Varroa Destructor: How To Kill Varroa Mites
- Laurence Edwards
- Nov 10, 2024
- 5 min read
Understanding the Varroa Mite Lifecycle
As beekeepers, we know all too well that the Varroa destructor mite is the honeybee's worst enemy. These tiny parasites can wreak havoc on our hives if left unchecked, leading to the collapse of colonies within just 2-3 years. However, the key to effectively managing Varroa is understanding its complex lifecycle and reproductive cycle.
The Varroa mite is a formidable foe, measuring just 1-1.8 mm in size. While seemingly insignificant compared to the honeybee, the Varroa mite is akin to a rabbit latching onto a human's shoulder or belly. Bees have limited natural defences against these hardy pests, and the real danger lies in the viruses they transmit rather than the physical damage they cause.
Learn more about the varroa mite HERE - https://en.wikipedia.org/wiki/Varroa_destructor
The Varroa mite's lifecycle is perfectly synchronized with that of the honeybee, making it a highly successful invasive species. Female Varroa mites will enter the brood cells, typically targeting drone brood, and lay their eggs. The first egg laid is a male, often followed by several female eggs. The male mites emerge first, before the honeybee, and mate with the female mites within the cell. By the time the honeybee emerges, the female mites are already fertilised and ready to continue the cycle.
This rapid reproduction rate is what makes Varroa so difficult to control. A single female mite can produce up to 3-4 offspring in a single brood cell, and those offspring will be ready to repeat the process in just 7-8 days. As the colony produces more brood throughout the summer, the Varroa population can explode exponentially, quickly overwhelming the bees' defences.
The Varroa Threat: A Seasonal Ebb and Flow
The Varroa threat ebbs and flows throughout the beekeeping season, with a critical period occurring in the late summer and early autumn. During the height of the summer, the large bee population is able to somewhat keep the Varroa numbers in check. However, as the days start to shorten after the summer solstice, the queen begins to reduce brood production. This creates a mismatch, where the Varroa population continues to grow while the bee population declines, leading to a dangerous Varroa-to-bee ratio.
This late summer/early autumn period is a crucial time for Varroa management. As the number of bees in the colony reduces, the tolerable mite population can quickly spiral out of control if left unchecked. Beekeepers must act decisively to bring Varroa numbers down before the winter bees are produced, as the damage is already done if Varroa is allowed to proliferate unchecked.
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Timing is Everything: Varroa Treatment Strategies
Effective Varroa management requires a two-pronged approach, with treatments timed to coincide with the mite's reproductive cycle. The first critical step is the late summer/early autumn treatment, which should be carried out around mid-August in the UK.
At this time, I recommend using an amitraz-based product, such as ApiVar, for an 8-week treatment cycle. This allows you to knock down the Varroa population before the winter bees are produced, ensuring a healthy colony heading into the colder months. It's important to note that trying to treat the winter bees is too late - the damage will already have been done. You need to treat the colony before the winter bees are produced.
The second treatment should be timed for the broodless period, typically between mid-November and early December in the UK. This is the optimal window to use oxalic acid sublimation, which can achieve a 95% knockdown of the remaining phoretic (non-reproducing) mites. By targeting the mites when there is no brood present, you can effectively eliminate the Varroa population without risking harm to the developing bees.
If the bees aren't broodless during this period, multiple blasts of oxalic acid should be used at 5 day intervals, as this is the most destructive spacing interval for the varroa mites.
Putting the Plan into Action
Implementing this two-part Varroa management strategy requires careful planning and execution. Let's walk through the steps:
Late Summer/Early Autumn Treatment
Time the treatment for mid-August, or no later than the end of August.
Remove any remaining honey supers from the hive.
Treat the bees with an amitraz-based product, such as ApiVar, following the manufacturer's instructions for an 8-week treatment cycle.
This treatment should coincide with the period when the queen is reducing brood production, ensuring the mites have fewer cells to reproduce in.
You can feed bees during Apivar treatment and also change queens if you need to.
Broodless Period Treatment
Monitor the colony closely in late November and early December and ESTIMATE a broodless period.
During this broodless window, use oxalic acid sublimation to target the remaining phoretic mites. You can also use an Oxalic Acid trickle if you don't have sublimation equipment.
Oxalic acid is highly effective at this time, as there is no brood to protect the mites from the treatment.
A single application of oxalic acid sublimation can achieve a 95% knockdown of the Varroa population.
It's important to note that I don't recommend going through your colonies to check for broodlessness yourself. As a YouTube beekeeper, I'm happy to do this and share the results, but it's generally not necessary for most beekeepers to take on this task. Instead, focus on the timing - between mid-November and early December is typically the best window to find a broodless period in the UK. You risk killing the queen and if you do, varroa treatments become superfluous as the colony will die over winter without the queen!
Staying Ahead of the Curve
Effective Varroa management is not a one-time event; it's an ongoing process that requires vigilance and a proactive approach. By understanding the Varroa lifecycle and implementing a strategic treatment plan, you can stay ahead of the varroa mites and ensure the long-term health and productivity of your colonies.
Remember, prevention is key. Maintaining low Varroa levels throughout the year is crucial, as allowing the mite population to spiral out of control can have devastating consequences. By following the two-part treatment strategy outlined above, you'll be well on your way to keeping your bees healthy and thriving.
Supporting Your Beekeeping
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Remember, by staying informed and taking proactive steps to manage Varroa, you can ensure the long-term health and success of your beekeeping endeavours. Let's work together to keep the Varroa mite at bay and enjoy the sweet rewards of a thriving, vibrant hive.
