In a previous post we reported that we’d uncovered a tremendous Varroa mite infestation in the largest of our bee hives, the Salvia hive.  It was clear this colony was in jeopardy.

This drone (male) is one of many in the Salvia hive that hatched with a mite attached to its thorax (click any image to enlarge)

Treating Mites

There was some evidence of hygienic behavior in these bees, as they were removing at least some of the mite infested brood.  However, due to the overwhelming level of mites in the Salvia colony, we elected to treat for Varroa using Thymol, an organic oil.

This pupa, in the strawberry-eye stage, has just been uncapped by the worker bees, and will be removed from the brood nest. Such pupa are often affected with mites, or viruses.

When choosing to treat for Varroa, it’s important to treat early enough in the season that the colony still has time to build up its population of winter bees.  Winter bees are unique in that they have longer lifespans than summer bee populations, and a colony’s winter survival depends upon the presence of a strong population of these long-lived bees to get them through to spring.  In this area, mid-August is the time to apply any mite treatments, so the bees will have at least two full brood cycles to produce their winter bees before the foul weather sets in.

Thymol is derived from the oil of the Thyme plant

Any treatment has the potential to cause harm within the hive, even treatments with organic oils and acids.  How and when treatments are applied can affect the degree of potential brood kill, or Queen loss, but whether or not either happens isn’t always predictable.  It’s important to know that many of the products available for treatment of Varroa work by releasing vapors that are noxious to mites within the hive, and the amount of vapor released is affected both by the dose applied, and ambient hive temperatures.  As such, when treating colonies it’s important to be mindful of weather conditions during treatment.

Thymol is an organic oil that is used for treating colonies infested with Varroa mites (Varroa destructor)

There are various formulations of Thymol on the market, including gels (ApiGuard®), crystals, wafers (Api Life VAR®), and strips (Thymovar®, Thymomite®).  We elected to use Thymol strips, which weren’t readily obtainable here, so while we waited for their arrival, we resorted to interim measures of mite control.

Finally, the Thymol arrived.  Before applying the strips, we inspected each colony, and removed the drone frames in the Salvia and Rosemary hives.  The Lavender and Chamomile colonies appear to have already ceased drone production for the season, and both of their drone frames were filled with worker brood cells.

The drone frame in the Chamomile hive contained capped worker brood, so we replaced that frame

It’s important when treating colonies, even with organic oils or acids, to harvest any honey that needs to be harvested BEFORE treating.  Although the treatment isn’t toxic per se, it does leave a residue in honey and wax for some weeks after treatment, and may taint honey flavor.

Capped honey frame - If we were going to harvest honey, we would need to do so prior to treating the colony, as the honey's flavor will be altered by the Thymol

The honey stores in each colony were recorded, and as this is the first season for these colonies in the apiary, and our weather has been generally cold with below normal temperatures for this season, all of the hives seemed relatively low on honey, so we elected not to harvest any this year.

Even our largest colony only had 10 medium frames full of honey and nectar. Our smallest had only 1.

We noted the number of brood frames in each colony before deciding how much Thymol should be placed within each hive, per the manufacturer’s recommendations, to prevent over-treating the colony.  As it was put to us some time ago, all Varroa treatments involve trying to “kill a bug, on a bug”.  The goal is to eliminate the parasite, not the patient.

For the smaller colonies, Chamomile, and Lavender, we treated with one half of one Thymol strip.  The half strip was cut in two, and the two pieces placed at the top of the brood nest in the corners furthest from the entrance. Neither of these colonies had particularly high mite counts.

For the two large colonies, Salvia, and Rosemary, a whole strip was divided in half and placed similarly.

The Thymol strip was placed on the frames at the top of the brood nest. Bees in the area of the strip retreated immediately

It was apparent as soon as the strips touched the frames that the bees were offended by the strong Thymol odor.

The hives were reassembled, the screened bottom boards were closed (using the sticky boards), and entrance reducers were placed.  Too much airflow during treatment reduces the effectiveness of this Thymol treatment.

The bees were initially confused by the entrance reducers, but soon adapted to having a smaller front door.

It didn’t take long to see some increased activity at the hive entrances, especially in the colonies that received the higher dose of Thymol.  Overall though the reaction to the Thymol odor wasn’t as much as I’d expected.  It may have helped that we installed the strips late in the afternoon, as the fog was rolling in and air temperatures were starting to cool.  After 24 hours hive activity seemed to have returned mostly to normal.

As we left the apiary, we could see the two hives on the left (which had the higher dose of Thymol applied) had much more activity around the entrance

After two weeks, we removed the bottom boards, cleaned them off, and reinstalled the boards for a 48 hour mite count mid-treatment.  The mite count in Salvia has decreased slightly, from 116 mites per 24 hours pre-treatment, to 103.  Not a particularly significant reduction yet.

Varroa mites on the sticky board

So the question is, how will we know if our Thymol treatments have been effective?  One thing that is important to note is that it’s apparently typical when treating with Thymol for there to be a delay in the drop in mite count.  This makes sense when you realize how Thymol works.  Thymol is effective against exposed Varroa mites.  Those on adult bees, newly hatched bees, or lurking on comb before cells are capped, but it doesn’t reach the mites trapped inside the capped brood cells.  For it to be effective, it must remain in the hive for a minimum of four weeks, so the vapor is present through at least one complete brood cycle.  So after two weeks, we’re only now half way through treatment.

Any mites entombed in the cells with the developing pupa (yellow arrows) won't be affected by the Thymol vapor until after the bee hatches

Per the manufacturer’s directions, a second dose is to be applied after two weeks, without removing the first strips.  We’ll continue with treatment and apply the second dose of Thymol this week, and repeat the counts again in another 14 days to see if the mite population shows evidence of decreasing, and then re-evaluate our hives at that time, and decide whether to continue for one more round of treatment.

Thwarting Robbers

As if fighting Varroa mites isn’t enough for the bees to cope with, we’re sliding into late summer, and the native flower blossoms have faded.  Late summer in this area typically means a nectar dearth, and with that comes ‘robbing season’.  Bees either from neighboring or nearby managed or feral colonies will exploit the stores of weaker hives, often cleaning out weak hives entirely of stored nectar and honey if given the chance.

Honey is honey, and when food supplies are short, bees will take it anywhere they can find it, even from their neighbors!

During the inspection just before we applied the Thymol strips, we noted some early signs of robbing.  Hive boxes that were removed during the inspection, if not immediately covered, were subject to bombardment by bees from our other hives.  Bees were wrestling on the landing boards and on the ground, as the guards defended their stores.

Bees aren’t the only robbers though. Last Saturday afternoon I noticed a few yellow jackets lurking around the hive stand for the first time this season.

Yellow Jacket Wasps (Vespula sp.) are so aggressive that we frequently see them fighting each other

In some areas yellow jacket attacks on hives can be the greatest threat to an established colony.  We’ve had a history of having some rather formidable wasp nests here in the past couple of years, so we knew we needed to be alert to their presence in the apiary.  They’ll steal pollen, raid honey stores, kill brood, and viciously attack adult bees.  They typically will start with the weakest colony and then proceed through the apiary.

Although robbing screens are available commercially, we really need to install them as soon as possible.  Fortunately, at a Bee Guild meeting last fall, Dr. Eric Mussen, Extension Apiculturist from the University of California at Davis, had provided attendees with a handout describing a design for a homemade robbing screen.

A robbing screen positioned over the hive entrance is intended to prevent non-resident bees from reaching the hive entrance. It may also be effective against yellow jackets

This screen could potentially thwart both neighboring honey bees, and yellow jackets from raiding hives.  This screen, placed across the entrance, would permit resident bees to come and go, but neighboring bees get confused when they land at the entrance, and can’t find their way in.

We spent Saturday night constructing four of these screens, one for each hive, to install first thing Sunday morning.

Sunday morning we installed a screen on each of the hive entrances

In the morning we found 3 yellow jackets outside the entrance to the Salvia hive, fighting over a dead bee pupa.  What wasn’t clear was whether they had removed the pupa from the hive themselves, or if this was one that had been dragged out of the entrance by an undertaker bee.  Regardless, the wasps were fighting furiously over it.

Soon thereafter, an adult bee with deformed wings rolled out of the entrance of the Salvia hive, and onto the ground.

As soon as the honey bee (right) landed on the ground, this Yellow Jacket attacked her

No sooner had she hit the ground, than she was immediately attacked by a yellow jacket, and killed.  After not seeing these wasps for most of summer, it’s clear that it’s now very much yellow jacket season here.  The screens have now been installed on all the hives, and will hopefully help to protect the colonies, their stores, their brood, and take the pressure off of the guard bees at the entrance.

Each screen cost less than $4 in materials to make.  We used some scrap wood, and metal vent screening (the metal seemed more sturdy than plastic window screen).  Each screen is anchored to the hive with a hook-and-eye latch.  Although it led to some air-traffic confusion initially, the bees have adjusted to the screens very well.

Resident bees climb the screen and fly out to the field, and learn to fly down to the entrance. Robbers land on the landing board and walk forward, getting stuck on the outside of the screen

Now we’ll just have to see how effective they really are at excluding the yellow jackets.  We’ve found some very large nests on the property in the past, and if necessary, we’ll place traps to help decrease their population near the apiary.  It would be awful to succeed in reducing Varroa mites in the apiary, and then lose a hive to marauding wasps!

If there’s one thing that stands out to us as relatively new beekeepers, it’s the constant barrage of challenges that honey bees must face every day.  Between mite infestations, hive incursions from ants, wasps, wax moths, and small hive beetles.  Not to mention raids on hives from curious wildlife, and the hazards of pesticide-laden flowers.  It’s made us appreciate just how undervalued honey really is.