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. Objective 4: For varroa sensitive hygiene (VSH) bee stock, use molecular approaches to investigate the physiological basis for bee immune responses to fungal pathogens (such as chalkbrood), and develop strategies for controlling natural honey bee diseases. Identify molecular bases for honey bee physiological responses to chalkbrood. Identify and assess the role of genes that could potentially be involved in the antifungal activity.
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:
Final report. Behavioral and genomic aspects of previously and newly identified resistance traits of honey bees were described through the 5-year project. New information was gained about the biology underpinning the trait of Varroa sensitive hygiene (VSH) that confers resistance to Varroa mites. VSH activity is lower in drone brood than worker brood. Reduced mite fertility in VSH colonies comes as bees hygienically remove fertile mites and when they disrupt mite reproduction simply by uncapping infested brood. An initial genomic analysis of brain transcriptomes did not show a relation with known olfactory genes. DNA markers were identified in a quantitative trait loci (QTL) test and preliminarily validated in local bees. This work supports the goal of developing marker assisted selection (MAS) of desirable traits in potential breeding material. MAS-related work occurred in collaboration with university and government scientists and private beekeepers in several countries. Other significant effort on the VSH trait focused on improving use for integrated pest management (IPM) of mites and on technology transfer. IPM-related research included 1)investigating techniques to select for VSH (finding simpler methods; measuring association of hygiene against freeze-killed brood and VSH; validating repeatability of current methods); 2) measuring retention of resistance in commercial end-use queens; 3) measuring usefulness of resistance under the specific conditions faced by commercial queen producers in Hawaii; and 4) measuring functionality of bees used in stationary honey production and in migratory beekeeping operations. High performing colonies used in migratory beekeeping were selected to form an improved breeding population of VSH which has been released to the industry. Technology transfer activities for VSH included a CRADA (now an MTRA) and developing new MTAs to deliver VSH germplasm. Commercial bee breeders were instructed individually and at workshops to search for VSH in their own bees to preserve genetic diversity. New beneficial traits were sought during the project, including two traits targeting Varroa resistance. First, bees were tested and selected for brood-based suppression of mite reproduction. Selection progress has been inconsistent, and ongoing measurements of heritability will gauge whether further selection is likely to be useful. Second, differential invasion of Varroa mites into cells of bee brood was initiated and showed promise for further selection. Other research was initiated on the newly discovered pathogen Nosema ceranae; this fungal parasite may be contributing to recent abnormal bee mortality known as "colony collapse disorder". A molecular assay was developed to identify and quantify infections of two Nosema species. Field studies confirmed a negative effect of Nosema infection on bee populations within each season of the year. Selection for differential susceptibility of honey bee strains to Nosema ceranae proved difficult. Colonies selected from promising candidates in field tests were not different when tested under more controlled laboratory conditions, suggesting that improved sampling techniques are needed.