Do Bees Carry Diseases?


While we would like to encourage Bees into our gardens and open public places, we also don’t want to inadvertently introduce disease to where there was none originally. There are a few points to consider so you can take precautions and avoid having these diseases transmitted further.

So, do bees carry diseases? Yes, they do. But, you should not be too worried about catching these diseases yourself or infecting your pets but there are some other considerations to understand regarding general pests that affect the Bees.

This article will outline help in solving all the problems and questions you might have about bees and diseases. Below are the different types of diseases that bees are known to carry and the symptoms you would see and what you can do about it.

Different Types of Bee Disease

Nosema Disease

Nosema Apis is a microsporidian that invades the intestinal tracts of adult bees and causes nosema disease, also known as nosemosis. Nosema infection is also associated with black queen cell virus. It is normally only a problem when the bees cannot leave the hive to eliminate waste. For example, during an extended cold spell in winter or when the hives are enclosed in a wintering barn. When the bees are unable to void (cleansing flights), they can develop dysentery. I bet you never thought bees could get dysentery!

Nosema disease is treated by increasing the ventilation through the hive. Some beekeepers treat hives with antibiotics such as fumagillin. However, antibiotic use, or rather its overuse and resistance, is a world wide concern so is best avoided where ever possible.

Nosemosis can also be prevented or minimized by removing much of the honey from the beehive and then feeding the bees on sugar water in the late fall. Sugar water made from refined sugar has a lower ash content than flower nectar, reducing the risk of dysentery. Refined sugar, however, contains fewer nutrients than natural honey, which causes some controversy among beekeepers. A balance of approaches is recommended.

In 1996, a similar type of organism to Apis was discovered on the Asian honey bee Apis cerana and subsequently named Nosema ceranae. This parasite apparently also infects the western honey bee.

Exposure to corn pollen containing genes for Bacillus thuringiensis (Bt) production may weaken the bees’ defence against Nosema. In relation to feeding a group of bees with Bt corn pollen and a control group with non-Bt corn pollen a study was performed.

“In the first year, the bee colonies happened to be infested with parasites (microsporidia). This infestation led to a reduction in the number of bees and subsequently to reduced broods in the Bt-fed colonies, as well as in the colonies fed on Bt toxin-free pollen. The trial was then discontinued at an early stage. This effect was significantly more marked in the Bt-fed colonies. The significant differences indicate an interaction of toxin and pathogen on the epithelial cells of the honeybee intestine. The underlying mechanism which causes this effect is unknown.”

This study should be interpreted with caution given that no repetition of the experiment nor any attempt to find confounding factors was made. In addition, BT toxin and transgenic BT pollen showed no acute toxicity to any of the life stages of the bees examined, even when the BT toxin was fed at concentrations 100 times that found in transgenic BT pollen from maize.

Chalkbrood Fungal Disease

Ascosphaera apis is a fungal disease that infests the gut of the larva. The fungus competes with the larva for food, ultimately causing it to starve. The fungus then goes on to consume the rest of the larva’s body, causing it to appear white and ‘chalky’.

Chalkbrood (Ascosphaerosis larvae apium) is most commonly visible during wet springs. Hives with chalkbrood can generally be recovered by increasing the ventilation through the hive.

Stonebrood Disease

Stonebrood (Aspergillosis larvae apium) is a fungal disease caused by Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger. It causes mummification of the brood of a honey bee colony. The fungi are common soil inhabitants and are also pathogenic to other insects, birds, and mammals.

The disease is difficult to identify in the early stages of infection. The spores of the different species have different colours and can also cause respiratory damage to humans and other animals. When bee larvae take in spores, they may hatch in the gut, growing rapidly to form a collar-like ring near the larval heads. After death, the larvae turn black and become difficult to crush, hence the name stonebrood. Eventually, the fungus erupts from the integument of the larvae and forms a false skin. In this stage, the larvae are covered with powdery fungal spores.

Worker bees clean out the infected brood and the hive may recover depending on factors such as the strength of the colony, the level of infection, and hygienic habits of the strain of bees (variation in the trait occurs among different subspecies/races).

Varroa Mites

Varro destructor and Varro Jacobson are parasitic mites that feed on the bodily fluids of the adult, pupil and larval bees. Varroa mites can be seen with the naked eye as a small red or brown spot on the bee’s thorax. Varroa mites are carriers for many viruses that are damaging to bees. For example, bees infected during their development will often have visibly deformed wings.

Varroa mites have led to the virtual elimination of feral bee colonies in many areas, and are a major problem for kept bees in apiaries. Some feral populations are now recovering and it appears they have been naturally selected for Varroa resistance.

To the untrained eye, these mites are generally not a very noticeable problem for a strongly growing hive. The bees may appear strong in number and may even be very effective at foraging. However, the mite reproduction cycle occurs inside the capped pupae, and the mite population can surge as a result of colony growth.

Careful observation of a colony can help identify signs of the disease often spread by mites. When the hive population growth is reduced in preparation for winter or due to a poor late summer forage, the mite population growth can overtake that of the bees and this can then destroy the hive. It has been observed that diseased colonies may slowly die off and be unable to survive through winter even when adequate food stores are present.

Often, a colony will simply leave and not as a swarm, either. They will leave no population behind under such dire conditions.

Varroa Mite Treatment

A variety of treatments are currently marketed or practised to attempt to control these mites. The treatments are generally segregated into chemical and mechanical controls.

Common chemical controls include “hard” chemicals such as Amitraz, fluvalinate, coumaphos. “Soft” chemical controls include thymol, sucrose octanoate esters, oxalic acid and formic acid. According to the U.S. Environmental Protection Agency, when used in beehives as directed, these treatments kill a large proportion of the mites while not substantially disrupting bee behaviour or life span. Use of chemical controls is generally regulated and varies from country to country. With few exceptions, they are not intended for use during production of marketable honey.

Common mechanical controls generally rely on disruption of some aspect of the mites’ lifecycle. These controls are generally intended not to eliminate all mites, but merely to maintain the infestation at a level which the colony can tolerate. Examples of mechanical controls include drone brood sacrifice (varroa mites are preferentially attracted to the drone brood), powdered sugar dusting (which encourages cleaning behaviour and dislodges some mites), screened bottom boards (so any dislodged mites fall through the bottom and away from the colony), brood interruption and, perhaps, downsizing of the brood cell size. A device called the varroa mite control entrance (VMCE) is under development as of 2008. The VMCE works in conjunction with a screened bottom board, by dislodging varroa mites from bees as they enter and exit a hive

Small Hive Beetle

Comb slimed by hive beetle larvae: Hives infested at this level will drive out bee colonies.

Aethina tumida is a small, dark-coloured beetle that lives in beehives. Originally from Africa, the first discovery of small hive beetles in the US was made in the mid-1990s. The next year, a specimen that had been collected from Charleston, South Carolina, in 1996 was identified and is believed to be the index case for the United States. By December 1999, small hive beetles were reported in Iowa, Maine, Massachusetts, Minnesota, New Jersey, Ohio, Pennsylvania, Texas, and Wisconsin, and it was found in California by 2006. It really didn’t take long for this beetle to cover a large distance.

The lifecycle of this beetle includes pupation in the ground outside of the hive. Controls to prevent ants from climbing into the hive are believed to also be effective against the hive beetle. Several beekeepers are experimenting with the use of diatomaceous earth around the hive as a way to disrupt the beetle’s lifecycle. The diatoms abrade the insects’ surfaces, causing them to dehydrate and die. This is essentially a ground-fossil that has very sharp grains that cut through the soft bodies on new beetles. It is used by chicken keepers to control red mite.

Small Hive Beetle Treatment

Several pesticides are currently used against the small hive beetle. The chemical fipronil (marketed as Combat Roach Gel) is commonly applied inside the corrugations of a piece of cardboard. Standard corrugations are large enough that a small hive beetle can enter the cardboard through the end but small enough that honey bees cannot enter (thus are kept away from the pesticide). Alternative controls such as oil-based top-bar traps are also available, but they have had very little commercial success.

Wax Moths

Wax moth (Aphomia sociella) are more often associated with bumblebees.

Galleria mellonella (greater wax moths) do not attack the bees directly but feed on the shed exoskeletons of bee larvae and pollen that is found in dark brood combs, which was once used by the bees to hold the developing bees. Their full development to adults requires access to used brood comb or brood cells. These contain protein essential for the larval development, in the form of brood cocoons. The destruction of the comb will spill or contaminate stored honey and may kill bee larvae.

When honey supers are stored for the winter in a mild climate, or in heated storage, the wax moth larvae can destroy portions of the comb, though they will not fully develop. The damaged comb may be scraped out and replaced by the bees. Wax moth larvae and eggs are killed by freezing, so storage in unheated sheds or barns in higher latitudes is the only control necessary.

Because wax moths cannot survive a cold winter, they are usually not a problem for beekeepers in the northern U.S. or Canada, unless they survive winter in heated storage, or are brought from the south by purchase or migration of beekeepers. They thrive and spread most rapidly with temperatures above 30 °C (90 °F), so some areas with only occasional days that are hot rarely have a problem with wax moths, unless the colony is already weak due to stress from other factors.

Wax Moth Treatment

A strong hive generally needs no treatment to control wax moths; the bees themselves kill and clean out the moth larvae and webs. Wax moth larvae may fully develop in cell cleanings when such cleanings accumulate thickly where they are not accessible to the bees.

Wax moth development in the comb is generally not a problem with top bar hives, as unused combs are usually left in the hive during the winter. Since this type of hive is not used in severe wintering conditions, the bees are able to patrol and inspect the unused comb.

Wax moths can be controlled in stored comb by application of the aizawai variety of Bacillus thuringiensis spores through spraying. It is a very effective biological control and has an excellent safety record.

Wax moths can be controlled chemically with paradichlorobenzene (moth crystals or urinal disks). If chemical methods are used, the combs must be well-aired for several days before use. The use of naphthalene (mothballs) is discouraged because it accumulates in the wax, which can kill bees or contaminate honey stores. Control of wax moths by other means includes the freezing of the comb for at least 24 hours.

Asian Bee Mite (Tropilaelaps)

American foulbrood (AFB, Histolysis infectiosa perniciosa larvae apium, Pestis americana larvae apium), caused by the spore-forming Paenibacillus larvae (formerly classified as Bacillus larvae and Paenibacillus larvae ssp larvae/pulvifaciens), is the most widespread and destructive of the bee brood diseases. P. larvae is a rod-shaped bacterium.

Larvae up to three days old become infected by ingesting spores present in their food. Young larvae less than 24 hours old are most susceptible to infection. Spores germinate in the gut of the larva and the vegetative bacteria begin to grow, taking nourishment from the larva. Spores will not germinate in larvae over three days old. Infected larvae normally die after their cell is sealed. The vegetative form of the bacterium will die, but not before it produces many millions of spores. American foulbrood spores are extremely resistant to desiccation and can remain viable for 80 years in honey and beekeeping equipment. Each dead larva may contain as many as 100 million spores.

This disease only affects the bee larvae but is highly infectious and deadly to bee brood. Infected larvae darken and die.

European foulbrood

Melissococcus plutonius is a bacterium that infects the midgut of bee larvae. European foulbrood (EFB, Putrificatio polybacterica larvae apium, Pestis europea larvae apium) is considered less serious than American foulbrood. M. plutonius is not a spore-forming bacterium, but bacterial cells can survive for several months on wax foundation. Symptoms include dead and dying larvae which can appear curled upwards, brown or yellow, melted or deflated with tracheal tubes more apparent, or dried out and rubbery.

European foulbrood is often considered a “stress” disease — dangerous only if the colony is already under stress for other reasons. An otherwise healthy colony can usually survive European foulbrood. Chemical treatment with oxytetracycline hydrochloride may control an outbreak of the disease, but honey from treated colonies could have chemical residues from the treatment.

The “Shook Swarm” technique of bee husbandry can also effectively control the disease, with the advantage of avoiding the use of chemicals. Prophylactic treatments are not recommended as they lead to resistant bacteria.

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