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
Microarray analyses and Quantitative Trait Loci (QTL) mapping continued on bees that differentially express the trait of autogrooming to identify genomic regions associated with tracheal mite resistance. Confirmation of putative genes with Real-Time Polymerase Chain Reaction (rtPCR) will commence when microarray data are analyzed. This work supports the goal of developing and applying Marker Assisted Selection (MAS) to identify desirable traits in potential breeding material. New information was gained about the biology underpinning the Varroa Sensitive Hygiene (VSH) trait. Reduced mite fertility in VSH colonies likely is derived from both bees targeting fertile mites and from simply uncapping (but then recapping) infested brood, resulting in disrupted reproduction. The presumed chemical cues which VSH bees target through hygiene are being sought in collaborative work with ARS chemical ecologists. Genomic analyses continue on the VSH trait. Within the unit, microarrays are being used to identify candidate genes that may regulate the trait. Ongoing collaborative activities with university and industry personnel include an “association test” to link varroa resistance with genomic single nucleotide polymorphism (SNPs), a QTL mapping project and a proteomics project. Bees phenotyped for VSH or varroa resistance were provided to collaborators for these efforts. MAS of VSH has high potential for use in enhancing varroa resistance in diverse bee stocks. Colonies with VSH queens outcrossed to commercial Italian bees performed very well in both years of a 2-year, 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 were treated with miticides to manage varroa. The goal of introgressing VSH into commercially available bees was expanded to include the best colonies from this test. The selections were propagated and transferred to a Cooperative Research and Development Agreement (CRADA) holder, who now is selling breeding material from this population.
1. Commercialization of VSH Honey Bees Selected for Pollination Performance. Honey bees are the chief pollinators of crops in the United States, but this vital agricultural service is jeopardized as colony numbers decline from major threats such as parasitic varroa mites. Bees with the trait of varroa sensitive hygiene (VSH), which have good resistance to the mites, were tested for two seasons in a commercial migratory beekeeping operation focused on crop pollination. Colonies were created from outcrossed VSH queens (that is, matings not controlled), a method used by most large-scale beekeepers. Colonies were shipped nationwide and used to pollinate almonds in California, apples in New York, low-bush blueberries in Maine and cranberries in Massachusetts, followed by late summer honey production in New York. VSH colonies performed comparatively well in terms of survival, populations of bees, and resistance to varroa mites. The best-surviving VSH colonies from each year were propagated to form a breeding population with enhanced genetics for both mite resistance and behavior related to crop pollination. These bees are now being marketed by a Cooperative Research and Development Agreement (CRADA) partner, and the germplasm should improve adoption of mite resistant bees by commercial beekeepers who pollinate crops.
Harris, J.W., Danka, R.G., Villa, J.D. 2010. Honey Bee (Hymenoptera: Apidae) with the Trait of Varroa Sensitive Hygiene Remove Brood with All Reproductive Stages of Varroa Mites (Mesostigmata: Varroidae). Annals of the Entomological Society of America. 103(2):146-152.