Project : USDA ARS

ARS Home » Southeast Area » Baton Rouge, Louisiana » Honey Bee Lab » Research » Research Project #435748

Research Project: Genetics and Breeding in Support of Honey Bee Health

Location: Honey Bee Breeding, Genetics, and Physiology Research

2019 Annual Report

Objectives
The overall goal of this research is to develop and use genetic resistance or tolerance of honey bees to biotic agents, and to devise management strategies to improve the quality of queen honey bees. This will enhance the economic value of the nation’s honey bees for pollination, honey production, overwintering and hazard resistance. Over the next five years we will focus on interrelated projects with the following objectives: Objective 1: Identify and evaluate traits, strains, and stocks for improved honey bee health, e.g., improved immunity, tolerance, or resistance to Varroa and tracheal mites, the fungi Nosema and chalkbrood, and viruses. Sub-objective 1A: Evaluate the potential for viral resistance. Sub-objective 1B: Establish and characterize genetically and functionally distinct lines that differentially respond to Nosema. Sub-objective 1C: Evaluate the potential of worker brood to suppress reproduction by Varroa. Sub-objective 1D: Determine the effect of Varroa infestations on honey bee behavior. Sub-objective 1E: Evaluate immune and stress related responses in selected honey bee stocks. Objective 2: Characterize genetic and physiological aspects of important traits, strains, and stocks and their interaction with biotic and abiotic stressors. Sub-objective 2A: Characterize the chemical ecology of VSH to aid the development of a practical selection method. Sub-objective 2B: Understand the genetic basis of Ascosphaera apis (chalkbrood) resistance observed in RHB larvae. Sub-objective 2C: Genomic sequencing of multiple stocks of honey bees. Sub-objective 2D: Differential responses to Nosema in honey bees. Objective 3: Conduct traditional and marker-assisted breeding and develop management tools for improved bees. Sub-objective 3A: Develop and use improved methods to evaluate Varroa-resistant phenotypes. Sub-objective 3B: Determine management methods using ionizing radiation to increase honey bee colony fitness. Sub-objective 3C: Evaluate autogrooming as a common resistance mechanism towards tracheal and Varroa mites. Sub-objective 3D: Use traditional and marker-assisted selection programs to improve honey bees with VSH-based resistance. Funding will be used in support of Objective 3: Conduct traditional and markerassisted breeding and develop management tools for improved bees. Objective 4: Improve knowledge of the biology, physiology, genomics, and behavior of pests (i.e. mites and the small hive beetle) that may be useful for improving their management. Sub-objective 4A: Elucidate the Nosema infection process. Sub-objective 4B: Understand effects of resistance level on Nosema infection across honey bee life stages. Sub-objective 4C: Identify new methods to limit SHB population growth in honey bee colonies.

Approach
The health and availability of honey bees (Apis mellifera) have been diminished by multiple biological problems, most notably the parasitic mite Varroa (V.) destructor. Other important threats include fungi (Nosema spp. and chalkbrood), viruses, small hive beetles and tracheal mites. Some of these interact and result in mortality described as colony collapse disorder (CCD). The major goal of this project is to mitigate these threats by finding and selecting for genetically based traits of honey bees that confer resistance to the biological problems. Scientists also will improve management techniques and describe pest biology related to control. Most research targets V. destructor. Efforts that build on our prior work with Varroa-resistant honey bees include using knowledge about Russian Honey Bees to find new traits that enhance resistance, and to improve selection methods. Honey bees with Varroa sensitive hygiene are undergoing traditional and molecular-markerassisted selection. Marker-assisted selection would be a valuable tool to overcome the difficulty of phenotyping this trait, and increase the capacity to select and breed Varroa-resistant bees. Novel traits for Varroa resistance also are being sought. New selection of honey bees will target Nosema ceranae and Deformed Wing Virus because these pathogens are thought to contribute significantly to colony losses. Research with Nosema, viruses, tracheal mites and chalkbrood will culminate in development of molecular markers for resistance factors. Management research will expand promising preliminary findings about queen and drone health associated with the irradiation of comb in mating colonies. The products of this research -- knowledge and technology -- will strengthen integrated pest management strategies for controlling honey bee pests and diseases. This in turn should lead to better profitability for beekeeping and crop pollination.

Progress Report
Research in FY 19 occurred in a bridge project between old (6050-21000-014-00D) and new Project Plans. Progress was made on four objectives and their sub-objectives, all of which fall under National Program 305, Objective 2, Bees and Pollination. Critical vacancies were filled for three scientific positions (Research Entomologist, Research Geneticist and Research Molecular Biologist) which will alleviate a significant gap in research capacity at the Unit. In Objective 1, some work targeted genetics. Analysis of the genetic diversity of seven commercial honey bee stocks found strong genetic similarity among the populations except for Pol-line bees, a stock which has undergone strong selective pressure in a breeding program. Work is ongoing to identify molecular markers related to expression of the trait of varroa sensitive hygiene, including approaches using candidate genes (in-house), whole-genome sequencing and marker discovery (in collaboration with the Institut National de la Recherche Agronomique, France) and both gene expression and sequence information via “eQTL” (in collaboration with the University of Missouri). Mite-associated viruses received significant attention. Progress was made in understanding resistance and tolerance traits associated with viral infection and how different honey bees stocks and genotypes differentially respond to Deformed wing virus, Israeli acute paralysis virus and chronic bee paralysis virus. This work involves several projects including collaborative efforts with Louisiana State University and University of North Carolina at Greensboro. The use of gamma irradiation was found to reduce levels of some viruses of bees reared in irradiated combs, but irradiated comb did not regulate Varroa populations and did not affect survival and productivity of field colonies. In Objectives 2 and 3, efforts to mitigate varroa mites are ongoing. Work began to test “social apoptosis”, or brood fragility, as a mechanism for Varroa resistance in selected stocks of honey bees. The impacts of Varroa mite parasitism on flight activities and survival of drones is being measured. Breeding for productive, Varroa resistant bees continues in a public-private partnership in which bees selected by the Unit for Varroa sensitive hygiene form much of the founding population. The chemical ecology that regulates expression of hygiene underpinning Varroa resistance is being explored with collaborators from the University of North Carolina at Greensboro, who developed a simple assay for evaluating response of bees in field colonies to chemical stimuli related to varroa sensitive hygiene. Research in collaboration with the University of Minnesota has continued to clarify the role of propolis in honey bee immunity and its potential benefits in beekeeping management, and to breed bees with improved health founded on social immunity. Some work began in anticipation of a new Project Plan. Assessment of prevalence and abundance of Acarapis woodi, Acarapis dorsalis and Acarapis externus in honey bee colonies is ongoing. Progress was also made in the discovery of feeding behavior of Tropilaelaps mites. Feeding of these mites on unsealed brood caused multiple injuries and significantly reduced survival of bees that were infested during their development. Research was initiated into the influence of honey bee genotype on the efficiency of food conversion, on a novel RNAi delivery system to mitigate honey bee pathogens, and on an alternative nutrition source for bees. Research examined various insecticide-related issues. Investigations began into substrates that can be used as reliable surrogates of insecticide detoxification by esterases, and the relationship of esterase activity inhibition on insecticide toxicity. Baseline data were established for a nationwide assessment of the resistance of Varroa mites to amitraz in commercial beekeeping operations. In a subordinate project, research was initiated on the influence of propolis deposition on insecticide sensitivity and detoxification activity in honey bees. Various insecticides were evaluated for selective toxicity to small hive beetles. Two longitudinal field trials of two years each are yielding information about the biotic and abiotic health threats to honey bees in commercial beekeeping operations. These trials were conducted in collaboration with Louisiana State University. Progress was made in collaboration with North Carolina State University and University of Pennsylvania to clarify the genetic determinants of queen quality. Protocols were established for laboratory rearing of honey bees from vitrified honey bee embryos.

Accomplishments
1. Determination of non-target impacts of insecticides on honey bees. The potential health threat posed by insecticides to honey bees is of wide concern, but insecticides are vitally needed for some pest-control programs. ARS researchers at Baton Rouge, Louisiana, determined that insecticides used by mosquito control professionals pose little harm to honey bees when applied properly under field conditions. They also determined that a miticide used to control the major honey bee parasite, the Varroa mite, did not increase the sensitivity of honey bees to several insecticides when evaluated at the colony level, and miticide use did lead to higher colony survival by controlling Varroa mite populations. The research results can be used by beekeepers to manage their colonies to minimize any potential impacts of pesticides.

2. Larval diet affects insecticide sensitivity in adult honey bees. Honey bees face threats to their health and survival. Two major environmental influences that potentially impact bee health are inadequate availability of food, and exposure to insecticides. ARS researchers at Baton Rouge, Louisiana, showed that larval bees that are stressed by a lack of pollen (the protein source for bees) respond poorly as adults when they are exposed to a neonicitinoid insecticide. In addition, the test showed that supplementing bees with a protein source helped colonies respond better to stress from insecticide exposure. These results suggest that beekeepers can improve colony health during times of poor pollen availability by feeding locally collected pollen.

3. Relative contributions of bees to pollination of rabbiteye blueberries. Rabbiteye blueberries are an important crop grown in the southeastern United States, and require adequate pollination for good fruit production. ARS researchers at Baton Rouge, Louisiana, and Poplarville, Mississippi, examined which bee species were most useful as pollinators during three years of observations. Honey bees were the most abundant pollinator each year. They increased production, but only in the largest fields where other bees were scarce. The southeastern blueberry bee was the most effective pollinator overall but was found inconsistently across fields. Other bees were not significant contributors to pollination. These findings can help blueberry growers by providing methods to assess the foraging activity of pollinators, which would provide information useful when making decisions about trying to enhance pollination services by either adding colonies of honey bees or by promoting native populations of wild bee species.

4. Gamma irradiation shows only subtle effects against honey bee pathogens. Gamma irradiation sometimes is used to inactivate bee-infectious microbes on beeswax combs. ARS researchers at Baton Rouge, Louisiana, evaluated the potential benefits on honey bee colony productivity when combs were irradiated. Production of bees and brood was not substantially improved by comb irradiation. Although levels of some common bee viruses were reduced by gamma irradiation, most were not. The use of genetically improved mite-resistant stock was more helpful than gamma irradiation in regulating mite and virus levels. Overall, the benefit from irradiating comb to improve honey bee health and colony survival was not strong. Beekeepers can use this information to inform disease-management decisions.

U.S. DEPARTMENT OF AGRICULTURE

Honey Bee Breeding, Genetics, and Physiology Research: Baton Rouge, LA