When to Cull a Colony

When to Cull a Colony

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The good news is culling is usually not necessary. Read on to discover when to cull a diseased colony and when to try other methods first. 

Beekeeping is tough work. It’s hard on the back, hard in the heat, and the stings don’t feel too great, either. Yet, every single day, beekeepers across the globe continue to gather their tools and head to the bee yard to see what the bees are up to. The hope is the colonies will look outstanding, be producing loads of luscious honey, and everything will be running as smoothly as a fairy tale. However, there will be times when hard decisions must be made for the sake of the apiary’s continued well being. One such time is when disease strikes. The good news is, culling is usually not necessary as most diseases are readily managed with only a few instances to the contrary. Read on to discover when to cull a diseased colony and when to try other methods first.  

Tracheal Mites  

Tracheal mites (Acarapis woodi) are mites that infest and then breed inside the honey bee’s breathing passages, causing a reduction in the bee’s breathing ability as well as vectoring disease. While not a serious issue in many areas nowadays, tracheal mites are still a very real threat in some regions and need to be addressed promptly if the colony is to survive. However, culling is not typically necessary as steps are easily taken to remedy the situation.   

We all hope and strive for a perfectly healthy colony during our inspections. Sadly, not every day’s inspection can be this perfect.  

Honey bees plagued by tracheal mites typically exhibit k-wing, a condition in which the bee’s wings do not lay flat against the back, but rather one wing sticks out even at rest, giving the wings a ‘k’ shape. However, k-wing is present in many diseases and is not a certain indicator of tracheal mite infestations. In addition to k-wing, infested bees will also be seen wandering listlessly around the ground and the landing board, obviously struggling to get around.   

Diagnosis can only be confirmed under a microscope. Rather than cull the colony, however, treatments such as Mite-a-Thol, Mite-Away-II, Apilife Var, and Apiguard are effective alternatives and can save the colony with little effort.   


One disease we often see in spring during the cold, wet weather and which is exhibited by streaks of brown fecal matter across the fronts of hives and on the inside hive walls in extreme cases is nosema (Nosema apis, N. ceranae). Caused by a protozoan living in the gut of the honey bee, nosema causes symptoms such as diarrhea (dysentery) and distended abdomens. Stressed colonies struggle to maintain hive cleanliness and production is stymied. However, yet again, no need to cull the colony just yet as Fumadil-B is an effective treatment when needed.  

Wax moths are another pest that destroys colonies, but they usually only attack weak colonies that are incapable of fending off the moths. Again, these are pests and not disease, making culling unnecessary but rather intervention.  

Sac brood  

Caused by a virus, sac brood occurs most often in weakened colonies and presents with dead, watery larvae exhibiting a thickish skin. Larvae are seen in a canoe shape with the head poking towards the top of the cell. This disease also scares many folks, but the good news is that while there is no chemical treatment for sac brood, the simple act of requeening with new stock is most often all that is needed to break the cycle of sac brood instead of culling. Prevention is best accomplished via the maintenance of strong colonies.  


It is not uncommon after a cold spell to notice dried up, mummified bee larvae littering the landing board and the ground just in front of the colony as house bees remove larvae killed by the cold. Caused by the fungus Ascophera apis, chalkbrood is much like the aforementioned scenarios—culling is not needed for the disease. Rather, if cold weather is nearly over, many colonies overcome the chalkbrood on their own. However, in extreme cases, it is recommended to requeen with hygienic and/or resistance stock. Preventive measures are just like they are for other diseases — the maintenance of strong colonies is often all that is needed to keep this disease at bay.  

Pest infestations such these small hive beetle larvae, while they can certainly destroy a colony through their actions, are not a cause for culling. Other management practices will strengthen colony numbers while reducing SHB populations are in order.   

European Foulbrood  

Just say the word foulbrood in any beekeeping group and you may hear shudders echo throughout the room. Foulbrood is the dread of all beekeepers and is known as the one surefire way to lose a colony. However, European Foulbrood (EFB) is not the foul brood that requires the colony’s destruction.  

EFB is caused by the bacterium Melissococcus pluton. This bacteria causes brood to turn a dull white at first with colors changing to brown and black. Most often the deceased larvae will be younger larvae that is uncapped, making visualization easier. When larvae are manipulated with a toothpick, the larvae is discovered to be rubbery and not stretchy like elastic as seen in American Foulbrood.  

Treatment for EFB is also simple with a prescription of Terramycin from your local veterinarian and not the destruction of the colony as so many fear. Just like most diseases, maintaining a strong colony is one of the most successful steps for preventing this particular form of foulbrood.  

American Foulbrood  

American foul brood, caused by the spore-forming bacterium Paenibacillus, is the disease everyone fears most. This form of foul-brood is the disease that most states require complete destruction of the colony including all boxes, all top and bottom boards, all frames and foundation including brood and wax as well as all honey bees within the affected colony. Once burned, all remains most often must be buried in the ground to prevent further spread. Most often, all apiaries within the area are notified by the State Honey Bee Inspector of the AFB outbreak and remaining apiaries are often placed in quarantine. The seriousness of AFB may require complete apiary destruction if not caught early enough.    

Seriously spotty brood is one inspection discovery that sends many new beekeepers running to their mentor for advice. However, spotty brood doesn’t always mean disease and it nearly never indicates the need for culling, but rather a need for further inspection.  

State inspectors are the best source of confirmation should you suspect this vile disease has entered your operation. However, symptoms are readily visible with ropey, stretchy deceased larvae being the number one indicator for the lay person. This ropiness may be observed by placing a toothpick inside the affected cell and stirring the remaining larvae a bit before pulling the toothpick from the cell. In AFB, the larvae tends to stick to the toothpick and stretch like elastic. When AFB is suspected, it is always best to contact your state inspector for guidance. There is currently no approved cure for AFB except for the complete destruction of the colony. This is the only situation where culling is a for sure bet in most states and in most situations.  

Knowing when to cull a diseased colony can be a bit distressing, particularly when you’ve never seen disease before. The good news, however, is most diseased colonies are just like any other diseased livestock. Most cases are easily prevented with most diseases being a fairly simple matter of administering a medication and/or requeening with resistant or hygienic stock. This approach is much simpler and much less destructive than culling a savable colony. So before you decide to cull for disease, be sure to verify the need beforehand. There will always be other times to cull. Just not for disease in most cases.  

Originally published in the Fall 2022 issue of Backyard Beekeeping and regularly vetted for accuracy.

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