2007 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.
Honey bees are vital to US agriculture because of their value as pollinators of important crops such as almonds, apples, and squash. Honey has less economic value than the billions of dollars attributed to pollination activities by bees, yet honey provides the major source of income for most beekeepers. Both pollination and honey production require healthy colonies of bees, and honey bee populations in the USA are under constant attack by Varroa destructor, an external parasite of the honey bee. This parasite is the number one problem in the beekeeping industry in the USA and worldwide. Until the late 1960’s, this mite was restricted to Southeast Asia as a parasite of Apis cerana, the Asian hive bee. It now has worldwide distribution. If a susceptible colony of bees is not protected with miticide, it dies within two years. Because of chemical contamination issues, cost of treating with miticides, and the ability of these mites to develop resistance to miticides, our long-term solution is to breed honey bees for resistance to varroa. The primary goal of this research is to control the parasitic mite (Varroa destructor) by breeding honey bees for resistance. Our approaches to this problem are as follows:
1. Continue work with suppressing mite reproduction, the SMR trait. Note: New knowledge of the details of this trait has resulted in renaming in 2005 as “varroa sensitive hygiene” (VSH) To improve breeding strategies, we will (1) determine how many genes are involved in the VSH trait (our preliminary data suggest that there are two), (2) determine if the VSH trait is associated with other characteristics of bees, (3) establish the VSH trait into inbred lines, and (4) combine these inbred lines into productive hybrids that are virtually free of mites.
2. Complement the VSH trait by developing another varroa-resistance trait, percent mites in brood (PMIB). Although we have demonstrated that we can achieve almost total resistance to varroa mites with only the VSH trait, it is not prudent to rely on one mechanism for mite resistance. PMIB is the percentage of a mite population that resides in brood cells. The remaining mites in a bee colony are phoretic on adult bees. Although this trait has been associated with lower mite populations and we have already shown it to be a heritable trait of the honey bee, it has not been subjected to selective breeding. Our goal is to select bees for low PMIB and thereby prolong the time that a mite spends on adult bees. Our approach is to isolate, intensify, and evaluate PMIB or possibly another mite-resistance trait that affects mites outside the brood cell.
Most significant--A recently completed field test in Alabama demonstrated the varroa resistance and general beekeeping utility of varroa sensitive hygiene (VSH) honey bees. Mite-resistant VSH and Russian bees developed by ARS were tested in beekeeping operations 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.
Other significant--Identification of extensive recapping of worker brood cells by VSH bees. 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.
New transfer of VSH germplasm to industry via a CRADA. New releases of VSH germplasm provides increased diversity of VSH breeding material for distribution as breeder queens.
5.Significant Activities that Support Special Target Populations
|Number of new CRADAs and MTAs||1|
|Number of active CRADAs and MTAs||1|
|Number of non-peer reviewed presentations and proceedings||9|
|Number of newspaper articles and other presentations for non-science audiences||3|
Villegas, A.J., Villa, J.D. 2006. Uncapping of sealed worker brood by european bees as responses to infestation by varroa destructor and to activity by galleria mellonella. Journal of Apicultural Research 45(4):203-206