Health Problems
Major factors threatening honey bee health can be divided into the general areas of parasites and pests, pathogens, poor nutrition, and sublethal exposure to pesticides. In reality though, these factors tend to overlap and interact with one another, which complicates issues. In addition, there are other issues that have impacts on honey bee health such as the narrow genetic base of honey bees in the United States.
Parasites and Pests
Varroa mites (Varroa destructor) are essentially a modern honey bee plague. The Varroa mite has been responsible for the deaths of massive numbers of honey bee colonies since its arrival in the United States in 1987. A native of Asia, Varroa normally parasitizes the Asian honey bee, Apis cerana, which is a different species from the European or western honey bee, Apis mellifera, on which this country primarily depends for crop pollination.
Varroa mites directly damage honey bees by attaching and sucking the bees' equivalent of blood (hemolymph fluid) somewhat like ticks. They also indirectly damage honey bees because, similarly to mosquitos, Varroa mites also transmit an array of pathogenic viruses to honey bees such as deformed wing virus.
Beekeepers have identified Varroa mites as their single most serious problem causing colony losses today.
Small hive beetles, native to sub-Saharan Africa, were first found in the United States in 1996 and had spread to 30 States by 2014. Large beetle populations are able to lay enormous numbers of eggs. These eggs develop quickly and result in rapid destruction of unprotected combs in a short time. If large populations of beetles are allowed to build up, even strong colonies can be overwhelmed in a short time.
Wax moths arrived in the United States in 1998 in Florida. This can be a very destructive insect pest, damaging beeswax comb, comb honey, and bee-collected pollen. Wax moths are rarely the initial cause of colony failure but can overcome weak colonies.
Pathogens
Since the 1980s, many new exotic pathogens that infect honey bees have been found in this country. These include deformed wing virus, paralytic viruses such as Israeli acute paralysis virus, which was first found in 2004, European foulbrood bacteria, and Nosema ceranae fungi, which arrived in 2005. They have all become major problems for U.S. honey bees and beekeepers.
Poor Nutrition
Honey bees' natural diet comes primarily from nectar and pollen gathered from a wide variety of flowers. Insufficient or incomplete nutrition has come to be recognized as an essential factor that weakens the honey bee's immune systems and is likely to make bees more susceptible to all of the other problems troubling them today.
As demand for pollination services grows, bee colonies often are kept for more time on sites in a mono-crop environment before being moved directly to the next mono-crop area. As more and more land is lost to urbanization and suburbanization, it also means a loss of habitat with a diverse mix of nutritious bee forage plants. In addition, when it comes to helping bee colonies survive the winter and droughts, both times when nectar supplies can be scarce for bees, beekeepers often provide an artificial diet. Scientists are still trying to perfectly duplicate a bee's natural pollen/nectar diet for those times of the year when good forage is not available.
Pesticides and Sublethal Pesticide Effects
A survey of honey bee colonies conducted in 2010 by ARS researchers looked at 170 pesticides or their residues in honey bees, beeswax, and pollen. The data showed no consistent pattern of pesticide that differed between healthy and Colony Collapse Disorder affected colonies. The most commonly found pesticide in the study was coumaphos, which is used by beekeepers to treat honey bees for Varroa mites.
The pesticide class neonicotinoids (for example, clothianidin, thiamethoxam, and imidacloprid) has been accused of damaging or killing honey bees or being the cause of CCD even when the exposure is below the level expected to be toxic. The nicotine-based neonicotinoids were developed in the mid-1990s in large part because they showed reduced toxicity to wildlife compared with previously used organophosphate and carbamate insecticides.
The scientific data about the impact of pesticides and neonicotinoids in particular at environmentally and agriculturally realistic levels is mixed. Some findings have shown that neonicotinoids have sublethal effects on honey bees at or below approved doses and exposures. Documenting such sublethal effects is very difficult due to the many factors that can influence individual situations in field studies and during grower use including timing of use, health and nutritional state of the bees, total mix of pesticides, pathogens and parasites present, crop type, weather during the growing season, and accumulation of pesticides from year to year. Other studies have indicated that healthy colonies appear not to be impacted.
The U.S. Environmental Protection Agency (EPA) has strict regulations to protect managed honey bee colonies form incidents of pesticide misuse in formulation or application. Tips and complaints alleging pesticide-related bee incidents may be reported to State or tribal authorities or directly to the EPA Office of Pesticide Programs, beekill@epa.gov, National Pesticide Information Center or Guidance for Inspecting Alleged Cases of Pesticide-Related Bee Incidents.
Colony Collapse Disorder
In October 2006, some beekeepers began reporting losses of 30-90 percent of their hives. While colony losses are not unexpected, especially over the winter, this magnitude of losses was unusually high. Colony Collapse Disorder is specifically define by very low, or no adult honey bees present in a hive but with a live queen and no dead honey bee bodies present. Often there is still honey in the hive, and immature bees (brood) are present. Varroa mites, a virus-transmitting parasite of honey bees, have frequently been found in hives hit by CCD. No scientific cause for CCD has been proven. Most research has pointed to a complex of factors being involved in the cause of CCD, and possibly not all of the same factors or the same factors in the same order are involved in all CCD incidents.
In fact, the number of managed colonies that beekeepers have reported losing specifically from CCD began to wane in 2010 and has continued to drop. But the beekeeping industry continues to report losing a high percentage of their colonies each year to other causes.
Additional Threats
Northern Giant Hornet
Northern giant hornets, Vespa mandarinia, formerly known as the Asian giant hornet, are the largest wasps in the world. At roughly 2 inches in length, this invasive species from Southeast Asia has distinctive markings: a large orange or yellow head and black-and-orange stripes across its body.
Though its native range extends from northern India to East Asia, the hornet has been found in western Washington State as well as Vancouver Island and Langley, Canada and is classified as an invasive species in the United States.
The northern giant hornet is a threat to honey bees in its native territory and could also endanger honey bees in the United States if it becomes established here. NGH is also a health concern for people with bee or wasp allergies.
