Bee Pests and Diseases
DISCLAIMER: Every bee-keeper approaches management of pests and diseases differently. I will outline the major pests and diseases common to bees, particularly those commonly found in our region. I will then offer different management techniques for dealing with these pests and diseases and my personal bee-keeping philosophy regarding this issue.
Varroa – this is a parasitic mite which was imported from India. It feeds on brood and multiplies in capped cells. In large infestations, adult mites can be seen on adult bees. However the best indication of whether varroa is a problem in a hive is to pull out some drone brood with a cappings scratcher or a fork, and see if there are any mites on the brood. Mites prefer drone brood because it is larger and the cells are larger. Mites are a reddish brown color and are about 1 mm in diameter. Intervention – Varroa intervention has become quite a controversial topic among bee-keepers. Chemicals, both organic or not can be placed on the hive to kill mites. These chemicals MUST only be used when there are no honey supers on the hives. It is against the law to have any kind of chemical treatment, organic or not on the hives during honey flow. Other treatments include: Powder sugar dusting, using drone brood comb as a trap, screened bottom boards, and sticky boards.
Tracheal mite – These mites infest the trachea of the bees. They have no outward signs, so they are difficult to detect without dissecting dead bees and examining the trachea for damage. Intervention – Chemical treatments for varroa are also effective against tracheal mites because they are both mites.
Small hive beetles – These do not survive our winters, but have been increasing in our hives in recent years. They are small black beetles that like to breed in the comb and make a mess of everything with their frass. They destroy comb and leave a slimy, smelly mess all over the hive. Some of them hitchhike in packages. They can also fly from apiary to apiary and spread that way. Intervention – placing beetle traps in the hive, sticky boards, oil traps and screened bottom boards.
Wax moths – These moths feed on the larval skins and wax, mostly in brood comb. There are two kinds, the greater and the lesser, but both will completely destroy empty comb by spinning cocoons in the comb, leaving web trails and eating the wax. Intervention – keep a close eye on hives and remove empty boxes promptly, or combine weak hives, or boxes so there are not a lot of empty brood combs in the hive for them to infest. When storing empty comb, put moth balls in them, just be sure to air them out very well before using them again.
Mice – They move into empty boxes that have been vacated when the bee cluster moves up in the winter. They chew up comb, fill the empty space with their nest and all their “waste” which basically ruins several frames, usually in the middle of the box. Intervention – place mouse guards on the hive entrances and make sure none of the openings in the hive are larger than 1/2 inch in diameter.
Ants – Most ants in this region are really not a problem, just a nuisance. The sugar ants are attracted to the sugar water or honey you put on the hive for the bees. When the hive builds up sufficient numbers, the ants usually leave. In warmer climates fire ants are a problem, and bee-keepers have to place their hives on stands with cans of oil under the legs to discourage them.
Skunks – Yes, skunks like to eat bees, and apparently can tolerate their stings inside their stomachs. They will even teach their young how to raid a bee hive to eat bees. If you find foot prints or other signs that skunks may be visiting your hives, you can put a board with nails pointing up in front of the hive to discourage them.
Bears – No, I don’t know of any close to our area, but not too far north of here, they can be a problem. The only solution is to fence in the hives with bear-proof fence.
Nosema – is characterized by bee dysentery. The droppings left are like tobacco stains, not mustard color like normal bee droppings seen in the winter and early spring. A new strain of nosema, nosema cerana may not have the dysentery component, which makes detection more difficult. The traditional intervention for nosema is Fumagilin, which is fed in sugar water in the hive. This treatment has traditionally been done as a preventative measure, but some bee-keepers are questioning whether to treat something if it doesn’t currently exist.
American Foulbrood (AFB) – Characterized by discolored, sunken or punctured cappings in brood. The dead brood will be older sealed larvae or young pupae upright in cells. The dead brood will be dull white, becoming brown and almost black over time. The brood will be ropy. There will be an odor. AFB must be completely destroyed by burning all the comb and burning, or completely scorching the hive with a torch. AFB is very contagious and at one time it was the law that you must destroy your hives if you had it. AFB was the reason moveable frame hives were the only legal hives for many years in the US, because the frames could be easily inspected for AFB. Traditionally Terramycin or Tylan have been used as a preventative for both AFB and EFB.
European Foulbrood (EFB) – The brood will not usually be sealed. Some will be sealed with discolored, punctured or sunken cappings. This usually affects younger larvae than AFB. The brood will be more watery than AFB, and won’t be as sticky. It will have a sour smell. The frames will still need to be destroyed, but this is not as serious a disease as AFB.
Sacbrood – The brood will be sealed, scattered cells with punctured cappings, often with two holes. The dead brood will be grayish or straw-colored, which then turn grayish or black with the head end darker. The brood will be watery and granular with a tough skin that forms a sac. It is not always accompanied by a smell, if it does it is just slightly sour. Sacbrood does not spread and the only intervention is to try to strengthen the colony.
Chalkbrood – The dead larva will have a chalky white appearance, and will be mummified. There is no treatment for chalkbrood, a strong colony will remove the diseased brood, but a weak colony will be unable to do so and the disease will spread and overwhelm the colony.
Management for healthy hives
As the old saying says, “prevention is the best medicine”. A strong, healthy hive will be able to withstand the pressure of pests and diseases and will be able to keep these enemies at a tolerable level within the hive. Many of our techniques for controlling pests and diseases have focused on getting rid of the pest or disease, rather than strengthening the bees so they can fight them off on their own. By removing the pests and diseases, we have weakened our bees. They have been unable to develop resistance to their enemies because we have taken the enemies away. In the process, we have often stressed the bees by weakening them with the chemical treatments designed to destroy the pests. If we focus on strengthening the bees, rather than on eliminating the pests, I think in time they will develop a reasonable resistance which will allow them to live with tolerable levels of these pests and diseases.
Warning signs of a weak/stressed hive-Weak hives will have decreased activity noticeable even from observing the traffic at the entrance. Often you will see guard bees engaging in numerous fights at the entrance which indicates a lot of robber bees attempting to get in from stronger hives. You may also observe yellow jackets and other predatory insects entering the hive with little or no resistance, or find them inside the hive. When you lift the top cover, there may be ants under the cover. A strong colony of bees will not tolerate the ants. Inside, you will find a small number of bees. A queenless hive will have no worker brood, only perhaps some scattered drone brood. A strong, queenless hive will be defensive, but a weak hive may not be. A weak hive will have little or no honey stores and will have a smaller than normal number of bees for the time of year.
Causes of a weak hive:
Queenlessness is the most common cause of a weak hive. If the hive is re-queened quickly enough, it can be corrected.
Chemical over-spray – if a hive is located too close to a place where agricultural chemicals are used, it could be poisoned by overspray. Prevent this by choosing a hive location away from crops that are routinely sprayed, including orchards. If the hive is used for pollination, make sure it is removed as soon as the blossoms drop from the crop being pollinated, so it won’t get accidentally sprayed.
Swarming – If your hive swarmed, over half the bees and the old queen may have left. If this is the case, check to see if there is a new queen in place and that she is laying. The best prevention for this is to keep close watch on your hives and purposely split them before they get anywhere near having completed swarm cells.
Too much moisture/lack of ventilation – bees, like most creatures need a dry, well-ventilated environment. Make sure the hive is well ventilated and receives at least some sunlight throughout the day. Some research indicates a sunny location prevents small hive beetles and other pests. This can be accomplished by ventilated the top cover and using a screened bottom board year round. Don’t place your hives in a swampy area.
Too much human intervention – As bee-keepers, we are anxious to make sure our bees are doing well. However there can be too much of a good thing. If we disturb the hive too much, the bees may supersede their queen. Some research has indicated that small hive beetles increase with too much hive disruption because the bees guarding them go away and they escape. Bee-keepers should limit hive inspections to about once a month unless a check from the outside indicates something that needs immediate attention.
Drifting – Bees locate their homes by landmarks which are unique to their hive. If all the hives look exactly alike and are lined up in a perfectly straight row, they may drift to the wrong hive. Over time, one hive will become very strong and the others weak because all the returning foragers are going back to the one strong hive. Prevent this by painting hives different colors and arranging them at slightly different angles. Also try not to put too many hives in one location.
Lack of stores – A strong hive will make plenty of honey to overwinter, but we as bee-keepers may take off too much when we harvest and leave them with inadequate stores for the winter. Sometimes this is hard to judge, so we need to make sure we monitor them and feed them if necessary.
Trapped in the hive in the winter – The bees need to get out for occasional cleansing flights in the winter. If there are no alternative entrances to the main entrance and it gets blocked with snow/ice or dead bees, the bees will be trapped inside with no way to take cleansing flights and the hive will become soiled and quickly breed disease.
Damage due to storms, large animals, falling branches, etc. – Bee hives are remarkably resilient to being damaged, but have to be put back together quickly. If the queen was killed she needs to be replaced quickly. If there was young brood in the hive at the time of the accident, the bees will re-queen themselves unless the hive was too seriously disturbed. Try not to place your hives in low spots which are subject to flooding, or under large trees which could lose branches. Don’t place hives in an obvious deer run or by large holes which look like coyote or other animal dens.
Poor genetics – Occasionally you will have a hive that just won’t thrive no matter what the conditions. There isn’t much to be done in this situation. You can kill the queen and re-queen with a queen from a strong hive. Other than that, you really don’t want to propagate the poor genetics, so it is best to let nature take its course and practice “survival of the fittest”.