CHAPTER SIX
DISEASES AND PESTS OF HONEY BEES
As is true with every other living organism, honey bee colonies must deal with diseases and pests. Colonies that are generally healthy can withstand the occasional onslaught of disease pathogens, but they may become overloaded, and when this happens it is the beekeeper’s responsibility to take decisive action.
Some diseases and pests are worse than others. Varroa mites are a challenge to bee colonies in much of the world. Only recently, scientists have begun to explore the effects of the viral load that is transferred to honey bees by Varroa as they feed on the bees’ blood. The more established diseases, such as American foulbrood, are better adapted to bees and do not normally cause the devastation that an unrestrained Varroa mite outbreak can. The key to effective disease and pest control is in recognizing the signs early on and knowing how to deal with them. As the problems discussed in this chapter show, it is not always clear cut; the symptoms of some diseases are similar, and a colony may be suffering from more than one malady at once. With knowledge and experience, though, you can grow adept at reading the signs.
60 There are mice living in the beehive in winter
CAUSE
During fall months, mice begin to search for a suitable site for overwintering. Beehives—either empty or occupied—offer a protected wintering location. Dead bees, residual honey stores, and unused pollen are nutritious food sources for adult mice and their growing families.
SOLUTION
There are various reasons why the presence of mice in a beehive is undesirable. Mice agitate the bees, causing them to consume larger amounts of winter honey stores. When building nests, mice cut the combs and chew frame components in order to make a cavity. Additionally, the buildup of mice droppings creates an unwholesome odor. All of the above makes a very strong case for blocking any entrances that mice could use to gain entry to the hive.
In one way or another, all entrance reducers close down the hive entrance to 3/8in, which mice cannot get through. Some models also reduce the entrance width. The simplest procedure is to modify the bottom board so the bottom entrance is set to 3/8in (1cm) all the way across the hive front. Alternatively, a 3/4in (2cm) hive entrance can be closed down with a wood strip that fits tightly in the hive entrance and has a notch cut in the middle that measures 3/8in × 3in (1 × 7.6cm). Many beekeepers use a 4in strip of 1/4in hardware cloth, folded to 90°, that fits tightly on the hive front and the bottom board and completely covers the entrance. To prevent animals from removing it, this strip should be lightly stapled in place. While live bees can readily pass through this wire grid, house-cleaning bees cannot remove dead bees from the hive until it is removed in the spring. Commercially manufactured entrance reducers are available that are adjustable so they will fit any hive front and are easily installed.
These hives in Slovakia have the larger summer entrance reduced to 3/8in to prevent mice from entering the dormant hive during winter months. Another more modest benefit is that cold winter winds will be restricted.
61 There are multiple problems with the colony
CAUSE
During a difficult period, the colony can succumb to more than one malady. A bit of diagnostic expertise may be required of the beekeeper.
SOLUTION
Expertise in honey bee disease and pest identification can only come over time. While photographs and other educational materials are readily available, it is likely that you won’t experience a disease firsthand until it presents itself in your colony. If there are multiple problems, it can be even trickier to determine how to treat the ailing colony.
Competent disease recognition is absolutely necessary to maintain vibrant, productive colonies. Stay abreast of disease reports, discussions at meetings, and updates published in the beekeeping literature. Importantly, you should develop a cadre of beekeeper friends with whom you can discuss problems or ask for opinions. It is in their interest to help you, as bee diseases can spread to other hives in the local area if not dealt with effectively.
If you are new to the craft, regulatory or university staff may be able to help with a complex, mixed diagnosis. If the colony has time and energy, it may once again regain control of its own health. Bear in mind that while you are awaiting confirmation of the diagnosis, some of the earlier symptoms may fade.
Beekeepers should always be looking for problems—anywhere, even outside the colony. Inside the hive, watch for low-level problems and address them before they become major problems.
There are multiple problems with the pictured colony. There is a single Varroa mite in the upper left quadrant of the photo. The developed pupae (top, center) should not be uncapped at this time. Near the bottom center is a dead prepupa. There is a poorly formed queen cell near the bottom center of the photo and there are no uncapped brood or pollen stores for future uncapped brood. This colony could use some help.
62 Varroa mites have overrun the colony
CAUSE
Varroa (Varroa destructor) is a voracious external pest on honey bees in some areas. If left untreated, they can quickly build to population levels that can kill a populous colony.
SOLUTION
There is no chemical or management procedure that will completely eradicate this pest, so individual treatment regimes must be developed. One method is drone brood trapping. Drones require approximately 23 days to mature, while workers require just shy of 21 days. Apparently due to the longer development time, Varroa mites preferentially seek out developing drones. You can therefore use drone combs to attract mites away from other areas of the brood nest. Once the comb is filled and the drone brood is mostly capped, remove it and freeze it. Both drones and mites will be killed. The comb can be used again for the same purpose. During the warm season, you should perform this eradication procedure about every 18–20 days.
Manufactured chemicals are available to suppress Varroa populations. Most are applied on plastic strips that are hung between the frames, or as blotters that are laid on top of brood nest frames. Times and length of application will depend on the product, so follow the instructions carefully; always wear heavy plastic gloves and avoid inhaling the vapors. Chemical control materials should be rotated annually in order to minimize development of resistance, and integrated pest management should be practiced: mite resistant queens, drone trapping, and screen bottom boards should be used alongside.
Unless the product label explicitly allows it, do not use chemicals when honey supers are on the hive. Consider periodically replacing brood frames to avoid chemical residue accumulation.
The colony pictured has died from a massive Varroa mite infestation. The red tortoise-shaped mites are Varroa mites. A bee with deformed wings is present, indicating the presence of a pathogenic virus. This attack occurred during early September. The afflicted colony had no time to recover.
63 There are ants nesting beneath the outer cover
CAUSE
Depending on the ant species, some kinds of ant may actually nest within the colony. Other species live outside but near the colony. In general, beehive environs are good areas for ant colonies to set up housekeeping. There is a steady source of food from the hive and in some cases protection from weather.
SOLUTION
Ants can cause damage within the hive. Species that tunnel in wood, such as carpenter ants (Camponotus spp.), can damage equipment in a manner similar to that of wax moths; they are also reported to damage high-density polystyrene beehives.
As ants and bees are related insects, in general, any chemical insecticide that kills or repels ants will probably have the same effect on honey bees. Be very careful when using commercial ant insecticide near bees.
Cinnamon sticks and cinnamon powder are traditionally used by beekeepers as a repellent. No doubt this common food product will work at times, but not at others. Boric acid mixed with sugar or oil is frequently reported to work. The acid acts as an abrasive on the cuticular surface of the bee’s exoskeleton. Essentially, the insect loses its ability to retain moisture. However, if they are not protected from the concoction, bees will experience the same harmful effect.
In years past, beekeepers sat the legs of their hive stands in cans of oil or water, in the hope that this would serve as a moat barrier. Sometimes it did, but at other times the ants devised ways to bridge over the moat with leaves or twigs.
These are just some of the proposed methods for controlling ants in the hive, but none is universally accepted as the “best” way.
64 Small hive beetles have invaded the colony
CAUSE
The newest hive pest to establish itself in the United States (1998) is the small hive beetle (SHB, Aethina tumida Murray). Adults lay eggs in bee colonies. The larvae develop in large numbers, foul honey stores and combs, and stress bees. Bees frequently abscond, leaving behind combs and equipment that are difficult for the beekeeper to clean.
SOLUTION
This pest does not universally affect all beekeepers in all areas. In its home range in sub-Saharan Africa, it is not considered a major pest of honey bees. Research efforts have not yet produced an effective chemical control.
Various traps have been developed that do successfully harass the SHB, though they won’t eradicate the problem completely. These traps work in two ways: they form a tight space, which the beetles prefer because they feel safe from bee attacks in confined areas; they are filled with vinegar, which acts as an attractant and may also drown some of the adult beetles. Two traps are usually placed between brood frames near the center of the nest for each brood box. The lightweight plastic traps fit flush between frames and are easily installed, and can be discarded when filled with dead and dying beetles.
The only chemical controls are GuardStar™, which is applied as a ground drench in combination with Checkmite™ strips placed beneath pieces of corrugated board. Beetles hide beneath the board and come in contact with the strip, which has coumaphos as the active ingredient.
Beekeepers have reported that beehives in the sunlight survive better, but managing bees in the hot summer sun is uncomfortable. The best control advice is to keep the hive healthy and strong, keep the bottom board clear, and don’t disturb the bees more than necessary.
65 There are signs of AFB in the hive, but no foul odor
CAUSE
Bee parasitic mite syndrome (BPMS), a Varroa/virus interaction, looks very similar to American foulbrood (AFB), but without the foul odor and oily-looking cappings. It is caused when a large population of Varroa mites overruns a large bee colony.
SOLUTION
A colony experiencing bee parasitic mite syndrome (BPMS), a Varroa/virus interaction, is most likely doomed. Virus particles that have always been associated with bees have found a much improved transmission route with Varroa. Varroa does not always kill bees and brood, but it does weaken them. Varroa-assisted virus transmission has upset the evolutionary balance between the viruses and its honey bee host. The virus infection causes more damage than Varroa feeding damage.
The only solution is to prevent the mite population from reaching such high levels within the colony in the first place. Keeping mite populations reduced within the hive and performing these control procedures in timely and systematic ways is the best way to prevent BPMS. There are multiple control procedures that will suppress Varroa populations, but none will eradicate the pest.
Common methods for sampling the current population of Varroa mites are: sticky bottom board screens, ether rolls, or sugar shakes. Each method will yield an estimation of the number of Varroa contained in the sample. It is difficult to present the standardized threshold number at which point the beekeeper should initiate treatments. Speak to fellow beekeepers about the local threshold number.
BPMS strikingly resembles American foulbrood. Some adult symptoms are: Varroa mites are obviously present, crawling bees, littered entrance board, and a spotty brood pattern. However, the dead larvae do not rope out, scale is not brittle, and it has little odor. American foulbrood has an obvious odor and the cappings have an oily appearance. Additionally, scale will be brittle and firmly attached. Importantly, the comb can be reused, but American foulbrood combs cannot.
66 Chalkbrood is affecting colony productivity
CAUSE
Chalkbrood is caused by the fungus Ascosphaera apis. The disease is found essentially worldwide.
SOLUTION
Severe Chalkbrood infection results in the dramatic decline in productivity within the afflicted colony and reduces the adult bee population. Even if the colony recovers, it will not thrive during the remainder of that season. The time-honored solution to Chalkbrood is to requeen the colony, thus giving the colony enough of a brood break to remove the diseased contaminants from the colony. It is also thought that the new queen’s stock will provide more genetic resistance. It remains unknown how often a colony is actually improved by this procedure, but there is little else the concerned beekeeper can do. A few beekeepers have reported dramatic declines in the occurrence of Chalkbrood in irradiated equipment; however, most do not have access to such a facility.
Chalkbrood spores are remarkably persistent and may remain viable for 15 years. The spores can be spread from hive to hive by bees that are either drifting or robbing in combs and equipment that the beekeeper provides to the bees. These spores seem to be present nearly all the time and are not expressed until proper conditions are met. Moisture is a commonly accepted condition that encourages the appearance of the disease, but it is readily apparent in hot, dry climates, too. It is therefore vital that beekeepers do what they can to guard against the spread of spores. Wipe the hive tool and smoker with a disinfectant to prevent transferring spores to uninfected colonies. If possible, don’t use your gloves when inspecting an infected colony and clean your hands afterwards. Monitor frame exchanges so that nearby colonies are not exposed to fresh Chalkbrood spores.
Mummies quickly pile up around the hive front. Inside, on the bottom board, large numbers of hard, darkened mummies will also accumulate. Each of these hardened pellets is the remnants of a honey bee that died during development.
67 Wasps are attacking the bees
CAUSE
Dead or dying bees are a tempting food source for wasps. The entrance design of most beehives does not help to discourage their feeding habits.
SOLUTION
For most beekeepers, seeing yellowjackets (Vespula spp.) rip into bees at the front of the hive is unnerving, but normally, when compared to other pests and diseases, of little consequence. These insects are using the dead and dying bees at the entrance and on the landing board as a food source for protein. In the United States, it takes until midsummer for the populations to reach large enough numbers for beekeepers and homeowners to begin to notice them. They remain active until well into the fall season, and, depending on the climate, can even overwinter to form large nests. In some species, multiple queens add to the wasp population growth. If the climate is warm and winters are mild, these large nests can pose a more serious threat to bee colonies than wasps wintering in colder climates.
This behavior can become a more worrying issue when raiding yellowjackets are emboldened to actually begin to enter the honey bee colony, where they will be attacked by colony defenders. If a colony is weak or small, as in the case of a nucleus hive, bees will have much more trouble defending themselves. In addition to eating adult bees, in some instances wasps will rob honey stores and disturb the wintering colony. The only real solution is to relocate the colony entrance or reduce it.
68 Animals are visiting the apiary at night
CAUSE
The brood and honey stores in bee colonies have always been in demand by any animal that can gain access to the larder. The reward for the thief is high quality food that comes at a painful price. In particular, vermin and birds desire the dead and dying bees that accumulate at the hive entrance.
SOLUTION
This issue has particular emotional ramifications for many beekeepers. They want to keep their bees healthy and productive, but wildlife may continually harass the colony. It is not uncommon for such colonies to be cranky during daylight hours. Animal excrement, packed with bee parts, may litter the area, or if a skunk has visited, the area may still have some of the scent associated with that animal. Muddy prints may remain on the hive front or on the landing board.
Raising the entrance higher from the ground or improvising various barriers may deter animals, such as rolled 8in (20cm) diameter chicken wire placed at the entrance. Animals do not like standing on an unstable structure and the wire allows defensive bees to sting their underside.
For those individuals prepared to go to greater extremes, live trapping may be considered. All local ordinances and trapping regulations must be followed. Due to concerns about rabies in the United States, mammals cannot be routinely trapped. Clearly, if use of a firearm to control animals is chosen, all relevant regulations must be obeyed.
For most beekeepers, a more acceptable approach is fencing or even electric fencing. The initial expense is greater, but once an effective barrier has been established, future vermin visitors will be excluded.
69 The brood smells foul and has punctured cappings
CAUSE
A sour smell and ragged punctures in brood cappings are common characteristics of American foulbrood. It is caused by a bacterium, Paenibacillus larvae, that produces spores that are tough and can remain viable for many decades.
SOLUTION
American foulbrood (AFB) disease is feared and respected by most beekeepers—and it should be. A colony with more than a few cells of AFB has a poor chance of recovery. The traditional solution is to destroy the infected hive and the bees. In this radical way, the remainder of the colonies in the yard are protected from exposure caused by robbing and drifting bees. Not surprising, beekeepers are frequently reluctant to employ this radical procedure, but if all combs and contaminated honey are not completely destroyed, healthy bees in neighboring colonies are put at risk.
Where legal, antibiotics can be used to eliminate the vegetative stages of American foulbrood. Following the label rates for quantities, antibiotics can be applied as a powdered sugar/antibiotic mix on outer edges of brood frames. Generally, it should be applied three times at three-day intervals and will suppress the increased development of the disease. However, when the treatment ends, AFB will commonly re-occur.
Another traditional technique requires shaking all the bees from infected combs onto new frames and wax foundation. The bees are forced to rebuild the combs and without brood to feed, it is thought that their feeding glands are purged. Again, if antibiotics, such as Terramycin or Tylosin are permitted, these broodless bees can also be treated.
Beneath ultraviolet light, American foulbrood scales will fluoresce and show up as light blue. The infected equipment can be unknowingly stored away—sometimes for many years—possibly to be sold cheaply at auction. The combs, much more than the wood, will still contain spores that have the potential to once again blossom into a new AFB infection. If the history of old equipment is unknown, be careful when purchasing it.
70 Wax worms are destroying the combs
CAUSE
The greater wax moth (Galleria mellonella) and the lesser wax moth (Achroia grisella) are two premier lepidopteran bee comb degraders. The damage occurs during the larval stage as the larva tunnels through combs in search of protein from pollen and cocoons predominantly in the brood nest. An unusable morass of silk webbing and frass remains in the comb remnants.
SOLUTION
One of the unintended aspects of modern apiculture is the development of food resources for wax moths. A beekeeper’s storage building, with stacks of hive bodies filled with combs, provides massive food resources for adult wax moths. Comb destruction is severe and cleanup is laborious.
Paradichlorobenzene (PDB) has been used for many years as a comb fumigant. Boxes are stacked 5–6 feet (1.5–1.8cm) high, the bottom is closed off, and all joints are taped. Six ounces of PDB crystals are placed on a paper pad on frames at the top of the stack, and an outer cover is placed over this. The crystals need to be replaced every six weeks.
Wax moths do not tolerate sustained coldness well. Equipment can be frozen to eliminate the moth. Since this insect causes extensive damage to stored combs or to combs in weak colonies, other fumigants and procedures have been reported to be useful. Even so, combs—especially brood combs—cannot be left unprotected.
In the United States, the wax moth cannot overwinter in the northern tier of states. Depending on the season, the moth regains lost territory each year only to lose it again as the weather cools. Beekeepers in warm climates must deal with this pest year round.
