Sustainable Solutions to Problems Affecting Honey Bee Health
White Paper: Honey bee genetics and breeding
As the managed pollinator of choice for numerous crops, the honey bee is an animal of substantial importance to U.S. agriculture. However, like many of the crops they pollinate, honey bees are not native to North America. Current honey bee populations within the United States reflect historical patterns of introduction from Old World source populations and the genetic consequences of founder events and subsequent queen propagation practices by beekeepers. With few exceptions, commercial queen propagation in the United States has relied on the production of a large number of saleable queens from a very limited number of queen mothers each generation. The ratio of daughter queens to queen mothers in these operations has averaged well over 1000:1 over the past decade (1, 2, 3).
Following the establishment of parasitic honey bee mites in U.S. beekeeping operations in the 1980's, substantial losses occurred at the national level to both managed honey bees and a formerly robust feral honey bee population (4). While queen production output was able to provide replacement queens for the beekeeping industry during this period, little effort was made to select for and incorporate genetic traits that enhanced the resistance of honey bees to parasitic mites and diseases. Unfortunately, substantial annual losses of honey bees due to parasitic mites have continued, as the mite Varroa destructor rapidly develops resistance to beekeeper applied chemical control measures. The inherent genetic capacity of some honey bees to tolerate or resist V. destructor, tracheal mites and contagious brood diseases is well known (5, 6, 7). However, there has not been a concerted effort within the queen breeding industry to develop selection protocols nor to manage even breeder queen populations without supplemental miticides and antibiotics. Exceptions include some private and public institution bee breeding programs that have adopted selection protocols based, in part, on specific assays, for traits of apicultural significance. While the impact of these programs has been limited, relative to overall queen production totals, collectively they represent a germplasm reserve of honey bee stocks that are comparatively productive, mite resistant and healthy in the face of known pathogens and stressors. Measurements that are used in selection protocols include the expression of hygienic behavior, short-term weight gain, mite and bee population growth, temperament, Varroa sensitive hygiene and others.
Recent reports of increased honey bee losses in the United States due to as yet undefined causes (8) makes it clear that high priority should be given to selecting and breeding honey bees that can remain healthy with minimal need for chemical inputs in the bee hive. There is preliminary evidence to suggest that selection and breeding would be an efficient and sustainable approach to deal with novel pathogens or group of pathogens, including those that may be involved in CCD (9, 10). The recent report that a virus associated with CCD is present within a population of honey bees that are currently being imported into the U.S. in massive numbers(11) brings up another aspect that must be considered together with selection and breeding regimes, the issue of honey bee source populations and importation.
Out of the 26 recognized subspecies of honey bees, only 9 are known to have been sampled and introduced into the New World (12). Currently, commercial strains (Italian, Carniolan) based on two of these subspecies predominate in managed populations in the United States, although a third strain (Caucasian) was available until quite recently. Since 2004, due to perceived/projected shortfalls in managed honey bee colonies available to effect almond pollination, the U.S. has permitted the importation of honey bees of presumptive European origin maintained in Australia. These honey bees underwent a genetic bottleneck associated with importation, similar to U.S. populations (vis a vis sampling original sources from Europe) although, in contrast to U.S. populations, the Australian honey bees have not been selected for any measure of resistance through exposure to parasitic mites over the past 20 years.
The importation of additional honey bee germplasm for selection and breeding purposes could address several key needs. First, the importation of germplasm from Old World subspecies known to have been sampled and previously introduced to the U.S. would provide additional genetic diversity for breeding purposes, a means to enhance and maintain sex allele diversity, to recover the commercial Caucasian strain and potentially bolster mite resistance. The latter contribution would depend on whether original Old World source populations (with their own history of mite exposure and survival) were utilized (13), rather than mite-free "introduced" populations from other New World sources. Secondly, the importation of novel honey bee germplasm from subspecies now known to be the original pollinator for crops of agricultural importance, such as A. m. pomonella in endemic forests of wild apples and pears, may provide improved pollination efficiency in crop-specific climatic conditions. Finally, as genetic markers associated with genetic resistance mechanisms or useful immunological or behavioral characteristics become available, Old World honey bee populations represent an available resource for marker-assisted identification of desirable germplasm. Currently, there is no explicit protocol U.S. researchers and breeders to import live bees from many countries nor are there readily accessible quarantine facilities to assist in safe importation of stocks.
In summary, research is needed to:
1) Screen available stocks of honey bees from U.S. breeding programs for the expression of genetic characteristics associated with colony health. This could involve phenotypic measurements of heritable traits or identification of specific genes that influence these traits. In addition to known apicultural traits and measures of genetic diversity, these characteristics could include immunological resistance to pathogens and potential indicators of "CCD-resistance" detectable through novel screening protocols.
2) Develop a selection and breeding protocol for the queen breeding industry that can be implemented with existing honey bee stocks to maximize the preservation of genetic diversity (sex-allele diversity) , while still permitting measurable stock improvement in areas of disease resistance and parasitic mite tolerance. Stocks identified in the colony health screening protocol (1) as useful to breeders could be promoted within this effort.
3) Characterize additional populations of Old World honey bee stocks as potential sources to assure sustainable germplasm maintenance within the U.S. bee breeding industry. This research will use molecular markers for the identification of specific subspecies and to label highly desirable breeding lines or lines expressing "CCD-resistance" (1). Develop a protocol to maintain these stocks within an association of involved university/private/government bee breeding facilities.
Primary author: Steve Sheppard1
Participants: Marla Spivak2, Greg J. Hunt3
1) Schiff, N.M. and W.S. Sheppard. 1995. Genetic analysis of commercial honey bees (Hymenoptera: Apidae) from the southern United States. J. Econ. Entomol. 88: 1216-1220.
2) Schiff, N.M. and W.S. Sheppard. 1996. Genetic differentiation in the queen breeding population of the western United States. Apidologie 27:77-86.
3) Delaney, Schiff and Sheppard. 2007. Unpublished data
4) Sanford, M. T. 2001. Introduction, spread, and economic impact of Varroa mites in North America, in; Webster T.C., Delaplane K.S. (Eds.), Mites of the honey bee, Dadant and Sons, Hamilton, Illinois, pp. 149-162.
5) Guerra Jr., J. C. V., L. S. Gonçalves and D. De Jong. 2000. Africanized honey bees (Apis mellifera L.) are more efficient at removing worker brood artificially infested with the parasitic mite Varroa jacobsonii Oudemans than are Italian bees or Italian/Africanized hybrids. Genetics and Molecular Biology 23 89-92.
6) Spivak, M. and G. S. Reuter. 2001. Resistance to American foulbrood diseases by honey bee colonies (Apis mellifera) bred for hygienic behavior. Apidologie 32: 555-565.
7) Danka, R. G. and J. D. Villa. 2000. A survey of tracheal mite resistance levels in U.S. commercial queen breeder colonies. American Bee Journal 140: 405-407.
8) Oldroyd, B. P. 2007. What's killing American honey bees? PLOS Biology, 5: 1195-1199.
9) Evans, J. D. and D. L. Lopez. 2004. Bacterial probiotics induce an immune response in the
honey bee (Hymenoptera: Apidae). J. Econ. Entomol. 97: 752-756
11) Cox-Foster et al. 2007. A metagenomic survey of microbes in honey bee colony collapse
disorder. Sciencexpress, 6 September 2007, 10.1126/science.1146498
12) Sheppard, W.S. 1989. A history of the introduction of honey bee races into the United
States, I and II. Amer. Bee J. 129: 617-619, 664-667.
13) De Guzman, L.I., T.E. Rinderer, A. M. Frake. 2007. Growth of Varroa destructor (acari:
varroidae) populations in Russian honey bee (Hymenoptera: Apidae) colonies. Ann.
