Stressors Affecting Bees

The NAPPC Honey Bee Health Task Force
The North American Pollinator Protection Campaign (NAPPC) is a collaborative group of scientists, government agencies, NGO’s, private industries and agricultural and environmental concerns that work together to bring the plight of pollinators to national attention and to be the most trusted resource for information and behaviors in support of pollinating animals and the plants with which they interact.  NAPPC works for all species of pollinators across the whole of North America.  NAPPC partners have formed specialist task forces to address all the issues that face pollinators, and one such group is the NAPPC Honey Bee Health Task Force.

The NAPPC Honey Bee Task Force has several functions, determining each year the recipients of honey bee health grants that have for the past four years supported research in honey bee genetics, pesticide exposure, nutrition and management.  In addition, the task force is dedicated to providing the latest findings and perspectives on honey bee health to the public, policy makers and the press.  The following honey bee health issues have been provided by that task force.  We hope you find them useful, and we welcome questions and comments to

Honey Bee Health
So much of our agricultural productivity is dependent on the European honey bee (Apris mellifera) that it is no wonder that our attention is drawn to their plight.  When the honey bee suffers, so does agriculture, and so, potentially do all who depend on the bounty that comes from animal pollinated angiosperms, the flowering plants from which we derive many of our most delicious and health-giving fruits and vegetables.

While honey bees are clearly not the only hard working pollinators that deliver a bounty to humans and other animals, their recent deaths from Colony Collapse Disorder (CCD) starting in 2006 have captured the world’s attention.  To date, CCD has been defined as a series of symptoms, but the cause and the cure have remained complex and elusive.  CCD is not the only problem facing honey bees; in fact, in 2010 the overwintering losses were at the same unsustainable rates of over 30% but the cause seemed to be less from CCD than from other problems.  Below is a list of the variety of issues facing honey bees.

The North American Pollinator Protection Campaign Scientists Report on Honey Bee Stressors

The Varroa mite (Varroa destructor)

Is an external parasite that has spread from its original host, the Asian honey bee Apis cerana, to nearly all Western honey bees (Apis mellifera) worldwide. Virtually all European honey bees are highly vulnerable to Varroa mites, although some honey bee strains (VSH, Russians) show partial resistance to the mites. This mite weakens honey bees by sucking hemolymph (“blood”) from its host and by transmitting bee pathogens. A female mite reproduces by invading the cell of a bee larva just before capping. Once inside, the female lays eggs to produce offspring that feed together on the developing bee. The mother mite and her adult daughters emerge from the cell with the young adult bee host. Eventually, at high infestation rates, the mites overwhelm and kill the host colony. Beekeepers control Varroa mite populations by monitoring mite infestation rates and applying chemical treatments when mite populations become too large. Due to increased concerns over the effects of miticides on bees and mite resistance to commercial miticides, researchers are developing alternative approaches (“softer” chemical treatments, the genetics of mite resistance in honey bees, mite pheromones and hormones, and physical treatments) to control this mite.

Nosema ceranae
This microscopic fungus can weaken or even kill colonies when the majority of workers become infected. Spores of the fungus survive on wax combs and stored food inside colonies. When workers eat these spores the fungus invades the lining of the intestine. Highly infected bees cannot digest efficiently and die earlier. Beekeepers use antibiotics and disinfection of hives to control this disease.
Thus far, more than 20 honey bee viruses have been identified.  These viruses can impact bees in multiple ways, including killing developing larvae and pupae, decreasing the lifespan of adult bees, causing spasms and tremors, reducing cognitive skills, and impairing wing development so that bees cannot fly.  Most honey bee colonies have multiple viruses, and the levels of these viruses can fluctuate throughout the year.  Exposure to other stressors, particularly Varroa parasitization, can immunosuppress bees so that the effects of the viruses are more dramatic.  The only treatment for viruses thus far is to feed the colony a solution of virus-specific RNA that enhances the bees' immune responses to these particular viruses, but these treatments only suppress the viral infections, and do not eradicate them.  Other approaches that are being investigated include breeding bees with genetic resistance to the viruses.
Bacterial Diseases:
American foulbrood (Paenibacillus larvae)

American foulbrood is an infection that kills young bees (brood) inside the wax cells in which they develop. This dead brood becomes a source of infection spread by workers nursing young brood. Some bees can detect and remove the diseased brood and this stops the disease from spreading. Beekeepers also use antibiotics to prevent the disease.
Pesticides are usually man made chemicals designed to kill pest organisms, that may injure plants or animals including humans. Pests cause economic damage by reducing crop yields directly or by producing crop, or ornamental plant diseases, or by competing with crops, or by reducing animal and human health, or by damaging buildings and structures. Pesticides are categorized according to their intended use as well as by their chemical composition. Pesticides are widely used and are divided into insecticides/acaricides, used to control insects and mites or ticks, fungicides used to control plant diseases; rodenticides, used to control rodents; and herbicides used to prevent weeds from competing with crops, grasses or ornamental plants. Pesticides usually contain an active ingredient, with a known mechanism for killing the target pests. Pesticides vary widely in their safety to humans and the environment and are sold as a formulation with added ingredients that augment the action of the active material when mixed in water for application. More than 1200 chemicals are registered for use in the United States and are used in some 18,000 separate products sold under a variety of trade names. People who apply the more toxic pesticides must have training and a state issued license to use these materials.
Some insecticides have warnings or bee hazards on their label because they are toxic to honey bees, causing honey bee deaths. If the insecticide has a sub-lethal affect on honey bees it may result in reduced larval survival, altered foraging behavior or shortened lifespan of adult bees. The extent of the sub-lethal affects is still unknown.
Honey bee colonies are healthier and stronger with access to pollen from diverse sources of flowering plants. However, floral diversity in landscapes has been reduced by intensive agriculture (single crops, few flowering weeds, limited hedgerows) and urbanization. In recent years, the pollination of early crops (such as almonds in California in February) has further increased the demand for strong colonies at times of year with few floral sources. Furthermore, changes in climate patterns may also affect seasonal availability of flowering plants. This requires beekeepers to use artificial sources (sugar syrup, corn syrup, and pollen substitutes) to try to meet the increased nutritional demands of their colonies. Varroa mites
Honey bee colonies are headed by a single queen who mates with an average of 12 males, and thus honey bee colonies are extremely genetically diverse.  Several studies have demonstrated that genetic diversity improves the disease resistance and productivity of colonies, including their overwintering ability.  Furthermore, strains of honey bees can have different traits - some forage for more pollen, while others are more adept at hygienic behavior, in which diseased or parasitized brood is removed.  Several breeding programs are underway to develop stocks of bees that are more resistance to diseases and parasites, are better at overwintering in specific climates, and are productive and gentle.
Queen Quality:
The honey bee queen is responsible for producing all the workers in the colony, and she lays up to 1500 eggs a day. Poor quality queens can severely impact colony health. Queens with low egg-laying capacity can limit the numbers of health workers produced, while unhealthy queens can die or be killed by workers, causing a break in brood rearing that again limits colony growth and productivity. Poor quality queens are consistently cited by beekeepers as a major factor underlying colony failure, and a longitudinal study of colonies indicated that loss of a queen or lack of laying by a queen was one of the two factors linked to colony loss. Several factors seems to impact queen quality, including rearing conditions and mating number.
Proper management of honey bee colonies is a critical component of their health and productivity. Many of the stressors listed on this page can be mitigated by using the proper techniques. Beekeepers need to place their colonies is appropriate locations, which allow access to adequate foraging sites and are distant from areas where pesticides are being applied (honey bees can forage up to 5 km away from their colonies). Beekeepers can provide supplementary nutrition, in the form of sucrose solution or protein patties, during periods of low nectar flow. Beekeepers can monitor for pests, such as Varroa mites and Nosema microporidia, and use chemical or non-chemical methods to control these as needed. Beekeepers can minimize exposure to pathogens, such as viruses and bacteria, by systematically replacing used brood comb with fresh comb. Using genetic stocks of bees that more resistant to pests and pathogens is also an excellent way to reduce complications from these two stressors. Finally, rapid supercedure of poor quality queen honey bees can lead to colony losses, and thus purchases queens from excellent sources or rearing queens locally can improve colony productivity and health. For more information, please see the Honey Bee Best Management Practices guide that has been developed by the Managed Pollinator Coordinated Agriculture Program (CAP) and Project Apis m (PAm):

Reviews on Honey Bee Health

The Plight of Bees- Environmental Science and Technology
Dennis vanEngelsdorp, Marina Doris Meixner A historical review of managed honey bee populations in Europe and the United States and the factors that may affect them. Journal of Invertebrate Pathology 103 (2010) S80–S95

Solving the Mystery of the Vanishing Bees- Scientific American: April 40-47.

Nosema ceranae The Inside Story

Nosema Microsporidia: Friend Foe and Intriguing Creatures
Higes M, Martín-Hernández R, Botías,C, Garrido-Bailón E, González-Porto AV, Barrios L, del Nozal MJ, Bernal JL, Jiménez, JJ, García-Palencia, P, Meana, A. 2008

Honey Bee Disorders: Bacterial Diseases

Honey Bee Nutrition

UNEP EMERGING ISSUE- Honey Bee Colony Disorders and Other Threats to Insect Pollinators

Download this PDF to learn more about global Honey Bee colony disorders and other threats to insect pollinators.
Current evidence demonstrates that a sixth major extinction of biological diversity event is underway.1. The Earth is losing between one and ten percent of biodiversity per decade2, mostly due to habitat loss, pest invasion, pollution, over-harvesting and disease3. Certain natural ecosystem services are vital for human societies. Many fruit, nut, vegetable, legume, and seed crops depend on pollination. Pollination services are provided both by wild, free-living organisms (mainly bees, but also to name a few many butterflies, moths and flies), and by commercially managed bee species. Bees are the predominant and most economically important group of pollinators in most geographical regions. The Food and Agriculture Organisation of the United Nations (FAO)4 estimates that out of some 100 crop species which provide 90% of food worldwide, 71 of these are bee-pollinated. In Europe alone, 84% of the 264 crop species are animalpollinated and 4 000 vegetable varieties exist thanks to pollination by bees5. The production value of one tonne of pollinator-dependent crop is approximately five times higher than one of those crop categories that do not depend on insects. Has a “pollinator crisis” really been occurring during recent decades, or are these concerns just another sign of global biodiversity decline? Several studies have highlighted different factors leading to the pollinators’ decline that have been observed around the world. This bulletin considers the latest scientific findings and analyses possible answers to this question. As the bee group is the most important pollinator worldwide, this bulletin focuses on the instability of wild and managed bee populations."
Excerpts from the PDF


A Message from the Executive Director on CCD and Neonicotinoids

Neonicotinoids come with a bee hazard statement on the label as they have been determined to have the potential to harm bees; but the question is, to what extent are these substances alone responsible for CCD?  CCD has been shown to be the result of multiple factors, as detailed by the recent EPA-USDA report issued last week.  CCD, however, is just one of the many problems that have beset honey bees; and there are considerably more issues that face the rest of the pollinating community including other bees, bats, birds, butterflies, flies and more.

The Pollinator Partnership feels that science needs to lead the discussion on neonicotinoids, CCD, and all pollinator health issues, and that decisions based on anything less have the potential to lead us into more, not fewer, problems. 

Neonicotinoids were developed as a response to and as a replacement for previous chemicals that had proven risks associated with bee kills and human health concerns.  With respect to neonicotinoids, we really do not know enough yet; and we are hoping that new science, including research we are conducting this year, will help clarify this.   Having said this, we also know that no science will ever provide perfect, clear, unequivocal answers – sometimes it provides quite the opposite.  Also, the intuitive and sensitive observations of those in the field, namely beekeepers and citizen scientists, can provide invaluable insights into problems and solutions, but can also be subject to the blind spots and incomplete reporting of the untrained observer.  Add to this the distances where bee foraging can take place and the number of diseases and parasites that can be present, and a degree of uncertainty in cause and effect is inevitable.

When the question is complex, as this one is, the temptation to yield to a single, simple solution is a natural inclination but not always a productive one.  Are we even asking the right questions in our scientific inquiries?  Are we observing the total picture of the field experience?  Rather than studying or eliminating individual chemicals, should we be assessing the environmental milieu, the volume of chemical exposure and the interactions of pesticides?   With the use of neonicotinoids, must every seed be treated at every planting? What nutritional support may be lacking, due to monoculture, lack of forage, or insufficient circumstantial supplementation, even in the absence of chronic or acute exposures to pesticides?

Systemic pesticides deliver their benefits in a compact manner, reducing direct or drift exposure to non-target species, but they do so at a cost – they are applied in a prophylactic manner before the pest incident threshold is met and before other approaches can be attempted.  This is done as a protection to the crop and the producer, but potentially at the expense of pollinators.  In an altered scenario, who will bear the cost of the loss of the pollinators or the cost of the failed crop?  Do we really want to pit these two vital agricultural forces against one another?  Is there some way to work together to find a solution?

Today, over 40 different chemicals have been identified in samples of pollen collected by bees; which is the right chemical to eliminate?  Recent studies have shown that nutritional deficiencies have a significant role in suppressing bee defense systems when confronting any toxin. Varroa destructor, the mite that has plagued honey bees for 20 years has become a more persistent and ubiquitous problem; further, the accumulation of miticides applied as a potential remedy may have inadvertently exacerbated the situation. 

Changing weather patterns affect pollinators’ access to forage and water and may affect their own emergence in the delicate balance of phenology.  The record warmth of the winter of 2011 brought the lowest overwintering deaths since the onset of CDD, to be followed by harsher conditions the next year and a dramatic record high in bee deaths.  And finally, beekeepers who have never had any previous problems, even during CCD’s past 5 years, have seen catastrophic losses this year – since applications of pesticides have not changed, what would be the cause of this shift?  All of these questions point to factors that have been working together against the health of pollinators – what we don’t need is to compound the problem through less-than-rigorous solutions.

The Pollinator Partnership’s perspective is that real and lasting, positive change in the health of pollinators must be based on unfettered scientific analysis, the implementation of best practices on the part of producers, beekeepers, decision-makers and the public that take pollinators into account, and the engagement of all stakeholders in open and practical discussions that do not take statements, or science, out of context.  This is a position that, in a polarized society, is not easy to advocate or maintain; but we believe it is the only true path to progress in building sustainable ecosystems and agriculture, both of which depend on the extensive contributions of pollinators.  And both of which are urgently needed.

In working with all stakeholders, we choose to focus on the end result – our question is always - what will bring the greatest benefit to pollinators, support food production and a healthy environment, and in a practical and supportable way, build economic and food security and sustainability for the future? And that course of action requires thoughtful examination of evidence and thorough but expedient, strategic action.

We have listed most neonicotinoid studies on our website at LINK and would welcome any new studies for posting there.  We appreciate the concern for pollinators that we have helped nurture over these last 16 years; and we recognize how frustrating it is to all concerned not to be able to identify a smoking gun, a conspiracy or an easy path out of this mess.  We pledge that we will continue to seek engagement, sound science, consensus, and practical and expeditious actions to help pollinators.  We encourage those who support this approach to join us.  Feel free to send comments to  Thank you.

Best regards,

Laurie Davies Adams
Executive Directo

Colony Collapse Disorder (CCD) Update

Many newspapers and online journals have reported that a major step forward has been made in the research to unravel to mysterious disappearance and death of honey bees called Colony Collapse Disorder (CCD).  The assertion that CCD has been solved, however, is premature. 

A recently released study has identified a link between the presence of both fungus and virus in the dead bees sent to the researchers to examine for the disorder. However, the researchers themselves are unclear about the exact form of the virus or whether this relationship between the presence of both fungal and viral elements is the cause or the effect of CCD.  The true significance of the findings has yet to be defined.

Unfortunately, the results of this study have been distorted through what are usually reliable media sources.  Media claims of a solution to CCD are, regrettably, exaggerated.  Far from proclaiming that CCD is solved, news reporting should have signaled a new and potentially important step forward in the search for answers. Further adding to the confusion, the overwintering death rates for honey bees have continued at the same unsustainable and disturbing rate this year, but the cause of these deaths seems to be shifting AWAY from traditional CCD symptoms.

In short, exaggerated claims help no one, especially not bees.  At a time when there are thousands of critical issues clambering for attention, declaring a premature fix for a highly complex situation is tantamount to condemning honey bees to less attention, research and real solutions to their plight. 

Keeping perspective on results, demanding exacting science that withstands challenges, insisting on comprehensive and accurate reporting, and basing a prudent course on replicable science is the only way to ensure the future for honey bees, pollinators and the humans who depend on them.

While important research continues to unlock new clues, the beekeeping and research communities agree that this moment continues to be critical for the health of honey bees and all pollinators, and the mystery of CCD remains both complex and elusive.

Laurie Davies Adams
Executive Director


Honey Bee and Wild Bee Interaction

Updated April 2, 2012 –

The following list of peer reviewed publications has been generated by members of the pollinator LISTSERV. Some of these studies report tests of native bee/honey bee interactions, others provide background and insight into potential interactions. If you have an additional study to add to this list please email We are also in the process of developing a new 2012 NAPPC Task Force that will take on this issue. If you are interested in chairing or participating in this task force please contact Vicki Wojcik,

Peer Reviewed Publications

  1. Aizen MA and Feinsinger P (1994) Habitat Fragmentation, Native Insect Pollinators, and Feral Honey Bees in Argentine 'Chaco Serrano'. Ecological Applications 4(2) 378-392
  2. Badan EI and Vergara CH (2011) Potential negative effects of exotic honey bees on the diversity of native pollinators and yield of highland coffee plantations. Agricultural and Forest Entomology 13:365–372
  3. Burkle LA and R. Alarcón (2011)The future of plant – pollinator diversity: understanding interaction networks across time, space, and global change. American Journal of Botany 98(3): 528–538.
  4. Cairns CE, Villanueva-Gutiérrez R, Koptur S, Bray DB (2005) Bee populations, forest disturbance, and africanization in Mexico. Biotropica 37 (4):686-692.
  5. Dohzono I and Yokoyama J (2010) Impacts of alien bees on native plant-pollinator relationships: A review with special emphasis on plant reproduction. Applied Entomology and Zoology 45:37-47.
  6. Eickwort GC and Ginsberg HS (1980) Foraging and mating behavior in Apoidea.  Ann. Rev. Entomol. 25:421-46
  7. Ginsberg HS (1981) Historical development of bee foraging patterns in central new york state Psyche 88:337-346
  8. Ginsburg HS (1983) Foraging ecology of bees in an old field. Ecology 64: 165-175.
  9. Goulson D (2003)  Effects of introduced bees on native ecosystems.  Annual Review of Ecology, Evolution, and Systematics 34: 1-26.
  10. Goulson D, J C Stout, A R Kells Journal of Insect Conservation (2002) Do exotic bumblebees and honeybees compete with native flower-visiting insects in Tasmania ? Journal of Insect Conservation 6(3): 179-189
  11. Knowles D (1983/4) Flying jewels. Geo 5:46-57
  12. Kremen C, Williams NM, Thorp RW (2002) Crop pollination from native bees at risk from agricultural intensification. PNAS 99 (26) 16812–16816.
  13. National Research Council of the National Academies (2006). Status of Pollinators in North America. National Academy Press, Washington, DC.
  14. Paton DC (1985) Food supply, population structure, and behaviour of New Holland honeyeaters Phylidonyris novaehollandiae in woodlands near Horsham, Victoria. Pages 222-230 in Keats, A, et al, eds. Birds of eucalypt forests and woodlands: ecology, conservation and management. Sydney (Australia): Royal Australian Ornithologists Union and Surrey Beatty and Sons.
  15. Paton DC (1993) Honeybees in the Australian environment. Bio Science 43: 95-103
  16. Pearson J FW. (1933) Studies on the ecological relations of bees in the Chicago region. Ecol. Monogr. 3:375-441.
  17. Potts, SG,  JC Biesmeijer, C Kremen, P Neumann, Oliver Schweiger and WE Kunin. (2010) Global pollinator declines: trends, impacts and drivers. Trends in Ecology and Evolution 25 (6) 345-355.
  18. Pyke GH and Balzer L (1985) The effects of the introduced honey bee (Apis mellifera) on Australian native bees. Occasional paper nr 7. Sydney (Australia): New South Wales National Prks Wildlife Service.
  19. Roubik DW and Villanueva-Gutiérrez, R (2009) Invasive Africanized honey bee impact on native solitary bees: a pollen resource and trap nest analysis. Biological Journal of the Linnean Society 98: 152-160.
  20. Roubik DW, Moreno E, Vergara C, Wittmann D (1986) Sporadic food competition with the African honey bee: projected impact on neotropical social bees. Journal of Tropical Ecology 2: 97-111.
  21. Roubik, DW and H Wolda (2001) Do competing honey bees matter? Dynamics and abundance of native bees before and after honey bee invasion. Popul Ecol 43:53–62
  22. Sáez A, Sabatino M, and Aizen MA (2012) Interactive Effects of Large- and Small-Scale Sources of Feral Honey-Bees for Sunflower in the Argentine Pampas PLoS One 7(1): e30968.
  23. Schaffer WM, Jensen DB, Hobbs DE, Gurevitch J, Todd JR and M. Schaffer V (1979) Competition, foraging energetics and the cost of sociality in three species of bees. Ecology 60: 976-987.
  24. Steffan-Dewenter I and Tscharntke T (2000) Resource Overlap and Possible Competition between Honey Bees and Wild Bees in Central Europe. Oecologia 122(2):288-296
  25. Stout JC and Morales Cl (2009) Ecological impacts of invasive alien species on bees.  Apidologie 40: 388-409.
  26. Sugden EA and Pyke, GH (1991) Effects of honey bees on colonies of Exoneura asimillima, an Australian native bee. Australian Journal of Ecology 16: 171-181.
  27. Thomson DM (2004) Competitive interactions between the invasive european honey bee and native bumble bees. Ecology 85(2):458–470
  28. Thomson DM (2006) Detecting the effects of introduced species: a case study of competition between Apis and Bombus. OIKOS 114: 407-418
  29. Villanueva-Gutiérrez R, Roubik, DW, Colli-Ucán W(2005) Extinction of Melipona beecheii and traditional beekeeping in the Yucatán peninsula. Bee World 86 (2): 35-41
  30. Wenner AM, Thorp RW and Barthell JF. Removal of european honey bees from the Santa cruz island ecosystem. Pages 327–335 in Damiani, C.C. and D.K. Garcelon (eds.). 2009. Proceedings of 327 the 7th California Islands Symposium. Institute for Wildlife Studies, Arcata, CA.
  31. William M. Schaffer WM, DW. Zeh, SL Buchmann, S Kleinhans, MV Schaffer and J Antrim (1983) Competition for Nectar between Introduced Honey Bees and Native North American Bees and Ants Ecology 64(3): 564-577


Reports and other resources

  1. Morkeski A and Averill AL (2010) Wild Bee Status and Evidence for Pathogen Spillover with Honey Bees CAP Updates: 12: ild-bee-status-and-evidence-for-pathogen-spillover-with-honey-bees
  2. Thorp RW, Wenner AM and Barthell JF (1999) Pollen and nectar resource overlap among bees on Santa Cruz Island, click here to view.
  3. Learn more from the Pesticide Environmental Stewardship - Promoting Proper Pesticide Use and Handling.
Photo Credit to Zachary Huang, Michigan State University.