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When to Treat Bees For Mites?

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When Should I Treat Bees for Mites

Deciding 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. By the time you see mites on the bees, it may be too late.

Handful of bees dead from varroa mites image.

We can only imagine how wonderful beekeeping must have been before varroa mites arrived in the United States. Of course, there were still challenges faced by beekeepers but everyone agrees it was an easier time.

Once varroa arrived in force, modern beekeeping changed. And at least for now, any one interested in keeping bees must have a plan to deal with this external pest of the honey bee.

picture of varroa mites in beehive when to treat for varroa

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 are 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 areas 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.

The beekeeper should learn how to monitor mite infestations in the hive. From there, you can decide what if any action to take.

No Treatment Method

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 some type of treatment.

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.

Fall Absconds or Heavy Mite Loads?

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.

A bee larva being parasitized by varroa mites image.

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.  In Best Varroa Mite Treatments, we talk more about the approved methods.

Beekeepers with a lot of hives may find it expensive to treat their hives. In the interest of saving money, work and stress for the bees, researchers have developed treatment thresholds.

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. We can still use them as a guide. But remember, acceptable mite levels 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

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.  Do not rely on visual inspection!

By the time you notice mites on your adult bees it may be too late to save the colony. Use one of the approved methods for performing mite counts on your colonies.  The sugar shake and alcohol roll are two common testing methods.

How Many Varroa Mites are Too Many?

After performing your mite count with one of the methods in the link above, its time to consider how big your mite problem is. Most researchers agree that a varroa infestation rate over 3% needs management.

Using a standard ½ cup (measuring cup) of bees from frames in the brood nest yields roughly 300 bees. After conducting your sugar shake, and counting any varroa we are left with these numbers.

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.

But, what if you find a 2% infestation or even 1%. Can a single mite count give true results? Some beekeepers promote multiple mite counts for accurate numbers.  However, few beekeepers do multiple counts.

Should You Treat Bees for Mites With Infestation Levels Below 3%?

In regions where mites are known to be bad, treatment is always necessary. Finding no mites or a 1% level may encourage you to watch and wait for a bit.  Depending on the time of year you may be able to skip mite treatments for a while but it is a risk.

If the infestation level is 2% or greater, you have a decision to make.  Depending on your schedule and the time of year, the beekeeper may going ahead and implement a treatment to keep the mite population low.

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.

Beehive debris with dead varroa mites on hive floor image.

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.

Varroa mite floating in brood food of a cell image.

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 bees-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!

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.

Varroa mites inside bee brood cell in burr comb image.

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.

Is it Too Late for Varroa Mite Treatments?

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.

Varroa Mite Treatment Schedules

In most cases, an early Spring treatment may be necessary. This gets mite loads down before the honey flow begins.

Monitor mite levels during the season until mid Summer. If not required before then, a mid-late season treatments lowers the number of mites and allows the colony to raise healthy bees for Winter.

Don’t wait until Fall, it may be too late. Perform an approved mite treatment and after you do your mite treatments, check to be sure that they worked!

Final Thoughts on When to Treat for Varroa Mites

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. 

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.

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