Varroa Problems?

by John Mumford

I remember as though it were yesterday, the 21st September 2004 when I met Peter Heath our SBO at High Trees Farm. Peter needed to inspect some colonies due to a local outbreak of AFB at Standon. And I was there because the beekeeper was in hospital having his gallstones out.

I arrived a few minutes before the 2.30pm appointment to find Peter with the rear doors of his van open, sitting having his sandwiches.  It was a grey, chilly, and very windy afternoon and after our initial greetings Peter said to me, "it’s not a very nice day for it John!", and added, "do you think we ought to put it off till another day, it’s a bit windy!". Now my philosophy has always been that if it has to be done, then do it, and do it quickly. They weren’t my bees anyway! 

The beekeeper had suspected there was something wrong with his bees and had asked Peter to do a CSL. OP Resistance Test on three of the colonies.

I was given charge of the smoker and stood upwind of the hives to shelter the bees as much as possible while Peter did his stuff. It’s an experience to watch Peter handle bees, and several times he said, with a little urgency, "keep them down John". The bees were as good as gold. No sign of AFB, but all the signs of a heavy Varroa infestation were plain to see (bald brood, starved brood, tatty wings), the lot. Peter duly collected the samples of bees for the CSL Varroa OP Resistance Tests as he went round.

Peter phoned me that evening, and my heart sank as he confirmed that he had found up to 65% OP Resistant Varroa Mites in one sample, and how he was lining the mites up in rows of ten to make counting easier.

Next day I started phoning around to find an alternative treatment. Both Oxalic and Lactic Acids were expensive and difficult to get, and for best effect depended on a broodless period. I didn’t think the bees wouldn’t survive that long anyway!

I had a recipe for Thymol Grease Pattie, and some Thymol Crystals somewhere, and so with no experience to go on we decided to give it a try. One badly infected colony was the first to get a Pattie - 70 mites dropped in the first hour - it worked! The rest of the colonies received Patties and we couldn’t wait to do a mite drop count the next day. The next day we had difficulty counting the 500 or so mites that had dropped overnight. Most of these colonies survived the winter.

Peter did a lot of mite counting that Autumn and in the following weeks he established that resistant mites were widespread but the amount of resistance was variable from one apiary to another, and even from hive to hive within apiaries. A lot of bees died that winter, and so did their mites.

This year I was late in putting my Grease Patties on. I had noticed that one of my colonies was dropping more mites naturally (35 per day) than I would normally expect. They got a Grease Pattie on the 5th September. By the 13th they were dropping 100 mites per day and I thought everything was OK. On the 28th they were still dropping 80 mites per day, and it was then I saw a bee with tatty wings drop out of the entrance.

I remembered that I had an old packet of Apistan somewhere in the garage. I eventually found the re-sealed packet with just 3 strips and a 2006 expiry date. On the 4th October with nothing to lose that colony and two others, (how can a beekeeper have favourite colonies), got one strip of the Apistan each, right in the middle of the bees. Next day there were 220+ mites on the floor. By the 12th the mite drop was 60 per day, and on the 18th, 14 days after putting the Apistan strip in, the daily mite count was down to 8, (1074 mite drop in 14 days).

It appears that Apistan has regained some of its effectiveness, but it should not be relied upon as a sole treatment just in case the mites in that particular hive still have a high degree of resistance. When Apistan works, it works extremely well, and no Varroa treatment could be easier to apply. It is NOT temperature dependant and so can be used at any time of the year when honey supers are not present.

I now have a fresh supply of Apistan to treat my other colonies. It doesn’t matter how the mites are killed, providing the treatment doesn’t harm the bees or leave unwanted residues in the hives. I doubt if this 'GET OUT OF JAIL FREE' card will still work so well next year.

I have heard quite a few reports this Autumn about high residual mite populations in colonies that have had a Thymol based treatment, and that some colonies have dropped over 2000 mites when Apistan has been applied. Varroa mites have never developed 100% resistance to Apistan, only just sufficient resistance for the residual mite population to kill the colony and themselves in the process. It’s a poor parasite that kills its host. If a Colony has 20% OP Resistant Varroa Mites the other 80% are removed quick sharp with Apistan.

The efficacy of Thymol based Varroa treatments are temperature dependant. And the method of application is perhaps even more important than treatment itself. I have always thought that a 4 week treatment of Apiguard is not sufficiently long for good Varroa Mite Control.

Varroa Mites per se don’t kill bees it’s the viruses that the mites transmit from bee to bee that do the damage. A small mite population with a lot of virus will do more damage than that of a large mite population and no viruses. Just a few particles of ABPV injected into a bee will result in the death of the bee in a few days. These bees are unable to fly; they crawl away to die and are not normally noticeable at a casual glance. At this time of year they are probable taken by wasps and birds anyway.