When Should I Treat Bees for Mites
Knowing when to treat bees for varroa mites is one of the most important decisions in beekeeping. This small, reddish mite is about the size of a pencil mark. It is one of the most serious pests of honey bees. Responsible for the deaths of millions of hives each year, controlling the levels of varroa mites in your hives is key to beekeeping success.
We can only imagine how wonderful beekeeping must have been before varroa mites arrived in the United States. Alas, the immediate future (at least) in beekeeping will involve finding ways to deal with this pest.
Controlling Varroa Mites in Beehives
When do you need to worry about varroa mites? For most beekeepers, it is a necessity to treat bees for varroa mites several times a year.
The exact timing of mite treatments and how many needed will depend on the genetics of your bees, product used for mite control and where you live.
In some regions of the country, controlling varroa mites in bees is a bigger deal than others. Some parts of the country simply have a bigger problem with varroa mites than others.
Also, some strains “genetics” of honey bees are more susceptible to mite infestations. If you are involved in keeping bees and maintaining hives, you will be involved with mites too.
Doing nothing is not an option. At the very least – you must monitor mite infestations in the hive. From there, you can decide what if any action to take.
Natural Varroa Mite Control
Many beekeepers strive to move away from the use of chemical varroa mite treatments. We yearn for a more natural way to control varroa mites.
The future looks promising as bee breeders work to breed mite resistant bees. Progress is being made in bee breeding but the vast majority of beekeepers will have to use current treatment measures.
For most of us, failure to control varroa mites in the hive will result in a mite crash. This means that the bee colony dies as a result of mite infestation.
In spite of several treatment methods approved to manage the level of varroa mites in a bee colony, none are 100% reliable. And, they can have possible negative effects for the colony.
All beekeepers dislike adding chemicals to our hives. But, the desire to avoid treatments in hives with low mite numbers may be a big mistake that leads to a late season mite explosions.
Fall Absconds or Varroa Mite Bomb?
It is not uncommon to hear of late Summer or Fall absconds . An “abscond” is the term used when all the bees in the hive are gone.
They are simply gone suddenly. This differs from a swarm of bees where some of the colony remains to carry on life in the hive.
Swarming is a natural process in healthy hives. Reproductive swarms leave part of the bee population behind. In absconding, none or very few bees remain in the hive.
Perhaps some of these empty Fall hives are not true absconds but colonies collapsing from large numbers of varroa mites.
Varroa Mite Treatment Thresholds
No one wants to use mite treatments unless necessary. Any treatment plan (even natural ones) causes some stress to our honey bee colonies.
And, beekeepers with a lot of hives may find it expensive to treat their hives. Bee researchers have developed treatment thresholds to help beekeepers decide when treatment is needed.
Economic Threshold for Varroa Mite Control
Often called the “economic threshold”, research says that when the level of mite infestation reaches a certain level, the colony will experience decline and be less productive.
If mite growth is allowed to continue, the colony will die. What is that number ? Unfortunately, these numbers are “soft” and tend to vary somewhat from one region to another.
And, they vary from one expert to another and one year to another. They are guidelines not rules set in stone.
In my years of beekeeping, the “allowed” number for mite infestation keeps dropping. We are learning that it takes fewer mites than previously thought to harm bees.
In short, the honey bee colony can deal with a small number of varroa mites. It is not necessary (if even possible) to kill each and every varroa mite in the hive.
The treatment threshold describes the level of mite infestation that significantly damages the health of the hive.
Testing Varroa Mite Levels-Mite Counts
Before we can decide whether to treat our hives, we need and estimation of the number of mites in the hive.
New beekeepers often say, can’t you see mites on adult bees? Yes, you can. But, you can not use visual inspection to judge your mite levels.
You will not be able to see the vast majority of mites that are reproducing in the brood cells. Mites reproduce in capped bee brood cells. Do not rely on visual inspection!!
There are several popular methods for performing mite counts on your colonies. Choose one that fits your style of beekeeping.
Doing Nothing is Not A Viable Option for Varroa Mite Control
The new beekeeper will find many opinions on what to do about varroa mites. Lots and lots of opinions but not as much true research to back the opinions up.
The fact is that unless you have a very mite resistant bee you will have to do something to control varroa mites.
Whether you choose oxalic acid for mite control or one of the other treatment methods – do something.
Do not try to practice treatment free beekeeping unless you have bees bred for that management style. And know, based on the experience of other beekeepers in your area – that you can be successful.
How Many Varroa Mites are Too Many?
Most researchers agree that a varroa infestation rate over 3% needs management.
Taking ½ cup (measuring cup) of bees from frames in the brood nest yields roughly 300 bees.
If we find 9 varroa in this number of bees, you have a 3% infestation level. i.e. 9 mites/300 bees = 3 mites per/100 bees.
At this rate, I would definitely treat for varroa mites with an approved treatment method.
But what if you find a 2% infestation or even 1%. Can a single mite count give true results?
Some beekeepers promote multiple counts for accurate numbers. Then, you have to consider if you can take a chance on this lower mite count staying low.
Should You Treat Bees for Mites With Infestation Levels Below 3%?
Varroa Mites are a big problem in my region. Treatment is always necessary.
In years past, my hives with low mite numbers in July were full of mites and near death by November.
Still mite checks are a good way to monitor your colonies. Finding no mites or a 1% level may encourage you to watch and wait for a bit.
If the infestation level is 2% or greater, you have a decision to make. Mites counts do have value.
Varroa Mite Bombs in Late Season
Why do many beekeepers have low mite infestations in July and dead bee hives by late Fall? These large, robust colonies seem to dwindle or disappear very quickly.
Large numbers of dead varroa mites are often found among the dead bees and hive debris on the hive floor.
To begin to understand why this happens, we must look at the life cycle of each of the players in our game. Both honey bees and varroa mites have several life stages.
Life Cycle of Honey Bees
The life cycle (population growth) of honey bees is not the same as that of the mites. Varroa mites reproduce inside bee brood (capped cells containing baby bees).
The journey of the individual worker honey bee begins with an egg. Her journey from egg to adult is roughly 21 days. Queen bees reach adulthood in only 16 days.
But the drones, or male honey bees, are the favorites for varroa mites. Beginning as an egg, drones emerge from their cells on day 24. Drone bees spend 3 more days in the sealed cell.
Life Cycle of Varroa Mites
Varroa mites also go through several stages of development. A mated female lives about a month – during the summer season.
The mated female mite (foundress mite) rides around on an adult bee (worker or drone). She feeds on the bee by biting through the bee’s exoskeleton.
Phoretic Stage of Varroa Mite
This is called the “phoretic stage” of the varroa mite life cycle. You might see a mite on your bee-but usually the mites are on the underside.
This stage of life lasts 5-11 days when brood is in the colony. During Winter months with no brood, the phoretic stage can last for months!
The foundress mite jumps from bee to bee. This facilitates the transmission of viruses between the bees.
Many mite treatments only kill the phoretic mites – not the ones inside brood cells. Treating for varroa mites may need to be done in phases to catch mites out of the cells.
Reproductive Phase of Varroa Mite
When the foundress varroa mite is near a bee larva (almost ready to pupate), she drops off the adult bee and enters the brood cell.
Hiding under the brood food in the bottom of the cell, she escapes notice by the workers – who cap the cell.
Now the developing bee larva and foundress mite are locked inside the cell. Varroa mites can only reproduce inside the brood cell.
The female mite produces a male mite first and then a daughter or daughters inside the cell.
A worker honey bee cell is capped for 11 days (from day 7-21) . This allows enough time for the varroa to produce 1.5 females. (Yea, I know you cant have half a mite! – It’s a science average thing.)
The new female mite mates with her brother inside the cell. They feed on the developing bee, weakening it, and possibly spreading disease.
When the new bee emerges (assuming it is able to do so), the mother mite and her mated daughter emerge as well. The male mite dies inside the cell.
So, 1 varroa mite went in and about 11 days later – 2 came out. These 2 fertile female varroa mites enter a new brood cell and both produce a viable daughter.
The original mother will be nearing the end of her life cycle. But we still have 3 females inside the hive that originated from the first female or “foundress mite”.
Varroa mite numbers triple each month – by reproduction in worker bee cells.
Impact of Drone Brood on Varroa Mite Population
Drone bees have a longer brood cycle – 24 days. And, varroa mites prefer drone brood over worker brood .
Mites can identify the type of brood in a cell through pheromones. (They “smell” different).
On average, we can expect the mother mite and 2 viable daughters to emerge from a drone cell.
This gives us 3 mated females from 1 drone brood cell. These 3 mites find another drone cell. 14 days later, 8 viable mites emerge (because mom is at the end of her life cycle).
In just a little over a month (36-38 days) 1 foundress mite, became 8. Imagine how fast this reproduction can grow with hundreds of mites in hundreds of drone brood cells.
Varroa Mite Reproductive Explosion
The Varroa mite population in a colony will triple in a month when reproducing on only worker brood.
But with drone brood inside, the mite population can double every 2 weeks.
Mites prefer to ride around on house bees or “nurse bees” near the brood nest. That is why we take bee samples for mite counts from the brood nest area.
Studies indicate that for every phoretic mite on a bee, there are 2-3 more mites under the brood cappings.
In July, if you find 100 mites on the house bees, there are about 300 under the caps for a total of 400 mites.
If the mite numbers triple in a month, that means 400 mites (July), 1200 (August) and 2400 (September).
And that is when worker brood is used for mite reproduction not drones! Drone brood will allow even more mite reproduction.
When It’s too Late for Varroa Mite Control
The Beginning of the End for Bee Colonies
By mid July, many colonies have already started to slow down egg laying. You will still see a lot of bees inside the hive.
But more bees are dying than are emerging-resulting in a dropping population. (Your mite population is still tripling each month.)
As varroa mite numbers rise and bee brood numbers are reduced, a point is reached where every brood cell has a mite. And, older bee foragers are dying off due to age.
Emerging bees that take the place of foragers are not healthy. Some of them will die early or succumb to diseases that were spread by the mites.
Foraging is less effective and resources scarce. We have unhealthy adult honey bees trying to rear strong bees for winter.
These sick nurse bees are not able to properly feed the larva or even keep them warm. The overall health and longevity of every bee in the colony is now affected.
In just a few weeks, a large honey bee colony that seems on track for over-winter success can crash.
Older bees are dying, new adult bees are sick and short lived and larva are not being reared properly. It is recipe for a varroa mite crash disaster.
Mite Assessment-Hive Inspections
In this situation, outside observation of the honey bee colony was deceiving.
The colony looks busy with bees working. But the damage is being done inside until it reaches a point of no return.
This is how we hear of a colony that had a good sized cluster in late August and by mid-September the hive is empty.
We blame absconding when the real issue was varroa mites. Routine hive inspections can aid in finding problems that are being caused by varroa mites.
Watch for bees with deformed wings or mites present on drone brood between the boxes – both indicators of a problem.
Varroa Mite Treatment Schedules
You must decide how to handle varroa mite issues in your apiary. Closely monitor mite numbers and treat if necessary.
Don’t wait until Fall, it may be too late.
Also, very important – after you do your mite treatments, check to be sure that they worked!
Final Thoughts on When to Treat for Varroa Mites
Your location plays a part in deciding if you need to treat for varroa mites. And, the level of mite resistant in the bees in your hives.
Maintain regular hive inspections and look for problems but don’t rely on visual inspections for the whole picture.
Perform mite counts, listen to other beekeepers and learn what the latest recommendations are for acceptable levels of varroa infestation.
Mite resistant bee breeding is the hope for the future. I have not found a bee that can exist treatment free in my region, but I remain hopeful.
Until then, I will keep my mite count equipment handy. When is the right time to treat bees for varroa mites? Before, it is too late – that’s the honest truth – your hive will reach a point of no return.
Beekeeper Charlotte
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