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:
Colonies with VSH queens outcrossed to unselected commercial bees were tested in a second replication of an ARS Areawide test that involved migratory beekeeping for almond pollination in California and honey production in Montana. Populations of bees and brood, honey production and survivorship of outcrossed Varroa Sensitive Hygiene (VSH) colonies were acceptable relative to pure commercial colonies and colonies of Russian honey bees. However, populations of varroa mites increased to injurious levels, and bee populations decreased, between September and January in VSH and commercial colonies. This was a result not seen previously in VSH bees and warrants follow up investigation. A preliminary screening discovered higher titres of black queen cell virus in less populous colonies of all bee types. There is interest in further developing molecular markers associated with general hygiene. A population of bees was created by propagating inbred daughter colonies from a colony that expresses poor hygiene. Progeny of a poorly performing inbred colony will be mated to drones from colonies that express varied degrees of hygiene to make a population of mixed-genotype workers that then will be measured for hygienic activity. Two groups of bees that express differential general hygiene (high hygiene and no hygiene) will be subjected to bulk segregation analysis and fine mapping using Single nucleotide polymorphism (SNP) markers.
1. Progress was made to identify molecular markers associated with honey bee resistance to tracheal mites and varroa mites. A microarray analysis yielded 47 candidate genes related to autogrooming, a mechanism of resistance to tracheal mites. Quantitative trait loci (QTL) analysis and fine mapping yielded two candidate genes related to varroa sensitive hygiene (VSH), a mechanism for resistance to varroa mites. This initial progress provides a basis for further evaluation to identify appropriate tools for eventual marker-assisted selection of resistant bee types.
2. Technology transfer of the VSH trait is broadening varroa resistance in honey bee stocks. A test of selected Pol-line bees suggests a simple formula for commercial beekeepers to select breeders from among their own colonies that have VSH-based varroa resistance. In addition, distribution of VSH semen to breeders has furthered adoption of genetic resistance as a means of managing varroa threat.
Greenfield, M.D., Danka, R.G., Gleason, J.M., Harris, B.R., Zhou, Y. 2012. Genotype x environment interaction, environmental heterogeneity, and the lek paradox. Journal of Evolutionary Biology 25(4):601-613