2008 Annual Report 1a.Objectives (from AD-416) Identify and describe traits of the honey bee that produce resistance to Varroa destructor. Combine two or more mite-resistance traits of the honey bee and determine if the traits are independent, compatible, and interactive. Develop productive bees that will provide the beekeeping industry with immediate resistance to varroa and will serve as vehicles to insert mite-resistance genes into our nationwide population of bees. 1b.Approach (from AD-416) Use traditional selective breeding and employ single-drone inseminations to find, isolate and describe traits of the honey bee that provide resistance to varroa mites. Combine the SMR trait (an established mite-resistance trait that suppresses mite reproduction) with newly developed traits and determine if the traits are independent, if they are compatible when bred into the same bee or the same colony, and if their interactions affect mite resistance. We will develop productive hybrid bees that express one or more mite-resistance traits and will evaluate these hybrids for pollination-related foraging performance to help judge their suitability as commercial pollinators. 3.Progress Report This is the final year of the project. Significant advances were made in understanding the biology of the SMR/VSH trait. Field tests showed that bees with SMR apparently removed mites from capped cells; thus, the trait was renamed varroa-sensitive hygiene (VSH). A backcross experiment showed no relationship between the VSH trait and poor brood production or low bee populations, so the trait itself apparently is the cause of poor brood production that is sometimes noted. We discovered that bees with VSH mostly target infested pupae that are 4 and 7 days postcapping; this timing suggests that VSH bees may be keying on infestations when varroa are initiating reproduction. VSH bees were found to extensively recap brood cells; recapping frequency thus has potential for use by queen breeders as a simple screening tool that correlates to the expression of VSH by a colony. Reduction of brood infestation and proportion of cells that are uncapped also were identified as having potential to be used as simple selection techniques. Important progress also occurred in the area of technology transfer. VSH germplasm was delivered via a CRADA to a commercial queen breeder (Glenn Apiaries) and has been given directly to other commercial queen producers. VSH queens for research were provided to ARS scientists and university scientists in the USA and Canada. Backcrossing genetically segregating drones with high VSH queens yielded colonies with a range of phenotypes for VSH-based varroa resistance; this suggests that traditional queen breeding can be used to enhance VSH levels in any stock of bees. A field test in Alabama demonstrated the varroa resistance and general beekeeping utility of VSH honey bees. Potential new sources of VSH were collected from existing commercial Italian bees and combined with research lines of VSH for future testing and possible release to the beekeeping industry. NP 305, Component: 2, Problem Statements: 2A.1 and 2A.2. 4.Accomplishments 1. Initial development of Italian X VSH germplasm. We sought to increase adoption of germplasm by combining bee lines having high VSH with lines of commercial Italian stock. Potential new sources of VSH were collected from existing commercial Italian bees and combined with research lines of VSH. Evaluations of this material yielded some with good beekeeping characteristics and that also had low varroa population growth. The best performing colonies are being propagated to develop a semi-closed population of VSH germplasm for future release to industry. When completed this germplasm production should improve adoption of mite resistant bees by commercial beekeepers involved in crop pollination. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statements 2A.1: Improving Honey Bee Health and 2A.2: Pollination of Crops. 2. Simplified methods of measuring the VSH trait. Simpler and faster screening methods for VSH are needed to allow interested queen breeders to select the trait from their own breeding populations. Measuring the responses of individual colonies to infested brood introduced for <24 hours showed significant differences between colonies with VSH and control colonies. Reduction of brood infestation and proportion of cells that are uncapped are useful short-term and generally reliable simple selection techniques. When refined, these techniques will enable queen producers to improve varroa resistance in a wide diversity of commercial bee stocks. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 3. The Suppressed Mite Reproduction (SMR) trait was found to be caused by removal of mite-infested brood cells by adult bees. Understanding the behavior of bees that resist varroa will help breeders to test and select for resistance. Field testing showed that bees with SMR apparently removed mites from capped cells; thus, the trait was renamed varroa-sensitive hygiene (VSH). Of the mites that remained, VSH colonies had a much higher rate of nonreproductive mites (80%) than non-VSH colonies had (29%). This suggests that VSH bees removed reproductive mites more often than they removed nonreproductive mites. By knowing the mechanism behind the VSH trait, we and other bee breeders will be better able to select for this trait and also separate this trait from other mite-resistance traits. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 4. A backcross experiment showed no relationship between the VSH trait and poor brood production or low bee populations. We and others had noticed that colonies with high levels of the VSH trait sometimes had poor brood production. The experimental results suggest that it should be possible to produce a stock that has good beekeeping qualities while it is virtually free of varroa mites. This should help allay beekeeper concerns about adopting resistant bee stocks. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 5. Backcrossing genetically segregating drones with high VSH queens yielded colonies with a range of phenotypes for VSH-based varroa resistance. Improving understanding of the biology of VSH may help breeders in testing and selection for varroa resistance. Colonies with greater frequencies of non-ovipositing mites apparently have bees with correspondingly greater numbers of genes for VSH. The range of expression showed that bees with the VSH trait did not hygienically remove mite-infested brood if the infesting mite did not reproduce. It also suggests that the easiest way to measure VSH is to measure the frequency of mites that do not lay eggs. This identifies a screening tool for use by queen breeders. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 6. Bees with VSH mostly target infested pupae that are 4 and 7 days postcapping. Improving understanding of the biology of VSH may help breeders in testing and selection for varroa resistance. This timing suggests that VSH bees may be keying on infestations when varroa are initiating reproduction. This knowledge allows more precision when researchers or beekeepers are looking for the VSH trait. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 7. A recently completed field test in Alabama demonstrated the varroa resistance and general beekeeping utility of VSH honey bees. Field studies are needed to document the utility of mite-resistant bee stocks. VSH and Russian bees developed by ARS were tested in cooperation with beekeepers in Alabama. Through three seasons of measurement, resistant stocks required less treatment against parasitic mites than the Italian-based control stock did. The total percentages of colonies needing treatment against varroa mites were 12% of VSH, 24% of Russian and 40% of control. The total percentages requiring treatment against tracheal mites were 1% of Russian, 8% of VSH and 14% of control. The overall average honey yield from Russian (59 lb) and VSH (52 lb) colonies was comparable to that from control colonies (46 lb). Beekeepers did not report any significant behavioral problems with resistant stocks. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 8. New transfer of VSH germplasm to industry via a CRADA. VSH is a breeding tool that can be used to distribute varroa resistance widely. New releases of VSH germplasm provide increased diversity of VSH breeding material for distribution as breeder queens, and so can benefit a wide array of beekeepers. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 9. Identification of extensive recapping of worker brood cells by VSH bees. Improving understanding of the biology of VSH may help breeders in testing and selection for varroa resistance. Differences between VSH and susceptible bees in the frequency of recapping of brood cells tend to be greater than differences in other measures related to mite resistance. In addition, recapping is easier to identify than other measures of mite resistance (e.g., the reproductive status of varroa). Recapping frequency thus has potential for use by queen breeders as a simple screening tool that correlates to the expression of VSH by a colony. This research addresses NP 305: Crop Production, this research falls under Component 2: Bees and Pollination, and is linked to Problem Statement 2A.1: Improving Honey Bee Health. 5.Significant Activities that Support Special Target Populations None. 6.Technology Transfer Number of Active CRADAs 1 Number of Web Sites Managed 1 Number of Newspaper Articles and Other Presentations for Non-Science Audiences 2 Number of Other Technology Transfer 1 Review Publications Harris, J.W. 2007. Bees with Varroa-Sensitive Hygiene Preferentially Remove Mite-infested Pupae Aged <5 Days Postcapping. Journal of Apicultural Research 46(3):134-139