How Disease Can Cause Bee Population Decline

Facts About Honey Bees and Disease

How Disease Can Cause Bee Population Decline

By Jerry Hayes – How are you doing with your beehives? Have you gained some confidence? If you have, that is because you have made the effort to see how another species lives, and maybe you’re concerned with bee population decline. You have provided a space (hive) where they have built a home (nest) in a vast array of beeswax hexagonal cells. Maybe you’ve even started learning how to make your own hives from bee hive plans. You have seen eggs, larvae, pupae, and adults as they transition from life stage to life stage in these cells. You now know what a queen looks like.

As the only functioning fertile female and the mother of all the others in a “colony” these highly developed social insects are precariously balanced and dependent on this “queen.” All of the workers that make up 90% of the individuals you see are females but have not been produced and nurtured to be reproductive. These workers go through assignment levels in the colony based on age from feeding and caring for young, to house cleaning, hive repair work, to guard protectors, and lastly to foragers who risk themselves outside of the hive to bring back food (nectar/pollen) that is stored and preserved as honey and bee bread.

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Don’t the bigger, bulkier drones (males) with their huge eyes look out of place among the workers? Drones have half the chromosomes (haploid) as everyone else which makes them weak and fragile. They are just flying gametes (sperm) that are simply a delivering mechanism of genetic material if they get an opportunity to mate with a virgin queen outside the hive. Drones are produced, nurtured, and fed until environmental resource conditions preclude the colony taking care of them and preserving them. When things get tough, like in conditions that cause bee population decline due to disease or other environmental factors, the drones are the first to go. They are expendable. More can be easily made when things get better.

The reason you can see all these really cool things in a beehive is that Rev. Lorenzo L. Langstroth was paying attention when looking at honeybee colonies in the 1800s. He noticed that honeybees would leave gaps or not connect various hive parts such as comb and hive sides if there was a certain distance maintained. If this distance was too large the colony would build cross structures to bridge the gap and if it was too small they would connect them together as well. But if there was a gap of approximately 3/8 of an inch then this distance would be left open with few or no bridging attachments.

This “discovery” by Rev. Langstroth was called “bee space.” Maintaining “bee space” in your man-made wooden hive allows you to manipulate the frames that contain the comb that makes up the honeybees’ nest easily. You, the beekeeper, can now look at the nest which contains developing baby bees (brood) to check on the health and vitality of the brood and how well the queen is laying eggs. This “discovery” revolutionized beekeeping. Before this, the whole colony had to be killed to harvest honey and the condition of the colony was just a guess. Beekeepers could now be partners and managers of honeybees. You are the recipient of Rev. L.L. Langstroth’s ability to visually discern how a honeybee colony worked and then translate this into information that could be adapted for man.

Honey production increased remarkably with the improvement of beekeeping supplies like movable frame colonies because brood chambers (boxes) could be segregated from honey supers and frames, or whole supers removed without damaging the rest of the colony. Honeybee colony disease control, requeening, splits, divides, two queen colonies, and just about every other management technique to benefit the beekeeper and prevent bee population decline is dependent on movable frame colonies. Thank Rev. Langstroth for the next time you open your beehive.


With movable frame colonies, beekeepers discovered pests and diseases that they only superficially knew about. Honeybees, like any other animal, are subject to the frailties of this sometimes pale existence. They can get bacterial, viral, and genetic diseases, and get stressed from exposure to environmental and agricultural chemicals that challenge their immune system and can contribute to bee population decline. When the colony gets weak from pests, diseases or chemical stresses, there are other animals which can live on the contents in a hive that the bees can’t protect. Eggs, larvae, pupae, adult honeybees, honey, bee bread, and old beeswax can be food for other animals. It is a rough world out there. (Or maybe it is just normal and we see with different eyes.) This laundry list of potential challenges is for your awareness, not for your fear. You can take steps to prevent bee population decline once you know what to look for and how to treat these bee diseases. Remember what I said in earlier articles and stay calm – there will be plenty of time to panic later.

Bee Diseases – American Foulbrood Disease (AFB)

spotty foulbroodAmerican Foulbrood disease (AFB) is caused by a bacteria Paenibacillus larvae. A spore-forming bacteria, it infects larvae less than 53 days old. Older larvae are immune. Spores only can infect the larvae. After ingestion, the spore germinates and a new active form of the bacteria multiplies in the midgut (intestine), penetrates into the body cavity through the gut wall. The larva ultimately dies, causing a bee population decline in your colonies.

Healthy larvae are pearly white. When infected by AFB the color changes to a dark brown and finally black. In the brown stage, the decaying remains take on a gooey, thick, mucousy condition. If one sticks in a matchstick or toothpick and pulls back, the remains will be stringy like hot cheese on pizza. In the final black stage, the remains are called “scale.” They are very hard and crusty and contain millions of spores, ready to infect.

american foulbrood ropiness

The only true way you can control AFB is to burn the comb in a fire. Many will tell you that feeding antibiotics to the bees will stop the disease, but because the bacteria are spore-forming, when confronted by antibiotics the active bacteria forms this indestructible spore that is protected from just about everything. A few years ago the USDA tested the viability of AFB scale they had collected in the 1940s. Under the correct conditions of being ingested by a honeybee larva, they germinated and were able to infect bee larvae even after over 60 years. A beekeeper can stop the active bacterial stage by using antibiotics, but ultimately it will be for naught because AFB is a survivor that uses a spore to survive indefinitely.

Your treatment options for AFB is to either burn any affected frames or use queens bred for hygienic behavior that will reduce the spore load as house cleaning workers clean out the dead and the dying before they build up into a vast spore reservoir and contribute to a bee population decline.

European Foulbrood

European Foulbrood (EFB) is another brood disease. It is caused by the bacteria Melissococcus Pluton. This is not a spore-forming bacteria but it can persist in a colony in the remains of the dead if the bees are not hygienic enough to remove the residue, or in feces that may accumulate in cells of developing bees. This disease usually, but not always, appears in early spring and many times disappears until sometime the next year.

EFB can cause bee population decline in a colony but seldom kills the colony outright as may happen with AFB. The larva color will change from pearly white to a brown and then black, but the remains are not stringy, just mushy. Antibiotics are labeled for control, but good overall colony health and EFB’s self-limiting nature based on early season stress should preclude the use of chemicals. Many times re-queening allows time for a new queen to take over and diseased remains to be removed.

Honey Bee Parasites:

Varroa Mites

Varroa Destructor can cause rapid bee population decline. To get an idea of the magnitude of this honey bee parasite, make a fist and place it on any part of your body. This is how large proportionally that the Varroa mite is to the honeybee’s body. This mite sucks the honeybee’s hemolymph (blood) and obviously weakens bees in any part of the life cycle. The varroa mite also vectors or transfers viruses which can additionally weaken and deform the wings of the bees so they cannot fly.

Varroa mite is an introduced species from Asia. It is actually a mite on an Asian bee, Apis Cerana, that has made the jump to Apis Mellifera, the honeybee that you have. As a new parasite on a new host, it is not a very good parasite in that it kills its host. If varroa mite populations are not kept in check in a honeybee colony that colony will be dead in two years.

There are a variety of ways to kill and disrupt the varroa mite’s life cycle and eliminate them from a colony. In your beekeeping supply catalogs go to the page that has screen bottoms. The bottom or floor of a beehive in the past has usually been a solid wooden structure called a “bottom board.” One strategy to reduce the varroa population and prevent bee population decline in your colonies is to use a bottom that is made of screen or hardware cloth instead of a solid board. Varroa mites, when they emerge from honeycomb cells after reproducing, grab an adult to ride on or try to scurry across the comb to another area. This is a pretty precarious action and results in about 40% of the time the mite losing its grip or footing as the case may be, and falls to the bottom of the hive. If they fall to the bottom of the hive on a solid bottom they can pick themselves up, dust themselves off, and start all over again. If they fall to a screened bottom open to the ground, they find themselves on the ground and they have a vast distance to try to traverse to get back into the colony and usually die or are eaten by something before they make it.

Screen bottoms are fine to use all year round. Yes, they are open to the environment but if the correct size mesh is used only varroa and other small stuff falls through and nothing else big can climb in the hive. Don’t worry about the winter cold. If your colony is out of the wind, cold does not kill honeybees if the colony is healthy and has food stored. The colony does not heat the whole hive in winter, only the cluster. When it is zero outside it is zero inside the hive, except at the cluster which keeps its interior at about 93°F.

Chemical control of varroa mite has become the accepted method of partial eradication. Nothing kills all pests 100% of the time—, and varroacides do not work 100% of the time, either. What has happened with varroa and miticides (chemical pesticides) is that when first introduced 97% of the mites are killed. That leaves 3% that are resistant for one reason or another to breed. Over a few years, varroa has now become resistant to the chemical. This has happened with two products, Apistan (active ingredient: fluvalinate) and Check Mite (active ingredient: coumaphos). These products do not control varroa consistently any longer.

To deal with the ability of varroa to develop resistance to standard miticides and pesticides, other products and management techniques have been developed. I’ll mention just a few of those that are safe and effective. Couple these methods and techniques with a screened bottom board and you have your own Integrated Pest Management strategy to help prevent bee population decline.

There is a product, Mite Away II, which uses a naturally occurring acid (formic acid), in high concentrations to kill or injure the varroa mites. When used according to label directions (which include outside temperature, colony condition, and humidity specifics), this product works well. It is a little hard on the queen but if only used once a year it is better than injuring and weakening of the colony by varroa. There is no chemical contamination or residue problem with this product.

Apiguard uses an essential oil, Thymol, from the thyme plant, again in high concentrations in a gel formulation to control varroa mites. The vapor released from this product kills or injures exposed varroa to release from their host and fall to the bottom of the colony and out onto the ground when a screened bottom is used. Because it also is an irritant to the bees they spontaneously begin active grooming of their sisters, which dislodges even more mites. This product does not have chemical residue issues when used according to label directions.

The most interesting, safe, and inexpensive method of varroa control to prevent bee population decline is the powdered sugar method. We have kept colonies alive and well going on six years now using powdered sugar. To give you a little background we maintain approximately 100 research colonies. These are used to investigate better, safer, more efficient ways of maintaining honeybees. Because beeswax is a “chemical sponge,” we need to know everything that certain colonies have been exposed to in the past, so our results are not influenced or skewed in new trials. For maintenance of colony health, all chemical treatments are out. Varroa mites have little special pads on their feet which allow them to hang on to the bee. If you dust the bees with a very fine powder such as powdered sugar, it gets on these foot pads and the varroa mites can’t hold on to anything. Everything becomes slippery. They fall to the bottom and out through the screen bottom and are gone.

Take a half pound of very fine powdered sugar or icing sugar and thickly sprinkle it over the top bars of the brood chamber. The sugar that doesn’t immediately fall between the frames and onto the bees should be brushed off the top bars and onto the bees. The bees will look white and dusty. It doesn’t hurt them and as it is sugar, in the process of cleaning themselves more mites are knocked off and they can eat the sugar, which is your varroa control product. No contamination, no residues, and it is safe for the bees and you. I think this is so cool. It is labor intensive, but for a small number of colonies (under 10), it is my preferred choice for varroa control.

tracheal mites

Tracheal mite (Acarapis woodi) is another parasitic mite that contributes to bee population decline, but this one lives within the breathing tubes or trachea of the honeybee. It weakens the bee by piercing the wall of the trachea to feed on hemolymph, leaving open wounds for secondary infections to start—. It also clogs the trachea with more mites, making it difficult for the honeybee to breath. This mite makes overwintering in cold climates difficult as the bees cannot breathe efficiently and sufficiently enough to maintain a warm enough temperature. A safe treatment for tracheal mites can be Apiguard in late summer as the Thymol vapors kill tracheal mites as well as varroa mites.

nosema spores

Nosema (Apis or ceranae) is a protozoan parasite that lives in a honeybee’s intestine. When honey bees are confined for a long period, such as in winter, they still eat and do all biological functions except fly outside to defecate. They have to “hold it” until the weather warms enough to leave for a cleansing flight and then return to the colony. Darker honey is darker because it has “indigestible” stuff in it. This indigestible stuff builds up in the honeybee’s intestine and acts as a food source for the protozoan. Then the protozoan starts affecting the lining of the intestine and causes the bee to lose control and have diarrhea inside the hive. Honeybees do not normally defecate inside the hive but they can’t control themselves. The feces have more of the Nosema organisms in it and when this happens it spreads the disease very quickly, causing serious bee population decline in the colony. The organism is all over the inside of the hive in the feces and readily infests other colony members.

Be aware of the “quality” of the honey stored. The lighter in color the better. It may not matter if the bees get a cleansing flight every four to six weeks to relieve themselves. There is a product called Fumidil which can be fed in sugar syrup in the fall which effectively kills Nosema.

wax moths

Wax Moths are moths that can use a weakened colony or stored equipment to raise its young on the beeswax comb. The wax moth adult female sneaks into a colony that is weak and can’t protect itself, usually at night and lays eggs in cracks and crevices. The eggs hatch into very small larvae which start tunneling into the interior of the beeswax comb. They feed on larval skins left behind in the brood cells, pollen and other protein that the wax moth larvae need to develop into an adult. Big, strong, populous healthy colonies are the best preventative to wax moths. In stored equipment in summer months, using paradichlorobenzene, PDB, as a chemical control can work. In stored equipment, winter-cold temperatures are a great control for wax moths.

small hive beetle larvae

Small Hive Beetles (SHB) are a relatively newly introduced pest from South Africa. These are like wax moths on steroids. SHB are looking for a safe, secure, and food-laden place to raise their young and continue their species. The adults, which are 1/8 inch oval, dark brown or almost black, are not the problem. It is the children that are the concern. The SHB females will pick out a honeybee colony which is in stress and does not have enough bees to cover every square inch of comb to police and protect it. The honey bees, which usually can grab an intruder and sting them and or remove them from the colony, can’t do this with SHB adults. The SHB adult is like a little oval smooth tank. The bees can harass and chase the SHB but can’t grab or hold them. There can be hundreds of SHB adults in a colony seemingly doing no harm. The honeybee colony weakens even more and then at some tipping point all of the female SHB lay their eggs in unison.

A female SHB can lay up to 500 eggs per day. Multiply this by several hundred females and that is a lot of eggs. The eggs hatch in 24 hours. The thousands and thousands of larvae start feeding on honey, bee bread, honey bee larvae, pupae, and adults, contributing to bee population decline in your colonies. The bees are overwhelmed and many times what is left of the colony simply leaves en masse. The thousands of larvae have a slimy mucous associated with them and the whole interior of the hive can get covered in this mess. It is not pretty.

The best preventative for SHB is a big strong colony that can defend itself. If it doesn’t look like an SHB nursery, it won’t be. There is a bottom fall trap that can be put on a colony to catch and kill SHB that is pretty effective, but (and there is always a but) SHB adults are pretty good flyers so one can catch a lot of SHB in the bottom trap and if the SHB sense an opportunity to use this colony in the near future for a nursery they will fly in. Having fewer SHB adults is a good thing, but there may be a never-ending supply in the environment, depending on where you live.

If this list of potential pests and diseases doesn’t scare you off then you have caught the vision and the excitement of honeybees. There are other minor fungi, virus, and predator problems but you can research those on your own. I hope the message on diseases and pests that you got was one that good strong colonies and rational use of chemicals is the answer to keeping good strong colonies and preventing bee population decline. This will not be perfect in a less than perfect world where bee population decline is a problem, but now you know. Knowledge is power.

Honey Crop

liquid honey

The honeybees we use in North America are an insect that is adapted to a temperate environment—, a climate that is marked by seasons. The most important season is winter, because it can mean the difference between life and death, and plays a big part in bee population decline from disease. Honeybees are in effect always preparing for winter. Their life cycle is such that the colony population growth in spring and summer is to maximize nectar collection in order to store as much food (honey) as it can in anticipation of months and months of a dead environment (winter) devoid of flowering plants producing nectar and pollen.

All other things being equal, honey bees can collect 100 to 200 pounds of honey in the northern tier of states and 200-300 pounds in some parts of the southern states. Healthy honey bees generally only need 50-60 pounds of honey at a minimum to make it through a typical winter. This leaves a surplus that the beekeeper can harvest without affecting the colony negatively. This is agriculture at its fundamental best—help nature and it gives a surplus, which goes back into the cycle of life. Pretty cool.

Beekeepers who partner with their honey bees to assist them in health and vitality (and help prevent bee population decline) will be rewarded with surplus honey whether they want it or not. Sometimes lots of honey. As long as the bees have their basic food needs met for winter the beekeeper can harvest as much or as little of this surplus as they need, want or desire.

Honey is the end product of the honey bees collecting nectar, the sweet sugary offering made by flowering plants to attract pollinators. Honey bees add enzymes to the nectar to change the composition and ratio of sugar in the nectar. Then this nectar is deposited in honeycomb cells. The colony evaporates the nectar’s high water content down to 18% moisture (or less) by creating air flow. At this moisture level, the honey can be stored indefinitely as other organisms cannot exist in this dry environment. Honey has been found in tombs in Egypt after thousands of years of storage. Honey does not go bad or spoil unless the moisture level rises. Sometimes the ratio of sugar in the honey may cause it to form sugar crystals and the honey becomes a semi-solid, but this is normal and is the preferred form of honey that most of the world likes to eat.

Every flowering plant produces a different kind of nectar. Appletree flowers produce different nectar than clover, black locust, dandelions, sweet clover, etc. Honey made from one source is almost like a varietal wine made from a certain grape from a certain year from a certain region. When I was a beekeeper in the mid-west my goal was always to try to have my colonies in a prime condition to collect nectar from a stand of black locust near my home. About every third year I could do it. The other two years the weather changed and froze the blossoms or we had a windy storm which would blow the blossoms off the trees. But in the year I could I was pretty excited. It was fun, almost like a risky goal that was not by any means a sure thing but obtainable if I had everything right.

Whatever honey you and your bees produce, whether from one primary source or from the bees mixing nectar from different sources together to give you a natural blend, it is wonderful! It will taste better than anything you have ever had that called itself honey from the store. It will be fresh and pure and will remind you of flowers and spring or summer and will bring back memories of the whole season.

I will let you decide if you want to produce comb honey or extracted liquid honey and the beekeeping equipment needed to do that. All the parts and pieces are in the catalogs so I will not belabor that here. For a new beekeeper, just taking a perfectly white capped frame of honey out of your first colony and digging your finger into the honeycomb and taking a quick taste of this incredible flowering plant/insect collaboration makes it all worthwhile. It may be one of the most fun things you will ever do. You have made a connection from a botanical environment to the insect world to man, and maybe did something to help prevent bee population decline. It is amazing and very few, in fact too few, on this earth can claim this connection. Beekeepers are unique and special and wonderful, too.

Originally published in 2007 and regularly vetted for accuracy.

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