Deciding when to treat for varroa mites is important for both commercial beekeepers and hobbyists. Beekeepers shoulder the responsibility of finding the balance between proactive pest management and avoiding excessive interference with colony dynamics. This article serves as a guide for beekeepers grappling with the choice of when to initiate treatment.
Importance of Varroa Mite Management in Time
Varroa mites feed on honey bees' fat bodies, making the colonies weak and unproductive. These mites also act as carriers for viruses and diseases.
The consequences of allowing varroa mite populations to escalate are severe, resulting in significant colony losses. Stressed colonies result from high mite numbers. These colonies become more vulnerable to issues such as European Foulbrood and Nosema disease. This underscores the crucial importance of varroa mite management in time.
Thresholds for Treating Bee Mites
To control varroa mites, there are numerous approved treatments available. However, it's essential to recognize that any treatment plan, including natural approaches, induces stress on our colonies. To avoid unnecessary interventions and alleviate the financial burden on beekeepers with large apiaries, researchers have introduced treatment thresholds.
Beekeepers use these thresholds as general guidelines to decide when to intervene against varroa mites. Research often refers to one key threshold as the "economic threshold." It signifies a point where mite infestation reaches a critical level, leading to colony decline and reduced productivity. Allowing mite numbers to persist can ultimately result in colony death.
We have to note that these threshold numbers are somewhat flexible. They vary between regions, experts, and even from year to year. While they provide valuable guidance, consider them as guidelines rather than rigid rules.
Over the years, acceptable mite levels have steadily decreased. We've learned that even fewer mites than previously believed can harm bees significantly.
The treatment schedule for mites is not a one-size-fits-all calendar. When to treat honey bee colonies for mites depends on factors such as your bees' genetics, the chosen mite control product, and your location. Different honey bee populations show varying sensitivities to mite problems. Certain regions may face more significant challenges with mites.
Therefore, beekeepers must acquire the skills to monitor mite levels within their hives. Based on these observations, people can make informed decisions on whether and when to take corrective action.
Monitoring for Mite Levels:
New beekeepers often say they can directly see mites on adult bees. However, such visual checks are insufficient for gauging infestation levels. The majority of mites reproducing in brood cells remain invisible during visual inspections. By the time mites are noticeable in adult bees, it might be too late to save the colony.
To accurately assess varroa mite levels, beekeepers commonly employ methods like the alcohol roll and sugar shake. The less accurate method is the bottom board drop count.
Once you determine the estimated mite levels, it's crucial to analyze the findings. The general guideline suggests applying treatment if the infestation exceeds 2%. However, the time of year also plays a significant role. Suggestions usually propose treatment if the infestation exceeds 1% in the spring and 3% in the autumn.
We can assess the mite infestation rate with a sample of 300 bees. We can approximately get 300 bees from the brood box with a standard half-cup measure. For instance, if we find 9 varroa mites in these sample bee colonies, the result suggests a 3% infestation rate (9 mites /300 bees). In such a case, treatment for varroa mites is necessary.
What actions should we take if the mite infestation level is at 2% or a little higher than 1%? Can a single mite test provide accurate results? While some beekeepers advocate for multiple counts for precision, not everyone follows this practice.
The decision to treat bees for mites with infestation levels below 3% depends on various factors. In areas where beekeepers recognize mites as a common issue, they often need to administer treatment. Discovering no mites or a 1% level might lead you to observe and wait for a while, but it comes with risks.
If the infestation level reaches 2% or higher, beekeepers face a decision based on their schedule, and the time of year. They may proceed with a treatment to maintain a low mite population.
Late Season Varroa Mite Explosions:
Why do numerous beekeepers witness low mite levels only to encounter dead beehives by late autumn? The substantial, thriving colonies appear to diminish or vanish rapidly. To comprehend this phenomenon, let's explore the life cycle of honeybees and Varroa mites.
Honeybees Life Cycle:
The life cycle of honeybees unfolds differently than that of varroa mites. Worker bees develop from an egg to a fully grown adult in 21 days; Queens take 16 days, and drone bees require 24 days. Notably, the colony's total population and the ratio of workers to drones fluctuate all year.
Life Cycle of Varroa Mite:
- Phoretic Stage:
Varroa mites, in their phoretic stage, ride on adult bees for 5-11 days, with this period extending through winter in the absence of brood. This mated female, known as the foundress mite, clings to adult bees, preparing for the next reproductive phase.
- Reproductive Phase:
During the reproductive phase, foundress mites enter brood cells housing developing larvae. Inside these cells, reproduction takes place exclusively.
The process involves the foundress mite producing a male mite initially, followed by daughters. The mite's complex way of reproducing only occurs inside brood cells. This ensures that the mite's life cycle aligns with the growth of honey bee larvae.
- Treatment Challenges:
Treatment of varroa mites presents challenges because of the specific targeting of phoretic mites in many existing treatments. Unfortunately, these treatments may overlook mites concealed within brood cells.
To effectively address varroa mites, a comprehensive approach is essential. Beekeepers have to consider the presence of mites both outside and inside the brood cells. This detailed strategy applies to the different stages of the mite's life cycle.
Varroa Mite Reproduction in Worker Bee Cells:
In the worker bee brood, a varroa mite inside a capped cell has about 11 days to produce about 1.5 female mites on average. The new mite mates with her brother. They feed on the growing bees， which may weaken the bees and spread illness.
Upon the emergence of the new bee (if it survives), the mother mite and her mated daughter also emerge. The male mite dies inside the worker brood cell. Thus, the original 1 mite that entered the cell results in 2 emerging after about 11 days.
These two fertile female mites then enter a new brood cell, each producing a viable daughter. Although the original mother mite nears the end of her life, three females, including the foundress mite, remain inside the hive.
The population of varroa mites increases three times each month through reproduction in worker bee cells.
Effect of Drone Brood on Mite Reproduction:
Drone brood, which has a lengthier 24-day cycle, significantly impacts the Varroa mite population. Varroa mites can detect the type of brood cell by sensing the odor of bee pheromones.
Typically, a drone cell produces a mother mite and two viable daughters, resulting in three mites instead of two. These three mites then move to another drone cell. After 14 days, eight viable mites emerge as the mother mite reaches the end of her life span.
In approximately a month (36-38 days), a single foundress mite increases its population to eight. This rapid reproduction can intensify with hundreds of mites in numerous drone brood cells.
Uncontrolled Varroa Mite Reproduction:
The uncontrolled reproductive growth of Varroa mites in a beehive can lead to a significant increase in population. When relying on worker brood alone, the mite population grows three times bigger within a month. However, the presence of drone brood can cause the population to double every two weeks.
Research reveals that for each phoretic mite found on a bee, there are 2-3 additional mites concealed under the brood cappings. For instance, discovering 100 mites on house bees in July implies about 300 more hidden under the caps. This results in a total of 400 mites.
The monthly progression reveals an exponential increase: 400 mites (July), 1200 mites (August), and 2400 mites (September). Note that these calculations focus on mite reproduction in worker brood cells. We have not to mention the potentially higher rates in drone brood.
Autumn Absconds or Intense Mite Infestations?
Late summer or autumn absconds, often called "absconding beehives," are not rare. This term describes situations where all the bees leave the hive. This is different from regular bee swarming that some bees stay in the hive. In an absconding event, few or no bees remain in the hive.
Some of these empty autumn hives might not be real absconding incidents. Instead, they could be colonies collapsing because of overwhelming varroa mite loads.
The reasons for this are unclear. It may be because bees are trying to escape a worsening situation. Too many varroa mites cause this situation.
Optimal Times for Varroa Mite Treatment:
Determining precisely when to treat bees for varroa mites can be challenging. However, we can offer some general guidelines to beekeepers. You should consider an early Spring treatment in many cases and include it in your routine Spring beekeeping tasks.
This early intervention helps reduce mite loads before nectar flow starts. Note that you can not apply most of mite control treatments when honey supers are present. So, make sure to read product labels carefully.
Continuous monitoring of mite levels throughout the season is essential. By mid-July, numerous colonies experience a decline in egg laying, with older bees outnumbering emerging ones. While the population is dropping, mite numbers persistently triple each month.
When varroa mite populations increase, the numbers of bee brood cells decrease. We reach a crucial point that almost every brood cell contains a mite. If not addressed earlier, a late summer mite treatment becomes necessary. It helps reduce mite numbers and enables the colony to rear robust fat bees for winter.
Avoid waiting until autumn, as it might be too late. Whether employing oxalic acid vaporization, formic acid, fluvalinate strips or alternative methods, take action if required. Subsequently, assess the effectiveness of the chosen treatment to ensure its success.
Non-Treatment Approach —— Mite-Resistant Bees:
Numerous beekeepers seek alternatives to chemical treatments. They look forward to a promising future with the breeding efforts dedicated to developing mite-resistant bees. However, the harsh truth is that most beekeepers face the risk of a severe mite crash. This leads to the death of bee colonies if they do not take any effective mite control steps.
Despite the appealing idea of not worrying about varroa mites, the reality is often harsh. This results in the unnecessary loss of beehives for many.
Closing Remarks:
The prospect of mite-resistant bee breeding holds promise for the future. Though I haven't discovered a bee that can thrive without treatment in my region, I maintain optimism. Regularly check mite counts, and stay tuned about the latest recommendations for addressing varroa issues. These guidelines may change over time.
Remember, the right time to treat bees for varroa mites is before it's too late. The stark reality is that once your hive crosses a certain threshold, recovery becomes an overwhelming challenge.
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