If a colony is heavily infected with Chalkbrood, then chalkbrood mummies can be found at the entrance. Photo Courtesy of Rob Snyder and the Bee Informed Partnership
Many diseases and pathogens infect honey bee colonies, but chalkbrood is likely the most common among beekeepers. Ascosphaera apis causes chalkbrood, which is a fungal brood disease. Beekeepers commonly detect chalkbrood in the spring because chalkbrood is considered a stress-related disease. However, chalkbrood is observed throughout the year. Many times, chalkbrood becomes established in colonies because of many interacting factors, such as environmental stressors, genetic makeup of colonies and beekeeping practices. Chalkbrood contaminates larvae when nurse bees admix chalkbrood spores with brood food. The fungal spores out-compete larvae for food and eventually, turn larvae into “chalk-like” mummies. Beekeepers can observe chalkbrood in many colors, ranging from white to grey to black. As larvae turn black, the chalkbrood begins producing fruiting bodies, which are highly infectious. Beekeepers can find these mummies at the entrance or bottom boards, especially if chalkbrood is widespread. At this point these mummies can spread spores to other colonies in the area. Chalkbrood often infects 3-4 day larvae, and can be found as uncapped or capped larvae. If the colony shakes a frame with capped chalkbrood, the frame will rattle when shaken.
Black chalkbrood mummies with fruiting bodies, which are highly infectious. Photo Courtesy of Rob Snyder and the Bee Informed Partnership
Symptoms
Spotty brood pattern
Chalk-like (white, grey or black) mummies at the colony entrance, chalk-like mummies in open brood.
Early stages of Chalkbrood look very similar to Sacbrood Virus. However, the larval head is less defined with a sunken appearance.
Chalkbrood mummies. Photo Courtesy of Rob Snyder and the Bee Informed Partnership
Sacbrood virus, which has a distinct look to Chalkbrood, even though they share similarities. Photo Courtesy of Rob Snyder and the Bee Informed Partnership
3 Major factors why Colonies have colonies get chalkbrood
Environmental StressorsChalkbrood outbreaks increase when colonies have a lessened ability to care for brood or maintain the optimal brood temperature of 35°. Remember: Chalkbrood is a stress-related disease, so cold and wet temperatures can proliferate the fungal disease. The following are environmental stressors the may induce Chalkbrood outbreaks:
Brood chilling
When it is cold and wet during spring population increase. Chalkbrood often occurs during rapid growth periods and when the colony has a higher brood:worker ratio.
Reduced foraging and habitat due to agriculture intensification. Agrochemicals can immunocompromised adult honey bees, which may weaken the honey bees ability to care for brood. Agrochemicals include both agriculture sprayed chemicals and beekeeping miticides.
2. Genetics
Honey bees have significant genetic variation between strains. For example, certain honey bee strains are more resistant to chalkbrood. Because of this, selective breeding for chalkbrood resistance is possible. A great example is hygienic behavior, which have known resistance to chalkbrood.
3. Stressors from other pests, pathogens and diseases
Chalkbrood is a stress-related fungal disease, and a contemporary honey bee stressor is other pest, pathogens, and diseases. Honey bees can be co-infected with other pests (varroa mites), viral infections (Deformed Winged Virus) and pathogens (American and European Foulbrood), which are stressors that can induced a Chalkbrood outbreak. Below are examples where the co-infection of other pests and pathogens can induce a Chalkbrood outbreak:
Chalkbrood is associated with Deformed Wing Virus, a common virus associated with varroa.
Chalkbrood outbreaks is correlated to both Varroa destructor and Nosema ceranae.
A mixture of white, grey and black chalkbrood mummies within a heavily infected colony. Photo Courtesy of Rob Snyder and the Bee Informed Partnership
Factors that affect the spread of Chalkbrood
Virulence
Chalkbrood virulence (the severity of harmfulness of the disease) is dependent upon the strain. A more virulent strain of chalkbrood will spread and kill a colonies more quickly. Remember: not all chalkbrood is the same and some strains are more virulent than others.
Social Immunity
Colonies bred for hygienic behavior have a reduced prevalence of chalkbrood. But, remember, hygienic behavior is most effective during early detection of chalkbrood, which means the early detection of larval death. If chalkbrood is detected during the late stage and potentially sporulation chalkbrood mummies are removed, hygienic behavior could increase rather than decrease transmission of chalkbrood spores.
Beekeeping Practices
Management and sanitation practices should aim to reduce transmission
Keep equipment clean to avoid transfer of chalkbrood among colonies
Either removed old comb from your operation or avoid the transfer of contaminated comb among colonies.
Reduce Stressors
Reduce environmental stressors, such as low forage, nutritional limitation, and agrochemical exposure
Reduce co-infections with other pest, pathogens and diseases.
Breed bees for hygienic behavior or select bees for chalkbrood resistance
3-4 day old larvae infected with Chalkbrood, a common fungal disease. Photo Courtesy of Rob Snyder and the Bee Informed Partnership.
Prevention
Increase ventilation and airflow into colony
Replace and removed old comb. Old comb contains spores and is often the source of a chalkbrood outbreak. Be cautious when buying old equipment and comb.
Re-queen colonies with queens bred for hygienic behavior
Maintain strong colonies
Treatment
Thymol based treatments are thought to effectively treat chalkbrood. But this is purely anecdotal. Thymol based treatments include apiguard, Vitafeed Green and beevital are commonly used, and many beekeepers believe they are effective. While these thymol based treatments may work, I have not seen it.
Varroa infested colonies entered the United States in ~1987, and changed beekeeping forever. Beekeeping has always been time consuming, difficult and experience oriented; however, beekeeping became even more challenging when beekeepers were called to eradicate a bug on another bug. Since its introduction in the US, beekeepers have reported high annual colony losses due to mites. In fact, some beekeepers report 60% losses due to this troublesome pest. While beekeepers have faced devastating challenges before, including American Foulbrood, Varroa mites has presented damages never before seen.
Varroa have become more difficult to manage since their introduction. The mites are seemingly embedded within the honey bee industry reality as nearly, if not all, colonies have Varroa. Like many beekeepers say: ” all my colonies have mites, I just cannot see them”. Even if alcohol washes do not reveal mites, Varroa is present in the brood or will be present soon due to infestation from surrounding colonies. As mites have become more widespread, they became a vector for a variety of viruses. In fact, researchers are finding more and more variants of Deformed Wing Virus (DWV), a virus that affects the honey bee’s essential flight capabilities. Research has shown that DWV-B (Deformed Wing Virus variant B) can be responsible for high over-winter losses.
The point here is that Varroa devastates colonies. It would also seem that Varroa are transmitting more virulent strains of viruses with each passing year. Because of this, I recommend to keep mite levels below 1 mite/ 100 bees in the spring and below 3 mites/100 bees in the fall. With Varroa loads any higher, beekeepers risk high colony losses.
Monitor, Monitor, Monitor
Beekeepers must consistently monitor mites if they expect to have strong and healthy colonies. Beekeepers can monitor their mites in various ways, but I recommend both of these two methods: perform an alcohol wash (or other monitoring method) and observe the overt signs of mite damage. It is ideal to perform monitoring methods once a month, but we realize this is not always possible. Because of this, combining both monitoring and observation methods are recommended. Ideally, mites should be monitored at least 4 times a year. As seen in Figure 1: population increase, population peak, population decrease, and fall dormant; it is essential to understand the seasonal changes. For example, brood density varies throughout the year, so certain treatments can be less effective at different times. By understanding seasonal cycles, beekeepers can better manage their mites. I understand Figure 1 does not reflect the reality of every region but it gives a good overall general idea. Some regions have multiple population peaks due to large honey flows, so you will need to understand the honey bee seasonal phases in your region. But essentially, as the bee and brood population increase, so do the mites.
Figure 1: Honey bee seasonal phases from the honey bee health coalition- Beekeepers should monitor mites once a month, but this is often not possible. But mites should be monitored at least 4 times a year: late winter-early spring dormant, population increase, population peak, population decrease, and fall dormant. I recommend alcohol washes (or another method) during these periods. Photo courtesy of the Honey Bee Health Coalition
Mite Monitoring Techniques
I attached a chart outlining the 3 major mite monitoring techniques I recommend. Perform one of these techniques 4 times a year: Early spring, late spring, late summer and early fall. Each beekeeper has their preference, so use the method you feel the most comfortable with. I use alcohol washes, but I feel comfortable with sugar rolls or CO2 as well. As long as you monitor, there is not a wrong method!
Advantages
Disadvantages
Sugar Rolls
Known research on accuracy
Common method
Does not kill bees
Messy
Hard to do on windy, rainy or humid days
More time consuming
Alcohol Wash
Known and common method
Quicker than sugar rolls
Can be more accurate than sugar roll
Can be messy
Kills bees
CO2
Quickest method
Easy to do with multiple colonies
Kills the bees (most likely)
When monitoring for mites, beekeepers should review mite thresholds. I outline my recommended thresholds for each monitoring method below. If your colony is above threshold, I recommend taking actions. Mite thresholds are not an exact science, even if you have levels below the threshold, it is no assurance that your colonies will be healthy and successful. For example, I have sampled many commercial beekeepers with mite levels <0.5 mites /100 bees in the spring, and they eventually had huge losses. I typically see mite levels spike in the late summer because: A) summer treatment with honey supers are limited, B) Mites are often lurking in the brood, and C) Mites from other beekeepers nearby can (re)infest colonies. Because of this, always monitor and monitor again. Once mite levels do spike, they may be difficult to bring down. Too often, when you notice, the mite damage is already done. I should note that I recommend alcohol washes, powdered sugar rolls or CO2 over a sticky board. Sticky boards are not nearly as accurate, because they do not quantify the level of infestation. If a sticky board is your only option, you can attest that you have some mites or more mites, but you are not able to assess the level of infestation (1, 2, 3 mites/100 bees). Use other monitoring method options for more accurate results and an infestation level to compare with suggested thresholds. *These thresholds may vary per US regions. These are the threshold I recommend in the Midwest (MN & ND)
Monitoring Method
# of mites in early-spring
# of mites in mid-spring
# of mites in late-spring
# of mites in early-fall
# of mites in late-fall
Alcohol Wash
1 mite/100 bees
1 mite/100 bees
1 mite/100 bees
3 mite/100 bees
3 mite/100 bees
Powdered sugar roll
1 mite/100 bees
1 mite/100 bees
1 mite/100 bees
3 mite/100 bees
3 mite/100 bees
CO2
1 mite/100 bees
1 mite/100 bees
1 mite/100 bees
3 mite/100 bees
3 mite/100 bees
Sticky Board
9 mites/24 hours
9 mites/24 hours
9 mites/24 hours
12 mites/24 hours
12 mites/24 hours
Mite related Disease Progression
I inspect and observe hundreds of colonies annually. When I enter a colony, I often immediately know whether it has (or did) have high mite levels simply by observing progressed signs of mite damage. Just observing progressed mite damage does not suffice, but it is a good start. By noting visual signs of Varroa, you will know just how important your mite levels are and the need for action. Monitoring is best but if you can recognize some of the visual signs, you will better understand the extend of the mite damage to your colony.
I outlined the 5 stages of mite damage, which I relay to my beekeepers. In the spring during population increase, I want to see colonies within the Stage 1- 2. While I hate to see mites in the spring, this is not always a bad sign. Even if I observe mites, the colony may be below the recommended threshold, so just continue to monitor that colony. During the late spring, summer and fall, I like to see colonies within Stage 1-3. Even if Chewed Down brood (CDB) (outlined below) and phoretic mites are seen, it does not mean that beekeepers have high levels. However, a combination of phoretic mites and CDB can signal worse mite issues. If these signs are seen, continue to monitor these colonies. As for Stage 4-5, I never want to see these stages, regardless of temporal period. Deformed Wing Virus (DWV) and Varroa Mite Syndrome (formerly Parasitic Mite Syndrome or PMS) can signify high mite levels. Specifically for Varroa Mite Syndrome, it signifies very progressed mite damage, which often results in colony deterioration and eventual colony death. If colonies are in stage 4 or stage 5, monitor immediately to determine extent of damage. Action is often required, but may be too late.
Stage
Visual Signs
Notes
Stage 1
Zero signs of mites, brood diseases or viruses
Stage 2
Visual signs of phoretic mites on either workers or drones.
This does not necessarily mean a mite issue exists, but if mites are seen, monitor to determine extent of varroosis.
Stage 3
Chewed Down Brood and/or phoretic mites
Stage 4
Deformed Wing Virus (DWV) and/or Chewed Down Brood and/or signs of phoretic mites.
Visual signs of Deformed Wing Virus (DWV) can mean larger varroa issues. Obviously, this depends upon the number of bees with DWV and the number of phoretic mites seen, but mite monitoring is recommended to determined extent of varroosis. These signs signal a more progressed form of varroosis.
Visual signs of Parasitic Mite Syndrome usually signal extreme issues with varroosis. If Parasistic Mite Syndrome is seen, then mite levels are often a significant issue and has advanced to the most progressed stage of varroosis.
Visual signs
Phoretic Mite
Phoretic mites are Varroa mites seen on the abdomen of worker (or drone bees). Most phoretic mites, however, are found underneath the bee, more precisely tucked between the abdomen’s sclerites where they latch on and feed. Because of this, I typically inspect the ventral abdomen of several worker bees during inspections. This is why beekeepers “never see mites”, even if these beekeepers have higher mite levels. Visually inspect phoretic mites just on the workers, not the drones. If phoretic mites are seen on worker bees, then this represents a more progressed infestation of mites. Signs of phoretic mites indicate the colony is in Stage 2-5. Visually inspect other signs to further pinpoint extent of damage.
Phoretic mite on the thorax of a worker bee. Photo Courtesy of Rob Snyder
Chewed Down Brood (CDB)
Bees can sense mites in the brood. If sensed, bees will uncap and cannibalize the pupae. If CDB is seen, then mites may be at a high level, especially within the brood. CDB can indicate progressed mite damage, so continue to monitor and assess colony health.
Deformed Wing Virus (DWV)
Deformed Wing Virus (DWV) represents the next stage of varroosis progression. Bees with DWV are kicked out of the colony so if bees with DWV are seen than Varroa has become an issue. DWV does not signify un-manageable mite levels for the colony, but it is a more progressed sign of mite damage.
The bottom right corner contains a cell with chewed brood. Bees begin chewing brood when they sense mites within the cell, so this can indicate larger mite issues. Photo by Rob Snyder
Deformed Wing Virus (DWV)
Deformed Wing Virus represents the next stage of varroosis progression. Bees with Deformed Wing Virus are kicked out of the colony so if bees with DWV are seen than Varroa has become an issue. Deformed Wing Virus does not signify un-manageable mite levels for the colony, but it is a more progressed sign of mite damage.
This bee has deformed wing virus, a debilitating virus than can easily deplete a colony. Oftentimes, bees with the virus are removed from the colony. So if bees with Deformed Wing Virus are seen, than this can indicate larger issues. Photo by Rob Snyder
Varroa Mite Syndrome (VMS)
A pathogen has not been identified for this diseased, however mites are always present when this disease is seen. This brood symptom looks similar to other brood diseases except the larvae do not rope like foulbrood. Larvae do appear sunken to the side of the cell. If Varroa Mite Syndrome is observed, then colony has likely dwindled and deteriorated. Varroa Mite Syndrome is the most progressed sign of mite damage, and truly at a stage of no return. Even if low phoretic mites are seen, Varroa mite syndrome often means an end to your colony, even if treatment is applied.
Symptoms
Spotty brood and Varroa present on adult
Mites may be present on brood
Mites seen on open brood cells
Small population size
No odor present, just sunken brood
Parasitic mite syndrome is the most progressed sign of mite damage. If parasitic mite syndrome is seen, than the damage is done. These colonies will likely collapse, and there is nothing a beekeeper can really do. At this stage, the colony has already dwindled and deteriorated.
Summary
All beekeepers should consistently monitor mites throughout the year. Even if mite levels are low at one point, it does not mean they will stay low. Mite levels can easily spike, so always be aware and monitor and re-monitor. Beekeepers should learn how to monitor and visually inspect for mites. By doing so, varroa mites can effectively be managed. Varroa mites are the most challenging issue beekeepers face, so make sure you know where your colonies stand. If you don’t, then you risk losing your colonies.
Garett Slater 