8. Diseases, Pests and Pesticides affecting honey Bees
The honey bee is subject to many diseases and pests as are other insects and livestock. The diseases differ in their severity but all of them can be prevented or controlled by proper management. Such management includes knowing and recognizing the symptoms of diseases, inspecting colonies regularly, and applying control measures promptly when disease is found. Drugs and antibiotics are effective in preventing disease but cannot substitute for good management. They must be used at the proper time and dosage to avoid contamination of honey.
The diseases of bees are usually divided into two classes - those that attack the developing stages (the brood), and those that attack adult bees. In general, the brood diseases are more serious and their symptoms are more definite and distinctive than those of the adult diseases. It takes experience and close observation to distinguish a diseased larva or pupa from a healthy one, or one dead from other causes. This experience can be gained only by frequent examination of the combs of a colony. This is one of the reasons why the beginning beekeeper must open the colonies regularly.
American foulbrood. This disease, usually called AFB, has always been a problem in beekeeping. It is caused by a bacterium, or germ, called Bacillus larvae, which has a long-lived, resistant spore that can remain dormant for more than 50 years in combs and honey. When food containing spores is fed to a young larva, the spores germinate and multiply until they kill the developing bee just after its cell is sealed. Until that time no symptoms of the infection are visible except perhaps a slight graying or dullness of the usually glistening white immature insect. The infected bee dies as a larva stretched lengthwise in the cell, or as a new pupa with the body features of an adult bee. The capping of an infected cell may be slightly sunken and darker than healthy ones around it. Adult bees often puncture the cappings of infected cells and may remove them entirely. Since there are also holes in cells containing healthy larvae being capped, you must learn to distinguish them from abnormal ones. Worker, drone, and queen larvae and pupae are all susceptible to American foulbrood.
A dead larva infected with American Foulbrood shown head on. It shows the typical melted appearence, even color, and straight position in the cell. The cell walls and cappings were broken to expose the larve. (Fig. 70)
The larva or pupa that dies of AFB always lies perfectly straight on the lower side of the cell (Fig. 70). It loses its pearly white color and rapidly turns light brown similar to the color of coffee with cream. As it continues to decay and become dried, it turns dark brown and, finally, it turns into a black dried scale on the lower side of the cell. Other characteristic symptoms of American foulbrood are the somewhat glossy, uniform color of the dead larva or pupa, and the melted look as the body and the body wall rot. Sometimes the bacteria make the pupal tongue stick to the top of the cell. When this happens, the tongue looks like a smooth, fine thread extending vertically across the cell. However, many advanced cases of American foulbrood do not show this symptom.
The bacteria rot the skin of the developing bee and turn the body into a slimy mass that becomes stickier as it dries. This condition is the basis for the "ropiness" test that can be used to aid in diagnosing the disease. When making a diagnosis, you should carefully remove the capping from a cell that appears abnormal, but do not touch its contents untill you have closely examined their color, position, and other features. Only then should you touch the dead remains with a straw, toothpick, or match stick. Do not use a hive tool for this purpose. Watch to see what happens when you poke the remains. The larva or pupa with AFB will often collapse into a rubbery mass. Stir it with the stick and withdraw it slowly. If it strings or "ropes" out, see how far it will pull out. More important however, is what happens when the string breaks. If the cell is infected with American foulbrood, the mass on the stick should look like a drop with no sign of the drawn-out string. The remains left in the cell should be smooth with no sign of the drawn-out piece. In contrast, a cell infected with European foulbrood usually strings out and breaks off like a piece of dough or taffy.
The odor of American foulbrood is distinctive but is not a reliable indicator because people's sensitivities to odors vary so widely, and the odor may be strong or weak. The odor is similar to that of oldfashioned animal glues that are now rarely used. However, it is better to rely on your eyes to diagnose the disease.
The black scales resulting from infection with American foulbrood blend with the color of dark combs and are difficult to recognize. To see them, hold the comb so that sunlight strikes the lower side of the cells. The faint outline of the scale and the slightly raised head portion of it will then be evident. When examining combs of dead colonies, look for any sign of scales. They may be the only disease symptom present in the hive.
American foulbrood is spread by the exchange of infected honey and combs between colonies, either by the beekeeper or by robber bees. Infected colonies rarely recover and as they become weakened and die, they are often robbed by bees from nearby colonies. Reduce the size of the entrance of any weak colony, and close any dead colony and remove it from the apiary. You must be certain that weak or dead colonies do not have AFB before you exchange an), combs or honey from them or unite them with other colonies.
If you need help in inspecting your colonies or diagnosing disease, it is available in most states on request from the Department of Agriculture. The best time for inspection is the period from mid-March to about June 1st, before the nectar flow begins. Samples of diseased comb for laboratory examination can be sent to the Bioenvironmental Bee Laboratory, USDA-SEA , Building 476, BARC-East, Beltsville, Maryland 20705. Select a sample of brood comb about 5 inches square that contains large numbers of affected cells. Mail it in a strong cardboard or wooden box without an airtight wrapping. Samples that are crushed or moldy because of improper packaging make diagnosis impossible.
Disease control is primarily the responsibility of each beekeeper, who must learn the symptoms of the diseases and inspect the colonies carefully for the presence of American foulbrood. At the minimum, inspect your bees in the spring and the fall. It may also pay you to inspect colonies before putting on the honey supers and when you remove honey. At least one of the latter two inspections is essential if you have previously lost any colonies to American foulbrood. Bee diseases are spread more often within beekeeping operations than between them, and lack of inspection is a major cause of such spread.
Most state laws require the burning of colonies of bees infected with American foulbrood. The colony must be killed and all the contents of the hive burned, including bees, combs, frames, and honey. The fire should be built in a pit and the ashes covered afterwards. The cover, bottom board, and hive bodies should be scraped and then scorched. A blowtorch or weed burner is suitable for scorching small quantities of equipment. For large quantities, brush the inside surfaces with a mixture of onehalf gasoline and one-half motor oil and stack the hive bodies four or five high. Light the stacks and allow them to burn long enough to lightly char the wood. Place a cover over the stack to put out the fire. Afterward, separate the hive bodies and be sure that all the fire is out or it may later burn up the equipment.
Many methods of saving and treating diseased colonies have been tried and found to be ineffective. These methods sometimes require more expense and labor than the value of the diseased colonies. When not done properly, the treatments often spread disease. Inspection and prevention are the best methods of control. The only approved medicinal agent for preventive feeding for American foulbrood is oxytetratycline HCl (Terramycin). This material does not kill the disease organism but prevents its growth when present in low concentrations in the food fed by the workers to larvae.
Terramycin is relatively unstable in honey or syrup solutions and is best used as a dust in mixture with powdered sugar. It is available in at least two forms and in three concentrations of the active ingredient. Terramycin TM-50D contains 50 grams active material per pound, Terramycin Animal Formula Soluble Powder (TAFSP), usually called TM-25, contains 25 grams active material per pound, and Terra- mycin Feed Premix (TM-10) contains 10 grams active material per pound. All of these compounds must be diluted with powdered sugar for application to colonies of bees. A ready-to-feed mixture is also available. The desired dosage of 200 milligrams per ounce feeding can be achieved as follows:
Product formulation Amount of drug Amount of sugar
10 g/lb. 2-1/2 tsp. (1/3 oz.) 3 tbsp. ( 1 oz.)
25 g/lb. 1 tsp. (1/8 oz.) 3 tbsp. (1 oz.)
50 g/lb. 1/2 tsp- (1/16 oz.) 3 tbsp. (1 oz.)
For larger quantities, increase the amounts according to the number of colonies to be fed, or follow directions supplied by the manufacturer.
Place 3 level tablespoonfuls of the drug-sugar mixture over the top of the frames at the outer edge of the brood nest. Three dustings at 4- to 5-day intervals are recommended. The drug in this concentration is toxic to larvae and should be kept from contact with brood. Decrease the amount of the drug mixture given to weak colonies.
Any medicinal agents or mixtures should be applied only after inspection in the spring and at least 4 weeks before the main nectar flow. They may be used again after the honey is removed in late summer or during the fall. Use them with care at the proper dosages, and follow the directions and precautions on the labels. The products are available at beekeeping supply companies, livestock supply stores, and feed stores.
European foulbrood. This brood disease, usually called EFB, appears to be much less common than American foulbrood in the Midwest. It is caused by a bacterium, Streptococcus pluton, that does not always kill the infected larva but sometimes may kill large numbers of larvae very rapidly. The disease and its symptoms are highly variable, probably because of the presence of several other organisms in the dead and dying larvae. EFB does not usually kill the colony, but a heavy infection will seriously reduce honey production. It is not necessary for beekeepers to kill colonies infected with EFB, but it is essential to be able to distinguish European from American foulbrood disease.
Larvae infected with EFB usually die while still coiled in the bottom of the unsealed cell. This is distinctly different from what occurs with AFB. In some instances the disease may also affect sealed larvae and, rarely, pupae. When this happens, the larva usually dies in a partially curled or distorted position, only rarely lying straight on the lower side of the cell as it does when infected with American foulbrood. Affected larvae are not always the same color, as with AFB, but may be yellow, gray, or brown, or a mixture of these colors. The air tubes, or tracheae, often remain visible in the larva infected with EFB. Their presence helps to distinguish the disease from AFB, in which no tracheae can be seen in the decaying brood. The odor of European foulbrood may be described as being sour or similar to the odor of rotting fish. As with AFB, it is best not to use odor for diagnosis because of its variability and the differences in the ability of people to distinguish odors.
The typical consistency of EFB-infected larvae is doughlike. The remains may be somewhat ropy but less slimy and elastic than those of AFB-infected bees. When pulled out of the cell, the material reacts like dough or taffy when the pieces separate. Dried scales in comb may appear similar to those of American foulbrood if lying straight in the cells. However, most of them are turned or twisted in the cell and can be easily removed, whereas the scales of AFB are difficult to remove. Worker, drone, and queen larvae are all susceptible to EFB.
European foulbrood may be controlled by use of Terramycin in the same way as American foulbrood. This dual control exerted by the antibiotic makes it a good choice for preventive feeding where both diseases are a threat. Honey bee strains vary in their resistance to European foulbrood. When only one or a few colonies are affected, they should be requeened with a different strain of bees. The organisms associated with European foulbrood are usually present even in hives that do not show symptoms of disease. The susceptibility of the particular strain of bees and, perhaps, nutritional factors bring about the appearance of the disease at damaging levels.
Sacbrood. Sacbrood disease is caused by a virus and is common but rarely serious in the Midwest. Like European foulbrood, it must be distinguished from American foulbrood.
The presence of sacbrood-infected larvae produces a spotted appearance of the brood combs, a condition shared with all other brood diseases. The larvae die extended on the lower side of the sealed cells, and after they die part or all of the cappings may be removed by the adult bees. The skin of the dead larva does not rot as it does if the larva has died of foulbrood. Instead, it remains tough and encloses the watery contents like a sack, giving the disease its name. The head of the dead larva darkens more rapidly than the rest of the body and stays upright in the cell. It has been compared with the tip of a wooden Dutch shoe (Fig. 71). The elevated head of the completely dried larva remains readily visible in the cell. Such a scale is easily removed from the cell.
Two larvae, in uncapped cells, infected with scarbrood disease. (Fig 71)
Sacbrood is most common in the spring, usually affecting only a few cells in a comb. Occasionally very susceitible queen may have large numbers of affected larvae. The disease usually requires no treatment. severe cases, the colony should be requeened with a young queen from a different strain of bees.
Other brood diseases. Another brood disease has become established in many areas of the Midwest. It is called chalkbrood and is caused by a fungus organism called Ascosphaera apis. The fungus kills the larva after it is stretched out in the cell, turning it into a hard, white mummy. It may be covered with small black spots, which are the reproductive bodies of the fungus. Such mummies can be seen in the combs of infected colonies and on the landing boards of the hives where they are often dropped by house- cleaning bees. The disease may become severe in some colonies but is not expected to be a serious problem for beekeepers. There are probably differences in resistance among strains of bees, and requeening with a different strain may be of value in some cases. No control measures using drugs or chemicals are approved as yet.
Diseases too rare to discuss are parafoulbrood, a bacterial disease similar to European foulbrood, and stonebrood, caused by a fungus. Plant poisoning of brood is also rare in the Midwest.
Chilled or starved brood may sometimes be confused with diseased brood. Such brood is usually found outside the cluster area of small colonies and lacks most of the specific symptoms of the diseases because all brood stages may be affected. When the weather warms or the colony receives a new supply of food, the bees will quickly clean out all of the dead brood.
Adult Bee Diseases
Adult bees suffer from several diseases that are usually found in most colonies but rarely cause serious damage. In some parts of the world, a mite, Acarapis woodi, causes acarine disease when it infests the tracheae or breathing tubes of the bees' thorax. The Federal Honey Bee Act, enacted August 31, 1922, was amended in recent years to prevent the introduction and spread of diseases and parasites harmful to honey bees in the United States. This internal parasitic mite, however, was confirmed July 1984 in honey bee colonies in the state of Texas. It is believed that the mite crossed the border from Mexico. A national honey bee tracheal mite survey began, and within five months the mite had been identified in eight other states.
Several other species of external mites infest honey bees in the United States and elsewhere, but the extent of such damage has not been measured. Some mites found in honey bee colonies in other countries, particularly in the tropics, cause serious injury to developing brood.
Noserna disease. Nosema disease is an infection of the digestive organs of the adult bee by a single-celled organism, a protozoan called Nosema apis. Small numbers of infected bees may be found at almost any time of year in apiaries throughout the United States. The natural defenses of the individual and the colony against disease tend to keep it under control. However, when the bees are confined to the I-lives by poor spring weather, or subjected to stress from moving or special manipulations, such as those for queen rearing and for shaking package bees, the disease may reach damaging levels. The lives of infected bees are shortened, and affected colonies are weakened but rarely killed.
Nosema-infected colonies do not show any symptoms that are typical of the disease. For this reason, positive diagnosis can be made only by examination of bees for the presence of spores of Nosema apis. To do this, ground-up abdomens or alimentary tracts must be examined under a microscope at 40OX magnification to detect the organism.
The disease is cyclical in its severity in the colony, with the greatest infection in late spring and the least in late summer or fall. It can be controlled, at least in part, by feeding the antibiotic fumagillin (Fumidil B). Complete control is difficult because of the chronic nature of this infection in the bee's alimentary canal. The antibiotic must be available to the bees for a considerable time to rid them of the organism. The spores of the nosema organism are spread within and outside the colony with food and water. Infected bees soil the combs and spread infection within the colony. However, nosema infection does not cause dysentery, but bees suffering from dysentery may or may not have nosema disease. Empty combs contaminated with spores may be heated to 120 degrees F. (49 degrees C.) for 24 hours to kill the spores. Treatment is worthwhile; it reduces winter losses and creates stronger colonies in the spring. Treated colonies may also produce more honey. The antibiotic is most effective if fed in the fall when the normal level of the disease is lowest. Treatment in the spring is less effective but may be of value for nucleus or package colonies.
Dysentery. Although it is not a disease, dysentery is considered here because so many beekeepers think of it as a disease symptom, especially of nosema disease. Bees with dysentery are unable to hold their waste products in their bodies and they release them in the hive or close to it. The condition is recognized by the dark spots and streaks on combs, on the exterior of the hive, and on the snow near the hive in late winter (Fig. 72). Dysentery is caused by an excessive amount of water in a bee's body. The consumption during the winter of coarsely granulated honey or honey with a high water content is one cause of the disease. Damp hive conditions may also contribute to the problem. Good food and proper wintering conditions are important to prevent the problem but there is no specific control for it once the bees are affected. The colony's recovery may be helped if it is given combs of low-moisture honey or fed heavy sugar syrup. Combs from colonies with dysentery can be used safely in other colonies.
Dysentery of bees is indicated by the spotting of the hive and the snow around it in late winter. (Fig. 72)
Paralysis. Paralysis is the name given to several similar ailments of bees caused by viruses. Affected bees often shake and twitch and are unable to fly. In some cases the infected bees die within a day or two; in others, the life of the bee may only be shortened to about two-thirds its usual length. Normal bees may pull and bite the infected bees, causing their bodies to be partially hairless and shiny. The abdomens of such bees may also be enlarged. At present there are no special controls except to requeen the colony with a queen from a totally unrelated strain of bees. There appear to be distinct differences in susceptibility of different lines, races, and strains of honey bees to the viruses.
Other diseases of adult bees. Adult bees also suffer from other diseases such as septicemia and amoeba disease. Both are extremely rare and of little importance in the United States.
Pests of Honey Bees
Wax moths. The greater wax moth, Galleria mellonella, is a serious pest of honey comb in most areas of the United States. The adult moths are gray- brown and about 3/4 inch long. In the daytime they are usually seen resting with their wings folded like a tent over their bodies (Fig. 73). When disturbed, the moths usually run rapidly before taking flight. They lay their eggs on unprotected honey combs and in the cracks between hive bodies of colonies of bees. The grayish-white larvae (Fig. 74) are kept under control by the bees in normal colonies and do no harm. They may completely ruin the combs in weak or dead colonies and in stored equipment. Unless they are controlled, they feed on the cocoons, cast skins, and pollen in the combs, and reduce them to a mass of webs and waste products (Fig. 75). Keeping strong colonies and protecting stored equipment (see page 108) are the best ways to avoid damage from wax moth.
Adult greater wax moths in a typical resting position on comb foundation. (Fig. 73)
Several other less common moth larvae are sometimes found in combs. They usually feed only on the pollen in individual cells and are rarely pests. Furnigation and treatment for greater wax moth controls all such moths.
Larvae of the greater wax moth nearly full grown. (Fig. 74)
A stored comb ruined by feeding of wax moth larvae. Coocoons are visible among the webbing and on the frame top at the bottom of the illustration. (Fig. 75)
Mice. Mice are a pest of stored combs and unoccupied combs in bee hives, usually in the fall and winter. They chew the combs, eat pollen, and build nests among the combs. In the late fall, hive entrances should be reduced to 3/8 inch in depth either by entrance cleats or by reversing the bottom board to the shallow side. Excluders or tight covers on stacks of stored combs will help to keep them mouse-free. Since mice may chew into the supers, storage areas should be protected with bait boxes containing an effective mouse poison. In apiaries where mice are a serious problem, poison bait may be placed beneath the hives or in bait boxes within an empty hive. Use all poisons with care, keep them out of reach of children, and follow the directions on the labels.
Skunks. Skunks feed on bees at night by scratching at the front of the hive and eating the bees as they come out to investigate the disturbance. People rarely trap skunks for their pelts, and the animals are increasing in numbers in many areas. It is not unusual to find several in one apiary. The skunks weaken the colonies by eating large numbers of bees and are most damaging in the fall and winter after brood rearing has ceased. They also make the colonies mean and difficult to handle. If a colony suddenly stings more often and more bees fly around your veil, look for scratching in the soil at the front corners of the hives. Where skunks are numerous, they may dig enough to leave a trench in front of the hive. Their presence can also be detected by fecal pellets that are composed largely of honey bee remains. Control skunks by trapping or poisoning them according to recommendations of your county agent or extension adviser.
Other pests of bees. Ants, toads, bears, birds, dragonflies, and other animals prey on bees. Ants can be controlled by treating their nests with an approved insecticide. Such materials are generally highly toxic to bees and should not be used close to the hives. Single colonies can be placed on stands or benches protected by oil or sticky barriers. The other pests are generally not a problem in the Midwest. However, purple martins eat bees as well as other insects and may weaken colonies in areas where there are large numbers of nesting sites. Woodpeckers and flickers sometimes make holes in hives.
Human beings are often a serious pest of bees kept in outapiaries. They may tip the hives over with their cars or by hand, shoot holes in them, or steal honey and leave the hive covers off. Apiaries should be visited regularly to watch for such damage. The problem may be lessened by posting your name and address in the apiary in a conspicuous place.
Pesticides and Honey Bees
Toxicity of pesticides. Many materials that are used to control insects, weeds, and plant diseases are toxic to honey bees. These pesticides are placed in three groups in relation to their effects on bees. Highly toxic** materials are those that kill bees on contact during application and for one or more days after treatment. Bees should be moved from the area if highly toxic materials are used on plants the bees are visiting. Among the materials in this group are the foilsmang:
|Trade Name |
|Common name |
carbosulfan, FMC- 35001
Ethyl Gutbion, azinphos- ethy
*Short residual activity. Can usually be applied safety when bees are not in flight. Do not apply over hives.
Moderately toxic** materials can be used with limited damage to bees if they are not applied over bees in the field or at the hives. Correct dosage, timing, and method of application are essential. This group includes the following:
|Trade Name |
|Common Name |
|Abate, temephos |
Carzol, formetanate hydrochloride
|Larvin, thiodicarb |
Metasystox-R, oxydemethon- methyl
Sevin 4-Oil, carbaryl
The greatest number of materials are included in the relatively nontoxic group.** These pesticides can be used around bees with few precautions and a minimum of injury to bees. The following list includes some of the materials in this group:
Insecticides and Acaricides
|Trade Name ||Common name |
Bacillus thuringiensis, Bactur Bactospeine, Bakthane, Dipel,
Dylox, trichlorfon ethion
Heliothis polyhedrosis virus
|Mavrik, fluvalinate |
Sevin XLR, carbaryl
|Trade Name ||Comon Name |
|Benlate, benomyl |
copper oxychloride sulfate
cupric hydroxide, Kocide
Dithane M-22, maneb
Dithane Z-78, zineb
|Du-Ter, fentin |
Mylone, dazomet sulfur
Herbicides, Defoliants, and Desiccants
|Trade Name |
|Common Name |
|AAtrex, atrazine |
|Lasso, alachlor |
**Information extracted from Division of Agricultural Sciences, University of California, Leaflet 2883, February 1981, entitled "Protecting Honey Bees from Pesticides."
Pesticides damage colonies in several ways. Most often they kill the field bees without other effects on the colony. In some instances the bees die in large numbers after returning to the hive Many bees are also lost in the field and the colony is weakened but not usually killed. Sometimes materials are carried by the bees to the hive where they kill brood, young bees, or the entire colony. Encapsulated pesticides, such as Penncap-M, have this potential of being carried to the hive.
Methods of application. Losses from pesticides can be minimized by cooperation among beekeepers, farmers, and spray operators. Several basic principles should be followed to prevent losses of bees and to avoid injury to people and farm animals. The first of these is to apply the proper dosages and follow the recommendations on the label. The method of application is also a factor to consider. Ground application is generally safer than air application. The material and its formulation play important roles in its toxicity to bees. In general, sprays are safer than dusts, and emulsifiable concentrates are less toxic than wettable powders. Materials applied as granules are the least hazardous. At present there are no safe, effective repellents that can be used to keep bees away from treated areas.
Proper timing of applications of pesticides allows the use of moderately toxic materials on crops visited by bees. Bees visit different crops at different times and for different periods during the day. The timing of treatment of a crop should relate to these bee visits. Squashes, pumpkins, and melons are attractive to bees early in the day but close their blossoms in the afternoon. Afternoon and evening treatments, after the flowers close, are safest for bees. Sweet corn sheds pollen early and is visited by bees most heavily in the morning. Applications of insecticides to sweet corn are least dangerous when made as late as possible in the day, especially if the insecticide is kept off the tassels. For most crops, pesticide applications are safest for bees if they are made between 7 p.m. and 7 a.m.
The beekeeper's obligation. Beekeepers have responsibilities in preventing losses to their bees and in learning to accept some damage, especially in providing pollination services. In some areas, honey bee losses must be anticipated and the risk weighed against the possible returns from honey or pollination fees. Beekeepers should be familiar with commonly used pesticides and their toxicity to bees. They should know as much as possible about the relationships between their bees and the nectar and pollen plants in their territory.
It is essential that the owners of bees can be located easily when a nearby crop or the surrounding area is being treated with toxic mate- rials. Therefore, a beekeeper should provide his or her name, address, and telephone number to owners of land on which the bees are located. This information should also be posted in the apiary in large, readable letters. Beekeepers' organizations should compile directories of apiary locations and their owners in each county, and make them available, to- gether with marked maps, at the office of the county extension adviser or county agent.
Note: The above list of chemicals are quoted from the Midwest publication and should be considered 'historical'.