[Bonus] Colony Necropsy with Dewey (BSD-2)

[Bonus] Colony Necropsy with Dewey (BSD-2)

Hi, I am Dr. Dewey Caron. I again come to you from Cochabamba, Bolivia, where I spent part of the winter season with my wife's family and helping with the family's Africanized bees. I present another audio postcard in my new series of once monthly Beekeeping Today mini-series podcasts.

 Last month, I unveiled Bee Science with Dr. Dewey Caron. This is the second installment a series. Each episode will blend research, field experience, and seasonal context, focusing on the why behind honeybee biology behavior. I welcome your suggestions for timely topics. My mini-series topics this month is dead-out necropsy.

 Unfortunately, beekeeping means we frequently lose a colony. Each loss hurts. Examination of a dead colony can help determine what might have been the reason for colony death. Beehives are an ideal environment for harboring the growth of pathogens with abundant highly concentrated stored carbohydrates, that is honey, and proteins, the bee bread. Additionally, social organization fosters behaviors such as food exchange and thermoregulation, among others, and these aid in rapid pathogen growth.

 Bee colony death can be due to a number of factors, environmental extremes, specific bee pathogens, pest activity, pesticide exposure, external as well as internal, nutritional deficiencies, internal colony social dysfunctions, especially related to queen replacement, many in other words. Additionally, colony death can be caused directly or indirectly by the beekeeper, either doing something incorrectly or more frequently missing those signs, those symptoms, and are not properly intervening in a timely fashion. Success in beekeeping means mastering a steep learning curve.

 The majority of bee colonies are lost during winter. This is not to say colonies are not also lost during the active season. As for example, when a couple of weak colonies need to be united, or colonies swarm, supersede your or abscond and fail to properly then requeen. These common behaviors may weaken the colony enough that it fails to survive. The season is short, resources are not unlimited, and not all colonies are in sync with their real world. We should define when our colonies died over winter. Fall losses, that is losses prior to winter solstice, are usually the consequence of an event that occurred during the prior active season, such as pesticide poisoning combining two colonies or a colony queen event. The most likely reason for a sudden fall loss, however, is due to virus epidemics spread by varroa mites. That's the most likely reason. 

 Early spring losses, that is post winter solstice, also may be related to a previous seasonal event that weaken a colony. Wintering losses of spring colonies usually appear and are frequently attributed to colony starvation or poorly populated colonies, too small to survive. Smaller colonies, especially newly established colonies with insufficient drawn comb, such as a late season swarm capture, for example, or a split, may have had too little time to accumulate enough honey stores to enable winter survival, i.e. starvation of the colony of winter. The population may not have been sufficiently large enough to successfully cluster for warmth and support brood once it begins to expand in early spring, i.e. the cold killed the colony.

 Small scale, that is our backyard, our hobbyist beekeepers, individuals who keep fewer than 50 colonies, actually the averages of those over 50% have three or fewer colonies on average, they will lose about 40% of their overwinter colonies historically. Losses among sidelines those with 50 to 500 colonies, and commercial beekeepers owning 500 plus colonies, losses are not as high. The past two years, this has been reversed. Larger holding beekeepers have recently experienced percentage-wise heavier losses. Considering additional losses during the active year, it is shocking, but we find approximately one of every two colonies will not survive over a full year period. Colony losses of this recent magnitude are not unprecedented. The Reverend L.L. Lankstra, developer of the modern movable frame hive bearing his name, wrote in early editions of the Hive and the Honeybee that losses of 45 percent overwinter might be expected in some seasons. He believed the beekeeper should plan to take losses in the fall by combining and uniting to ensure only strong, well-provisioned colonies are overwintered. Additionally, unusually heavy, often sudden losses have been reported in some locations in some years. They are given names like Isle of Wright Disease, Spring Dwindling, Autumn Collapse, May Pollen Dearth, etc.

 These sudden fall or spring losses have been noted extending back into the 1800s in the bee literature. The show notes reference such a report. Prior to introduction and spread of tracheal and varroa mites in the U.S., annual losses of 5 to 10 percent were considered normal for North American beekeepers. Wintering losses were elevated to 20 to 30 percent in 2006 and the 2007 winter, as documented in the first national bee informed survey. Then they have increased. Based on the 2018-19 bee informed partnership survey, the annual overwintering loss across the U.S. was 37.7 percent. And I found them to be 48 percent for small scale beekeepers in the Pacific Northwest that same year. Currently, that is 2025, our last winter season, losses are apparently higher, exceeding 50% to as high as 90% annually for three of the past four seasons, or according to the Auburn University and Oregon State University survey data. That's the successor to the BIP National Survey. You can use a search engine to find reports of these losses.

 So now let's get on to our dead colony necropsy. What can they tell us? During a dead colony analysis of beehive necropsy, it is not a precise science and determination of the reason for colony failure is not always possible. Examination of a dead colony might help eliminate some possible causes, result in a probable diagnosis or a shorter list of different diagnoses. The real value is then this knowledge can trigger management changes in a subsequent season. Dead colony examinations start outside. First, examine the entrance area of the hive and immediately around the front of the colony for dead bees or brood.

 Some dead adult bees and or dead brood will be normal in front of the colony and sometimes on the landing board at the entrance, especially early in the morning or on a cold day. You need determine if you are seeing excessive loss. The hive bottom board can yield some information but checking it may be difficult with some types of hives. It usually will mean removing boxes to excess. If your bottom has a screen bottom board with a debris board below that screen bottom, examine it. This garbage pit beneath the hive where debris falls has a tale to tell.

 You need become familiar with ordinary hive debris to determine if the material observed is abnormal. The debris board will tell you the approximate size of the winter cluster, which will be valuable. The upcoming Beekeeping Today podcast will also be helpful as we have Ray Baxter, who will be talking about his book, Bottoms Up, about this hive debris. Fascinating what he has been able to learn with a year's examination of what falls in below the bottom of a hive. Be sure to listen in.

In virtually all instances, it will be necessary to open a colony and look inside to diagnose reason or probable reason for winter loss. Start with removal and examination of the two covers. Determine of covers frames are water stained, have signs of water condensation, or be fecal waste staining, especially on the top bars. These signs can help in your diagnosis of reason for loss. They signify that the top insulation was not adequate and perhaps moisture was affecting the bees over the winter and wet bees do not do as well as those that remain dry. 

The most revealing evidence will be dead adult bee bodies on the cold face. Some bodies may be scattered and on a bottom board will also have some dead bodies, but you should locate the remains of what was the cluster. Are there worker bees headfirst in cells beneath the dead adult clusters? Is there a non-emerged brood? Look immediately about the cluster in another comb. Some of the capped brood may be torn open. This is from bees attempting to cannibalize their young. If brood is just where you found the cluster, this is important to note. 

Observe evidence of honey stores, but be aware that any remaining honey may have been robbed by bees from other colonies in the vicinity. And this will look like very ragged cells. They're not very good in uncapping cells to get at the honey. They're in a hurry. The brood pattern is a key diagnostic for the size of the colony in healthy bees. In a dead colony, brood remains can be used to estimate the former size of the colony. 

See if the dead brood is mainly near or beneath the cluster and not found in other frames. Look for signs of active or remains of past queen rearing. Queen cells are distinctive in being vertically oriented and they will last a while after queens have emerged.

Now let's zero in on the three major factors in non-survival of a winter colony. Too small a population, starvation, and virus epidemic. The last factor is often a contributor to the colony loss of a weak colony and also frequently to a starvation loss. Our necropsy will help determine the probable reason for our loss. So, a weak colony. County adult population size and the amount of brood in a colony are relative. A weaker colony will have a smaller brood rearing area, perhaps not larger than softball in early spring. And here early spring is simply defined as when brood rearing begins or when you're first looking in your colony. Sometime January for you, maybe February. Maybe only on a single frame or in a small limited area on two to three adjacent frames. whereas a larger colony may have a brood area of basketball size or larger with brood on four to five parallel homes. 

In normal development, the spherical brood area will expand in spring to adjacent frames, growing to the size of a beach ball or exercise ball within a generation or two, depending on when you're looking, environment, et cetera. Weather permitting, the collection of resources, the genetics of the queen, the amount of resources stored in the previous fall, the health of the brood and adult bees, and of course, the winter survival size are all important features that will impact how fast a colony will grow and its subsequent size. 

Small colonies, along with newly established colonies, such as from package or nukes, can die from lack of proper initial care. But small colonies also can survive. Signs of loss from too few bees include a handful or more of dead bees on the bottom board and or a small dead cluster with some workers head first, that is tails out, cells around a small patch of dead capped brood located on one or most two brood cones. Those capped brood may have been opened, cannibalized. Mold may be evident in cells of bee bread. If the bees are wet, fly maggots can be common. Determination of too weak is relative, And external weather, such as a cold snap, often so common in the spring, are often a mitigating factor. 

The second reason I mentioned for the major losses is that of starvation. Honeybees, as social organisms, depend upon external food sources. Though beekeepers can supplement their natural foods. Bees are junk food junkies. They only eat processed food. Their carbohydrate source is nectar, collected primarily from following plants, processed in the honey. Dietary needs of vitamins, mineral amino acids, cholesterol, fatty acids, etc. are supplied by pollen, collected also from plants, and processed by the bees and the bee bread for bee consumption. 

Beekeepers should evaluate the amount of stored honey and bee bread during fall manipulations. Beekeepers can feed sugar syrup or dry sugar and or pollen patties to strengthen their colony, but need to make such decisions early enough so that bees can organize their fall nest. Sufficient colony stores for successful overwintering are dependent upon the extent of beekeeper honey harvest, availability of resources during the post-peak summer, in other words, summer population phase, and rapidity of reduction in the population size, how fast the colony decreases its size to prepare and get adjusted for winter. 

Seemingly contradictory, both large colonies and smaller colonies may starve over winter. Starvation is a common reason for colony death in the spring, especially of the weaker colonies, but it may also occur in stronger colonies during spring expansion. This is brought on by all of a sudden a sudden cold snap and the colonies are always at that point living on the edge. They need large amounts of fresh pollen to expand brood rearing and nectar for their energy needs, but they have an imbalance of the worker age groups. Variable spring weather and the amount of honey and bee bread stores remaining for the previous fall are critical to colony spring expansion, as well as what they can collect as resources coming in. 

Starvation can be diagnosed by generally a total lack of stored honey in any of the cones of a dead colony. A distinct cluster formation around some calf root will likely be evident. Dead bees will be tightly packed. Brushing the dead aside will show dead bees head first in cells. That's an effort to form as tight a cluster as possible. Cap brood may be cannibalized with cell perforations with no evidence of larvae or eggs. Adults will fall into the bottom of the hive. If honey stores remain, and that is possible, it will likely be crystallized and two or more frames remote from where you see the dead cluster of bees. Right around the dead cluster, you will not see any remaining honey at all. 

Mold milk will be present often on the dead bees and in bee-bred cells. But dead cluster has been removed, diagnosis becomes a little more difficult. However, a circle of mold will persist as will dead bees headfirst inside the cells and widely scattered cat brood cells. Many perforated will still be evident. Usually this will occur in a colony that is expanding. So check weather records to determine if there was a two to four day wet cold weather event that occurred before you found the colony loss. If you do not find it right away, fly maggots or scavenger beetle larvae may be active among the dead bees, especially if there is a higher moisture level. If the colony is examined shortly after the point of plaque, some of the bees may be revived by warming them up and or feeding of sugar syrup. If frames are removed into a warmer room, some of the bees may revive. It's kind of, you know, kind of a surprise. And, you know, many of them have really been stressed. And although they might revived, they're not going to live very much longer. 

So that brings us to the viruses, which we know are spread by varroa mites. The major factor in bee colony demise is varroa mites. Heavy mite populations lead to what is labeled as PMS, parasitic mite syndrome, or often in the fall, we can diagnose it as PMS, parasitic mite brood syndrome, because the brood is going to tell us an awful lot of what is happening in those fall colonies preparing for winter.  

Fall colonies will have inadequate adult populations to cover the brood area. This may not be really evident, but You'll have a large brood area, but just the fall number of bees are just not enough to really cover it. The brood pattern, very characteristic, will be spotty. We call this snotty brood due to hygienic worker behaviors of removing cat brood, looking for mites, and formerly cap brood will be often partially cannibalized depending on the degree of hygienicity. And some larvae will be dying. This is a characteristic we term snot or cruddy brood. It's due to their unique appearance.

Some dying larvae may closely resemble the symptoms of EFB, those classic symptoms, although lab analysis often, if you do that, will not find the EFB pattern. And of course, you can have this looked at free at the Beltsville Research Station in Beltsville, Maryland, USDA station. Capped brood may have perforations and be sunken, but otherwise not have the symptoms of AFB. Lab examination does not find the AFB pathogen. Looking at the brood cells, you might note a bright white stain on the upper cell wall. This is where the mites will release their poop. So it's mite guano.

And what are mites on dying capped pupae. You may actually see mite families and cells often after you remove the bee body there at the bottom of the cell. You may or may not see dead bees or brood on the bottom board or in front of colonies. Colonies with PMS, parasitic mite syndrome, present several signs that can be confused with others. But one of the characteristics is often when we find them, it's just there's no bee bodies. Where did all the bees go? And we believe they are leaving their hive in an attempt to help preserve their society. Eventually, colonies with PMS demonstrate decreased adult bee numbers as fewer replacement bees are reared. 

 Viral diseases will cause a sudden collapse of the colony. You may look at them and think everything is okay. And all of a sudden, two to three weeks later, boy, this colony is under great stress. Something that we originally termed CCD, colony collapse disorder. We prefer the term the PMS, parasitic mite syndrome these days. And an otherwise strong colony may collapse, as I indicated, within three to four weeks, sometime during that winter period. The empty hive will have scattered brood on several frames with many of the cappings with perforations. Honey may remain, and a small cluster of bees with the may be seen. In other words, you're looking and say, maybe this is too small a population. At the time of death, yes, it is too small, but it is ultimately due to the virus. Or the colony has few dead adults scattered on frames.

 If weather has been cold at night, sometimes the remaining bees and queen abandon the brood area, their original brood area, and move to a new portion of the comb. And they seek to rear new brood in an area, apparently they're trying to get away from the mite-infested brood area. In other instances, they completely abandon, abscond their nest. Mite-controlled treatments that you may have made may be too late to rescue such highly stressed colonies, particularly if they have a virus epidemic. If the colony does not collapse, the critical mass of the diutaninous bees, those are the bees that are raised that will live longer over the winter period in the colony with the dwindling adult and mite population seek to cluster into the dormant during that dormant winter phase, but are dead by midwinter or very early in spring. We may discover them a little bit later in spring.

Mite treatment should be started early in the season after sampling to determine if mite numbers exceed 2% of the adult population. If in doubt, a diagnosis of varroa mites will likely be correct rather than too few or starvation. It can occur even with low mite numbers because it is not the mites. It's the virus that is the cause of the colony demise. 

 For those that are on the website, you will notice that we have included a photo. The photo is me examining a dead colony. I'm doing the necropsy of a colony. This colony was small in size. It was a late season colony that we had split from another one. We had attempted to feed them dry sugar over winter. The queen and the colony were alive in March and by April the next month, the colony was dead. You can see I'm looking at the cluster. Beneath the cluster is brood. They were starting their spring, but they just simply ran out of food. So this diagnosis would have been starvation.

 In conclusion, whatever the season, beekeepers are continuing to suffer extensive winter losses. Factors of bee health are complexly interrelated. An individual colony demise is likely due to multiple factors. A bee necropsy may help eliminate some possible reasons, but may not ultimately do to a single definitive diagnosis of reason for loss. Mites spreading virus disease is often the ultimate reason. I will elaborate more on mites in the next Bee-Science miniseries podcast.

 Until then, be well.