J.S., Vanengelsdorp, D., Evans, J.D. 2012. Pathogen webs in collapsing honey bee colonies. PLoS Pathogens. 7(8):e43562.