Disease and pest control

Diseases

American foulbrood, caused by a spore-forming bacterium, Bacillus larvae, is the most serious brood disease. It occurs throughout the world wherever bees are kept and affects workers, drones, and queens. The spores are highly resistant to heat and chemicals. A comb containing brood severely infected with this disease has a mottled appearance caused by the mixture of healthy capped brood interspersed with diseased or empty cells formerly occupied by diseased brood. The decayed mass has a typical ropiness when dug into, which is one of its identifying characteristics.

American foulbrood can be spread to healthy colonies by transferring equipment or allowing the bees to feed on honey from infected colonies. Sulfathiazole and Terramycin are widely used to control the disease. Many countries and most states in the U.S. require the destruction by fire of diseased colonies and have apiary inspectors to enforce the regulations.

European foulbrood is caused by a nonsporeforming bacterium, Streptococcus pluton, but Bacillus alvie and Acromobacter eurydice are often associated with Streptococcus pluton. This disease is similar in appearance to American foulbrood. In some instances it severely affects the colonies, but they recover so that colony destruction is not necessary. Terramycin can control the disease.

Sacbrood is caused by a virus and is superficially similar to the foulbrood diseases. It can appear and disappear spontaneously but is seldom serious. No chemical control is needed. If the problem persists, the beekeeper usually requeens the colony.

Chalk brood is caused by the fungus Ascosphaera apis. The larvae victims of this disease have a chalky white appearance. Stonebrood, which affects both brood and adults, is also caused by a fungus, Aspergillus flavus, which can usually be isolated from bees that have stonebrood.

Nosema disease, caused by the microsporidian Nosema apis, is the most serious disease of adult bees. It is widespread, causes heavy losses in honey production, and severely weakens colonies. The external symptoms of bees with nosema disease are not apparent. The disease is transmitted from adult to adult by ingestion of the spores that soon germinate in the ventriculus, or main, stomach. An infected ventriculus is normally swollen, soft, and grayish white. A degree of control may be obtained by feeding the colony the drug fumagillin.

Acarine disease is caused by the mite Acarapis woodi that gets into the tracheae of the bee through its breathing holes or spiracles in its thorax or midsection. Bees affected by this mite are unable to fly, have disjointed wings and distended abdomens. There is presently no good control for this mite. The only U.S. federal law pertaining to bees was passed to prevent the importation of adult bees carrying this mite into the United States. Two other mites, Varroa destructor and Tropilaelaps clareae, which are native to Asia, are serious problems for beekeepers. V. destructor is now commonly found in Europe and North America, where it is capable of devastating entire colonies of honeybees.

There are other minor diseases of adult bees, but they seldom cause serious problems.

Pests

The greater wax moth, Galleria mellonella, is a lepidopterous insect that, in its larval stage, destroys combs. It does not attack adult bees but may begin destruction of combs of a weak colony long before the bees are gone. It can also destroy stored combs of honey. When the larvae are ready to pupate, they often eat out a place to spin their cocoons in the soft wood of the beehive, damaging frames and other hive parts. The best control for this pest is keeping colonies strong. Stored combs are fumigated, kept in a cold room, or stacked in such a way that a strong air draft flows around them.

The larvae of the lesser wax moth, Achroia grisella, cause damage to stored combs similar to that of the greater wax moth. The Mediterranean flour moth larva, Anagasta kuehniella, feeds on pollen in the combs and causes some damage. Control for both of these moths is the same as for the greater wax moth.

The bee louse, Braula caeca, is a tiny, wingless member of the fly family that is occasionally found on bees. It feeds on nectar or honey from the mouthparts of its host. Its larvae burrow in the cappings of honey combs.

Ants sometimes invade hives and disrupt or kill the bees. Termites can damage or destroy hive parts placed on the soil. Other insects, such as dragonflies (Odonata), robberflies (Diptera), praying mantises (Orthoptera), ambush bugs (Hemiptera), and certain wasps and yellow jackets (Hymenoptera) are natural enemies of the honeybee.

Predators

Mice frequently enter the hive in winter when the bees are clustered, or they get into stored combs and despoil or damage them by chewing the frames and combs to construct their nest. Skunks devour large numbers of bees at the hive entrance, usually at night. Fences, traps, and poison are used against them. Bears eat the honeybees and the brood in the hive, usually destroying it and its contents in the process. In bear country, electric fences and traps are used to protect bee colonies.

At times bees become their own deadly enemy. If honey is exposed to them when no flowers are in bloom and the weather is mild, the bees from different colonies will fight over it. Sometimes this fighting, or robbing, becomes intense and spreads from hive to hive in moblike action. If all the bees in one colony are killed, the honey is quickly stolen and carried into other hives. This further intensifies the robbing so that a cluster that was carrying honey into its hive a few minutes earlier is attacked, all of its occupants killed, the honey again stolen, and the process repeated. Usually, once robbing becomes intense, only darkness or foul weather will stop it.

Colony collapse disorder

One of the most mysterious disorders to strike honeybee colonies in the modern era is colony collapse disorder (CCD). It is characterized by sudden colony death, with a lack of healthy adult bees inside the hive. While the underlying cause is not known, it appears that the disorder affects the adult bees’ ability to navigate. They leave the hive to find pollen and never return. Honey and pollen are usually present in the hive, and there is often evidence of recent brood rearing. In some cases the queen and a small number of survivor bees may remain in the brood nest. CCD is also characterized by delayed robbing of the honey in the dead colonies by other, healthy bee colonies in the immediate area, as well as slower than normal invasion by common pests, such as wax moths and small hive beetles. The disorder appears to affect only the European honeybee (Apis mellifera).

CCD was first reported in autumn 2006 by a commercial beekeeper in Pennsylvania, who had colony losses estimated at 80 to 90 percent. Colony losses continued to be reported by other beekeepers in 35 states throughout the United States during the spring and summer of 2007, with many beekeepers losing anywhere from 30 to 90 percent of their hives. Beekeepers in other countries, including Canada, Portugal, Italy, Spain, Greece, Germany, Poland, France, and Switzerland, also reported substantial losses of honeybees. In the following years, the syndrome continued to impact honeybee colonies, though the percentage of colonies lost annually appeared to decline. Nonetheless, the potential economic impact on agriculture is great; annually in the United States alone an estimated $15 billion of crops are pollinated by honeybees.

Studies of adult honeybee carcasses from affected colonies indicate that the bees are infected with a number of pathogens and parasites, including viruses, species of Nosema, and the phorid fly Apocephalus borealis. However, scientists have not reached a definitive conclusion on whether a single pathogen is the root cause of the disorder, and many scientists suspect that a combination of factors are involved, such as a weakened immune system, brought on by colony stress, and the presence of pathogens, which are a constant threat and can be numerous in honeybee colonies. In addition, pesticides such as neonicotinoids (insecticides based on derivatives of nicotine) can be toxic to honeybees and are suspected of causing or contributing to CCD.