What's Killing the Bees? New Study Offers Clues

 What's happening with the king of garden pollinators, the honeybee? Unfortunately, they are still disappearing and dying off. Numerous causes have been proposed and investigated for the honeybee problem known as Colony Collapse Disorder (CCD). But a 2010 USDA report about research into the disorder says the cause of the malady remains unknown. Researchers have learned that many different factors may work individually or in combination to cause the bee losses. Here's a summary of that 43-page report.

Definition of Colony Collapse Disorder (CCD):
(1) the apparent rapid loss of adult worker bees from affected colonies as evidenced by weak or dead colonies with excess brood populations relative to adult bee populations;
(2) the noticeable lack of dead worker bees both within and surrounding the hive;
(3) the delayed invasion of hive pests (e.g., small hive beetles and wax moths) and kleptoparasitism (stealing food) from neighboring honey bee colonies.

 

• Data on overall honey bee losses for 2010 indicate an estimated 34 percent loss, which is statistically similar to losses reported in 2007, 2008, and 2009.
 

• Currently, at least 5 North American bumble bee species are disappearing, with one species thought to have gone extinct within the last 5 years. Despite the rapid loss of these important pollinators, little is known about the cause of their demise.
 

• In a study of pesticide residues in bee colonies across 23 states, researchers found numerous pesticides and metabolites in the hive samples studied, increasing the opportunity for toxic interactions between the chemicals.
 

• Pennsylvania State University researchers found that consumption of sub-lethal levels of certain pesticides elevates viral titers (concentration of a substance) in infected bees and appears to alter the immune responses of the bees.
 

• Certain pesticides are suspected as a contributing factor to CCD. It is believed that bees have a relatively weak immune system as a result, and that this may be an evolutionary consequence of feeding on nectar and pollen. It has been noted in the literature that nectar and pollen in certain plant species harbor secondary plant compounds that are toxic to bees. And recently, scientists 
reported the occurrence of pesticides in pollen.
 

• Studies have also confirmed suspected links between CCD and poor colony health, inadequate diet, and long-distance transportation.
 

• Studies also showed that bees exposed to neonicitinoid insecticides and fungicides at sub-lethal levels had impaired bee immune systems and increased levels of viruses.
 

• This work suggests that a combination of environmental stressors may set off a cascade of events and contribute to a colony where weakened worker bees are more susceptible to pests and pathogens.

 

• Two recent studies have demonstrated increased levels of the gut parasite Nosema following exposure to sub-lethal levels of imidacloprid.
 

• When bees were exposed to the gut parasite Nosema and insecticide imidacloprid, researchers found evidence of an interactive effect on honey bee health. Worker bees exhibited up to a fourfold increase in Nosema levels when they originated from colonies that had been fed imidacloprid, indicating a subtle sub-lethal interaction between pesticides and pathogens

.

• In cage studies, nurse or house bees were fed sugar solutions containing pesticides (myclobutanil, acetamiprid, fluvalinate or chlorothalonil) at dosages previously determined to be sub-lethal. These dosages approximated lower concentrations found in incoming pollen. The titers (concentrations) of several picorna-like viruses (deformed wing virus, black queen cell virus, and IAPV) were found to be elevated by one or several of the pesticides.
 

• University of Massachusetts scientists assessed the impact of 
imidacloprid in flowering low bush blueberry on commercial bumble bees (Bombus impatiens). After bloom ended, the bees were released to forage on surrounding plants for the remainder of
the spring and summer. Results suggest that imidacloprid reduced brood (immature bees) at the end of bloom but did not seem to affect the survival of adult workers. 



• Soil and trunk injection of imidacloprid is used to treat hardwood trees in controlling the invasive Asian longhorned beetle. There 
is the potential for movement of the pesticide into pollen and nectar of treated trees.
 

• Noteworthy bioassay studies revealed synergistic effects of different chemicals on honey bee health. The studies revealed that these compounds (such as the pyrethroid pesticide fluvalinate, the organophosphate pesticide coumaphos and the fungicide prochloraz, if used in combination) produced an increase in toxicity to bees over what should be expected from use of the products individually.
 

• These studies show that the pesticides interfere with the bees’ detoxification processes, indicating that these pesticides can be safely used individually, but point to specific pesticide and fungicide combinations that may harm bees and should be avoided.
 

• A study by Pennsylvania State University scientists found that one fungicide (chlorothalonil) was linked with “entombing” behavior 
in bees (a defensive behavior associated with poor health) and had particularly detrimental effects.
 

• Findings currently suggest an association of sub-lethal effects of pesticides with CCD. Two common miticides in particular, coumaphos and fluvalinate, which are pesticides registered for use in bee colonies to control varroa mites, are suspect, either acting individually or in combination (e.g., synergistically, where the combination of the two compounds is more toxic than either compound alone).

 

• One study indicates potential interactive effects between varroa mites and small hive beetles on colony losses. Other studies also identified sub-lethal effects of neonicotinoids and fungicides on bees.
 

 

• Research results indicate that both supplemental protein diets and 
natural pollen feedings can increase colony strength and offset the negative impacts of stress caused by pests, pesticides, and long-distance transportation of bees by beekeeping operations.



• Studies have supported prior findings that supplemental 
protein feedings can strengthen honey bee colonies, while high-fructose corn syrup may cause colony stress.



• Other research has shown that ozone - a common means of controlling contamination and rotting of agricultural
 products - can also be used to kill bee pests and pathogens.



• Novaluron (Rimon) is a relatively new insecticide that is an insect growth regulator, labeled for lygus control in alfalfa fields during bloom. Some alfalfa leaf-cutting beekeepers have complained about poor bee returns in fields where novaluron was used, and laboratory trials have shown this pesticide to be toxic to larvae and eggs. 
 


• Pesticide Levels in Honey Examined. Overwintered honey is the source of carbohydrates for the bees during winter and pesticides
 present in the honey will be ingested by the bees. The miticides coumaphos and fluvalinate were observed more frequently and at higher concentrations than any other pesticide, and results 
indicate that coumaphos may have migrated from brood chamber use.



• Certain chemicals commonly found in plants may be toxic to bees, and University of Illinois researchers have found that genes in the honey bee genome may have a role in processing chemicals produced by the plant and encountered by honey bees when they feed on nectar. Recent studies revealed that several genes inside bees were activated when fed extracts of honey, pollen, and propolis. Findings indicate the possibility that genetic differences among honey bees could explain differences in their ability to detoxify compounds in nectars with high flavonoid content. This information could help beekeepers breed strains of honey bees that tolerate plants with toxic compounds in nectar and pollen.



• There was a significant reduction in adult bee longevity following
 exposure to 100 ppb of Coumaphos (an organophosphate insecticide used for control of a wide variety of livestock insects) in wax during the larval and pupal stages in worker honey bees. A 4-day reduction in summer bee lifespan was observed equaling 16 percent of the total
 lifespan of summer bees. Reduced adult longevity could impact honey production and or overwintering ability.
 

• First-year data from the Coordinated Agricultural Project (CAP) indicate that varroa mite infestation and viral diseases contribute strongly to colony losses.



• Research indicated that combinations of varroacides that are detoxified by the cytochrome P450 system (e.g., the
miticides tau-fluvalinate, coumaphos, and fenproximate) tend to be significantly more toxic when applied in combination. A similar interaction occurred when bees were exposed to a
cytochrome P450-inhibiting fungicide and a varroacide that was metabolized by P450s concurrently. Normally these varroacides are well tolerated by honey bees, but pre-treatment with a P450-inhibiting fungicide greatly increases mortality in bees by a synergistic ratio of nearly 2000X in the most extreme case.
 

• Honeybees should not be treated with more than one P450-detoxified varroacide concurrently or sequentially since varroacides are known to accumulate in beeswax.
 

• Beekeepers should avoid applying P450-detoxified varroacides when honey bees are placed in orchards or other crop settings where exposure to P450-inhibiting fungicides is likely.
 


• Controlled burns constitute one method used to manage fuel loads in natural areas, but the effects on pollinators remains unknown. Scientists completed a 2-year study in Zion National Park, home to 474 different kinds of bees, comparing bee pollinators in adjacent plots of burned and unburned forest and shrub land. In most cases, bee abundance was significantly greater in the burned areas 2 to 5 years after the burn. Burns thus represent opportunities for increasing pollinator populations during forest regeneration.



• Scientists are testing a new brood pheromone device in honey bee colonies to improve the health of honey bees, as well as to improve crop pollination. Field trials showing that treated colonies experienced increases in pollen collection and population.



• Cranberry pollination is extremely stressful to honey bees, providing minimal nutrition for the amount of work performed.  Scientists studied whether supplemental feeding with the MegaBee® protein supplement during cranberry pollination could reduce colony losses and improve colony population growth. Results showed that colonies fed the protein supplement grew more than those that were not fed, indicating that even a relatively small addition of supplemental protein to colonies during cranberry pollination improves their growth and survival.



• To evaluate the potential benefits of nutritional supplements on bee health, scientists compared protein levels, endocrine development, and immune response in adult worker bees that were fed protein, pollen, and high-fructose corn syrup supplements. Results showed that protein and pollen supplements produced similarly positive effects, but bees fed high-fructose corn syrup had
significantly reduced immune responses. 

 

• With the knowledge that pesticides could potentially have significant effects on bees, EPA recognizes the need for more
comprehensive testing of some pesticides and possible revision of past standards.
 

 

• Develop best management practices for non-Apis bees to provide alternative pollinators for crops, gardens, and natural areas.



• Guidance on managing blue orchard bees for almonds is now available to promote use of this bee and reduce pressure on 
honey bee colonies.
 

Bee Swarm in Chinese Pistache Tree

• Researchers are pursuing additional outreach opportunities 
using social networking sites and public Web pages. 

Honey bee health is featured on YouTube; 

on beekeeper Web forums such as beesource.com.; 

a new Extension website  has been assembled to provide reliable research-based information to beekeepers and the general public.

Bee Swarm Marching to a Hive