1a. Objectives (from AD-416)
Objective 1: Identify and evaluate traits, genes, and markers associated with honey bee resistance to mites and pathogens, possibly including agents discovered to cause colony collapse disorder (CCD). Objective 2: Use traditional breeding and marker-assisted selection (MAS) to develop commercially desired honey bees (other than Russian bees, which are addressed in a sister project) with resistance to parasites (e.g., mites), depredators (e.g., small hive beetle), and diseases (e.g., fungi causing chalkbrood disease), possibly including agents discovered to cause CCD. Objective 3: Develop resistance-based integrated pest management (IPM) systems for management of pests in commercially desired honey bees (other than Russian bees), particularly systems useful for early spring build up.
1b. Approach (from AD-416)
Traits that are known to confer resistance to mites (autogrooming against tracheal mites; VSH or its behavioral subtasks against varroa) will be subjected to microarray analysis to identify genes associated with specific phenotypes. Genes will be further screened for up- and down-regulation using rtPCR assays. New traits of resistance to varroa (reduced invasion by mites into brood cells; brood-mediated suppression of mite reproduction) or to CCD-related agents will be sought by measuring variation among diverse bee sources. Traditional breeding will be used to create honey bees suitable for commercial crop pollination by combining lines having high VSH with commercial stock. Molecular-marker-assisted selection will focus on genetic markers developed earlier for autogrooming and VSH. Simplified methods for queen breeders to select for VSH will be evaluated by correlating VSH expression with changes in brood nest characters during short-term exposure of infested combs. Sustainability of varroa resistance in bees used for migratory crop pollination will be determined by measuring survivability and performance of VSH colonies in cooperation with commercial beekeepers. Recommendations for resistance-based Integrated Pest Management (IPM) systems against varroa will be developed by integrating resistant bee stock with other non-chemical means to manage varroa.
3. Progress Report
Behavioral and genomic aspects of known resistance traits were detailed in FY09. Bees resistant and susceptible to tracheal mites were created, their expression of autogrooming was phenotyped, and initial microarray analysis is being performed. Genetic sources were phenotyped for VSH components for subsequent screening with microarrays and for Quantitative Trail Loci (QTL) analysis of the trait. In a collaborative “association test” to link varroa resistance with genomic SNPs, 288 colony samples were genotyped and data analysis was begun. New beneficial traits also were sought in FY09. Previous results suggested strong variation in the fecundity of varroa mites that infested different bees. A propagated generation of phenotypic extremes was screened for a brood-based suppression of varroa reproduction. Another potential varroa resistance trait is low invasion of mites into cells of host bees. Methodology was developed that permits identification of differential invasion. Infections with Nosema spp. are increasing and may contribute to CCD. A diverse group of colonies was screened for variation to Nosema infection by exposing worker bees in a naturally infected colony. A molecular assay was developed to simultaneously identify and quantify infections arising from two Nosema spp. A study of disease kinetics was conducted using the natural infection technique and molecular assay. Longevity of worker bees during winter may impact colony survival and relate to CCD. Screening diverse colonies for variation in worker lifespan showed good correlation between results of cohorts divided between standard laboratory cages and their natal hives, suggesting that variation exists and can be measured easily and accurately in cages. Breeding focused on previously screened VSH X commercial Italian colonies. These colonies were propagated, and novel germplasm was added to the population by including the best performing colonies from a year-long test of VSH colonies used in migratory pollination. Research into resistance-based Intregrated Pest Management (IPM) included refining simpler techniques to select for VSH activity. Simple, short-term measures related to VSH were found and may facilitate selection of VSH by more bee breeders. Colonies with VSH queens outcrossed to commercial Italian bees performed very well in an ARS ‘Areawide’ test of migratory crop pollination involving four crops and seven shipments of colonies. Survivorship, bee and brood populations and mite loads in VSH colonies were acceptable relative to control colonies that received miticides to manage varroa. Other colonies were established for a test of VSH queens produced by commercial queen producers, and will evaluate this end-use germplasm for response to varroa. Information gained should improve technology transfer recommendations about controlling drone sources by queen producers. Colonies of commercial and feral bees from Hawaii were established to test their response to varroa. These results should point to probable effect of varroa as the mites spread into bees on Hawaii this season, and may support a desire to import germplasm of mite resistant bees to the islands.
1. Simplified Measures of the VSH Trait of Honey Bee Resistance to Varroa. Varroa sensitive hygiene (VSH) is a trait of honey bees that supports resistance to varroa mites but is difficult for bee breeders to measure and use in a selection program. Components of VSH were evaluated to identify simple methods for selection. The responses of individual colonies was evaluated when infested brood was introduced for short periods. VSH colonies tended to uncap more infested cells after two hours, more greatly reduce mite infestation after 40 hours, and more greatly reduce infestation and mite fertility after one week. Simple, short-term measures of uncapping and of reductions in infestation and mite fertility may facilitate selection of VSH by more bee breeders.
2. Molecular Assay Developed to Detect and Quantify Two Nosema Parasites of Honey Bees. Nosema ceranae, a honey bee gut parasite relatively new to the United States, is causing increasing problems for beekeeping and may be associated with Colony Collapse Disorder.A genetic assay was developed that simultaneously detects and quantifys both N. ceranae and the longer known N. apis. The assay detects <10 copies of Nosema spp. in a single bee and may be used in place of laborious microscopic examination. The assay is being used to assess the kinetics of N. ceranae infestations during natural infection, and this information will be utilized for further study of stock and colony-level resistance to Nosema infestation and breeding for stock improvement.
Harris, J.W. 2008. Effects of brood type on Varroa-sensitive hygiene (VSH) by worker honey bees (Hymenoptera: Apidae). Annals of the Entomological Society of America 101(6):1137-1144