Location: Bee Research Laboratory
Project Number: 8042-21000-290-11-I
Project Type: Interagency Reimbursable Agreement
Start Date: Oct 1, 2017
End Date: Sep 30, 2018
Honey bee viruses have been frequently reported to be associated with poor colony health and bee losses. Sacbrood virus (SBV) is the most widely distributed of all the honey bee viruses and has evolved the greatest number of variant strains circulating in bee populations around the world. Recent studies showed that A. cerana strain of SBV that causes devastating disease in Asian honey bees could cross host species barrier and cause infection in A. mellifera colonies, posing a significant risk for future honeybee emerging disease events. This collaborative project involves team members from the USDA- Agricultural Research Service (ARS) Beltsville Bee Research Laboratory and the USDA-Animal and Plant Health Inspection Service (APHIS), Plant Protection and Quarantine (PPQ). The research focuses on the epidemiological and genetic investigations of SBV infection in different geographic regions to determine the significance of differences in genome sequence to the pathology of SBV in both A. mellifera and A. cerana. This information will then be used to design bee disease control strategies such as RNA interference (RNAi) based approaches in response to emerging disease outbreaks, specifically, help to protect the USA homeland if A. cerana strains of SBV are ever introduced. The broad objective will be achieved by fulfilling the following specific research objectives: Obj- 1. Generate genomic sequences and conduct comparative genome analysis of various SBV strains associated with different epidemiological backgrounds to make evolutionary and epidemiological inferences and to develop diagnostic tests for screening various genetic variants of SBV. Obj- 2. Determine the transmission pattern of SBV in honeybees and identify factors that affect SBV transmission and survival in host populations. Obj- 3. Develop RNAi-based therapeutics against SBV by targeting the regions in the SBV genome that are refractory to mutation and evolutionarily conserved. Obj- 4. Develop novel methods to mitigate detrimental oxidative effects induced by pesticide exposure which can impair immune responses and detoxification mechanisms, rendering bees more susceptible to disease infections.
For Obj-1, SBV-infected bees from different regions where A. mellifera or A. cerana, or both, are managed for pollination services will be collected and the genomic sequences of representative SBV-infected bees associated different host species, epidemics, and disease severity will be analyzed to better understand how spatial ecology and virus evolution jointly shape epidemic dynamics of the disease. Based on the genomic information, PCR primers for detection of various genetic variants of SBV will develop for sensitive and rapid screening approaches. For Obj-2, the cross-species transmission of SBV between A. mellfera and A. cerana will be examined by purifying different strains of SBV from infected Asian honey bees and then experimentally infecting the brood and adult workers of A. mellifera by inoculation and via feeding. The degree of virulence of each A. cerana SBV strain will be determined based on the level of virus replication and the degree of pathological effects in A. mellifera. For Obj-3, dsRNA corresponding to genomic regions which are highly conserved across different strains of SBV will be generated and fed to SBV infected bees. The impacts of dsRNA on the suppression of SBV replication will be evaluated by qRT-PCR method. The phenotypic impact of RNAi treatment on overall performance of honeybees will be also evaluated. For Obj-4, food additives cyclic polysaccharides will be evaluated for their abilities as antidotes to scavenge pesticide residues in honey bees after supplementing pesticide-challenged bees with this compound. The protection of the cyclic polysaccharides conferred to bees will be assessed by measuring the transcript levels of genes encoding detoxification enzymes and immune peptides, the titers of viruses and other pathogens, and the survivorship of bee colonies.