What is happening to the honeybees?  Why do beekeepers find once-thriving apiaries suddenly empty?  Why should anyone care?

The ‘what’ is fairly easy.  Scientists call it colony collapse disorder (CCD).  When a colony collapses from CCD, the bees from the hive simply disappear.  The sudden disappearance of honeybees should be of significant concern, as honeybees not only make delicious honey but pollinate many staple crops. (Cole)

The ‘why’ is much more challenging. Science has targeted pesticides, parasites, and pathogens as the three major suspects, yet not a single one of these has been universally accepted as the culprit.

Background

CCD is a recent and mysterious symptom afflicting apiaries (bee farms) worldwide.  Historically, other instances of suspected CCD have occurred during the 1880s, 1920s, and 1960s.  These historic incidents claimed inexplicable severe hive losses, just as today (USDA 2012).

Pesticides

One fact about pesticide use is indisputable: that demand for food production continues to increase and the use of pesticides has increased yields to meet those demands.  Even though pesticides are highly beneficial in this aspect, their contribution to CCD has been a highly controversial subject.

This section presents some of the arguments for and against pesticides as a causative factor of CCD.

Arguments made suggesting that pesticide use is inducing CCD:

·       Pesticide build-up could slowly kill off honeybee populations.

·       Pesticides may not kill off honeybees, but they may destroy behaviors essential for hive sustainability.

·       Effects of inert ingredients unknown.

Certain active ingredients of pesticides persist longer or tend to bioaccumulate, thereby prolonging exposure (Mullin).  Among these are lipophilic compounds, which accumulate in the honeybees themselves or in the wax they produce to expand and repair the hive.  This significantly increases the duration and concentration of exposure to the honeybees.  Because of this build-up, honeybees may not die after one application.   But several applications in quick succession, may be sufficient to cause severe losses.

        Sufficient doses of a pesticide could also weaken, disrupt, or kill beneficial species, including the honeybee.  Pesticide exposure in honeybee hives rarely reaches lethal levels yet it could still be considered a causative factor of CCD.  Most insecticides used can be technically classified as neurotoxins http://www.caes.uga.edu/applications/publications/files/pdf/B%201352_2.PDF (Suiter 8). Due to the dependence of honeybees on the hive culture, altering their nervous system may hamper the ability of foragers to navigate back to the hive or of workers to carry out duties necessary for the colony’s maintenance.  This would be severely detrimental to the sustainability of the hive and may be enough in certain situations to induce a colony’s collapse.

        Inert ingredients usually serve the purpose of stabilizing the active ingredients for better storage, safer handling, a longer duration of efficacy, and improving delivery and dispersion (Suiter 16).  The impact of these ingredients on the honeybee is not often subjected to rigorous study, and their contribution to CCD may be greater than previously thought.  However, this argument has little evidence since most studies focus on the active ingredients, and no firm hypotheses can be made as of yet.

Argument against pesticides as a direct factor in CCD:

·       Build-up can occur with certain pesticides, but if such were the case, then very strong correlations would be seen with these pesticides, and such trends have not been universally reported.

·       Pesticide bans have not reversed the occurrence of CCD.

·       Regulations and evaluations are already in place to protect beneficial species from significant pesticide exposure.

Several factors affect the potential of pesticides to build up to sufficient exposure levels to cause substantial negative impacts on honeybee populations.  A significant number of pesticide compounds currently in use have a relatively short half-life for their active ingredients.  Many compounds break down and lose their activity after mild exposure to UV rays, water, or even warm temperatures (Suiter 10).  This prevents build-up of these compounds from occurring in the bees or in their hives. Rapid decomposition is not common in all cases, but if pesticide build-up was a major issue, a very strong trend would be observed between those specific compounds and CCD.  No such trends have been discovered as of yet, and are not likely to have been overlooked.

        In European countries, there have been bans placed upon many different types of pesticides.  Although many people consider this a victory, there has not been recovery of the honeybees to pre-CCD numbers in any instance, suggesting that pesticides are not always a major factor in all CCD cases.

In the United States, the Environmental Protection Agency (EPA) approves pesticides for use while also establishing regulations for their application.  The EPA routinely reevaluates and re-registers each approved chemical, as large-scale extended use reveals new interactions previously unanticipated or unknown (U.S. EPA).  This process can be slow and time consuming, and unfortunately does not guarantee that all positive and harmful effects are accounted for in all situations.  Even so, the EPA states that no evidence has been given that any approved pesticide is a direct factor of CCD (http://www.epa.gov/pesticides/about/intheworks/honeybee.htm).  Large scale studies have also been performed by both the USDA and other privately funded organizations in attempt to discover correlations between certain pesticides and CCD, and have had similar results.

Parasites

The Varroa Destructor, an infamous parasitic mite, presents a special threat to honeybees. The Varroa mite's life cycle begins as an egg in a capped-off brood cell.  It hatches within a week and begins to feed on the hemolymph (blood) of the bee.

Female mites experience two life stages: a phoretic phase, in which she simply feeds, and a reproductive stage. To reproduce the female climbs into a healthy brood cell just prior to the cell's being capped off. A foundress, or reproducing female mite, mates only once but may lay eggs in different brood cells as long as she lives, which may be from two to six months.

The size of the mites doesn't reflect the amount of damage that they can cause to honeybees. Lots of tiny bloodsucking creatures make a big impact. The Mid-Atlantic Apicultural Research & Extension Consortium observed that “heavy parasitism results in heavy bee mortality and subsequent weakening of the colony and can lead to colony death.” (http://agdev.anr.udel.edu/maarec/wp-content/uploads/2010/03/Varroa_Mites_PMP2.pdf)

The ease with which mites spread between colonies makes them a global threat. Countries that do not already have the mite have taken actions to prevent its introduction. But for all their threat, some measures have been developed to help contain the mites. Eastern bees, such as bees from Russia and Asia, have apparent natural defenses against Varroa mites. Introduction of Eastern bees and brood into American hives has become a popular countermeasure to the threat of Varroa mites..

Apicultural researchers Ellis and Nalen noted the effects of hygienic behaviors in bees:

“Bees that are hygienic can detect many problems that affect brood (American foulbrood, varroa, chalkbrood, etc.), even if the brood is capped, and remove the affected brood. Because varroa mites go into cells immediately prior to the cell being capped, hygienic bees are given little time to 'find' varroa before the cell is capped. As a result, hygienic bees have a refined ability to detect varroa in capped cells, remove the capping, and abort the brood... It is interesting to note, a heightened form of hygienic behavior called 'varroa sensitive hygiene' (VSH) has been found in some bees. VSH bees are able to detect varroa in capped cells and remove... those varroa that are reproducing.” (http://entomology.ifas.ufl.edu/creatures/misc/bees/varroa_mite.htm)

Apparently, cleanliness does matter. For hives that don't or can't take care of themselves, beekeepers have another option: miticides, chemicals specifically engineered to kill parasitic mites. Miticides vary in strength and cost, and often availability depends on the region.

While the mites can cause colony death, the symptoms of death by mites do not strongly match the symptoms manifested in CCD. One of the main symptoms of CCD is a hive noticeably empty of bees, dead or alive. Apists whose hives are deluged with Varroa mites often find dead bees in their hives. Also, considering that Varroa mites are clearly visible on inspection, their presence would easily be detected as the culprit for CCD. Measures are available to counteract Varroa infestations that have shown effectiveness when employed. The use of such counteractive measures have not hindered or stopped the occurrence of CCD. It may therefore be hypothesized that colony collapse disorder cannot be wholly attributed to Varroa Destructor.

Pathogens

Although varroa mites do not constitute the main cause of CCD, they can bring another threat to the colony: pathogens. Colloquially known as germs, any microorganism that can cause a disease qualifies as a pathogen.

The Deformed Wing Virus has wiped out billions of honeybees throughout the globe (Gill 2012). It is one of the deadliest pathogens carried by Varroa Mites and the only way to control this virus is by controlling the mites.

Another one of the most common pathogens among bees, Nosema Ceranae, does not come from varroa mites. Instead, bees ingest Nosema spores when they drink at contaminated water sources.

Nosema wouldn’t be a cause of CCD because of two reasons; first, only forager bees ingest the contaminated water and they don’t live for much longer. Some of them will even fly away from the hive and not return to prevent contamination. Second, the only way for other bees to become infected would be through bee droppings and Infection of other bees wouldn’t happen because of something called cleansing flight, where bees fly out to defecate. A hive epidemic often happens during extended cold or rainy weather when bees don’t tend to go out for cleansing flights. To make matters worse the parasite causes the bees to have dysentery so that the infected bee will have to defecate more frequently. The huge problem here: now the hive will need a clean-up, and the hive reserves this lovely job for newly emerged bees. When these young bees get infected they lose their ability to digest pollen, and as a result they will not develop their hypopharyngeal glands. If the hive is taken over by the virus it will eventually become incapable of producing honey (Burlew 2013).

According to the Agricultural Research Service, no one pathogen directly correlates with the majority of CCD incidents. Instead, a combination of several viruses and bacteria can cause collapse.

Combination:

“The interactions between pesticides, mite stresses and diseases are likely contributing factors, and support an emerging hypothesis that no one factor alone can be held responsible for the dramatic losses of honey bees in general or for CCD specifically” (Mullin).  The following will briefly discuss a combination of the aforementioned factors and how they affect honey bee populations.

Mites, Varroa mites in particular, can have a large impact on the survival of bee colonies. Varroa mites are a parasite that feed on hemolymph (blood like material in arthropods), and can only reproduce in honey bee hives as far as we can tell.  

What makes Varroa Mites a threat?

• Males- short life cycle, primary function is reproduction
• Females- flat shape with a hook-claw to attach to abdominal area of host
• Camouflage- hard outer cuticle, protects and blends with the host during hive infiltration
• Once V. Mites transfer to a new host puncture wounds remain exposed on last victim
• Carrier for viruses between hives

Viruses and pathogens are also a known factor in honey bee colony collapse, and can be very devastating to various regions they are directly exposed to.

What makes Viruses a threat?

• Microsporidia only grow within a living host, making them difficult to study
• Vary in degree of harm from deformations, weakening organism, or even death
• Ability to rapidly become more tolerant to counter measures

Pesticides are also a contributing factor to the collapse of honey bee colonies around the world. As agriculture takes new strides in advanced chemicals to combat harmful organisms and increase profit margins, there will always be a negative consequence of those chemicals.

How do pesticides affect honey bee populations?

• Chemicals are taxied back to the hive as bees transport pollen with agrochemicals in it
• Hives become a drainage sink for nearby chemicals being used
• Chemicals affect the metabolism of pollen, a main staple of protein in bees diet
• Low protein metabolism affects the growth of bee offspring

Conclusion:

These contributing factors on an individual basis are not sufficient to cause a large scale collapse of Colony Collapse Disorder (CCD) around the globe. Pesticides are obviously a problem for hives, but pesticides and agrochemicals are a newer issue and CCD has been around for much longer. Varroa Mites have been around for a very long time, but have never been known to directly result in the collapse of a hive. And lastly bees have been largely impacted from pathogens and viruses, but in the past most bees were resistant and there wasn’t a large concern from them. As these factors have combined however, new battles have begun around the globe. V. Destructor Mites leave bees weaker and with open flesh wounds allowing chemicals and pathogens to more easily harm bees. Bees are being transported around regions, bought/sold, and any mite or virus infected hives are spreading to other colonies. Chemicals are also weakening the bees and directly causing problems for offspring. These three issues in tag team fashion are a force to be reckoned with.