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Date:         Fri, 24 Nov 1995 10:09:59 -0700
Reply-To:     Discussion of Bee Biology <BEE-L@CNSIBM.ALBANY.EDU>
Sender:       Discussion of Bee Biology <BEE-L@CNSIBM.ALBANY.EDU>
From:         Jerry J Bromenshenk <jjbmail@SELWAY.UMT.EDU>
Subject:      Control of Tracheal Mites


After 2 1/2 yrs of dissecting 20,0000 honey bees to look for tracheal mites, we are in the final stages of data processing and polishing articles on the research.

We have also finally gotten our PC BEEPOP model completely re-written in C and C++ with a full mite simulation module - we've promised this before, but the model got so big and complex that my programmer's got over their heads in terms of being able to de-bug it. However, that changed in May when a new graduate student in computer science joined our research team. He got it working and we now trust it enough to start the test simulations. I expect to release a beta test version around Christmas time.

In the meantime, some observations that may be of interest:

1) Tracheal mites appear to respond to cumulative stressors. The colonies starting with low levels of mites or low levels of environmental stress (in this case metals from a lead smelter) ended up surviving the longest and having the fewest bees with mites and the lowest number of mites per bee. As the stress and/or initial number of mites increased, the colonies died quicker (by as much as 6 - 8 months) and had more bees with mites and more mites per bee.

No surprises here, but it certainly shows that the metals did not kill mites faster than bees.

2) Tracheal mite levels varied greatly over time in 48 test colonies in Montana and 12 test colonies in Arizona. Bottom line is that I would be willing to wager that no one can predict mite infection levels next month based on levels this month - and if you manage that one, you certainly can't predict them 6 months from now.

In other words, worrying about whether to sample bees at the front entrance versus the honey supers to get the "best" estimate of mite levels (grab that last decimal point) is a mute point when the colony may have many times fewer or more mites next month.

The data looks like a roller coaster. Yes, some colonies start low and stay low and some start high and stay high, and some progressively increase, but most jump around all over the place - like the colony that had 5% of the bees infected in December and died in April with virtually all of the bees with mites and most of these bees had mites in both tracheae.

3) Tracheal mite levels seemed to parallel varroa mite levels or vice versa. We started with colonies treated with Apistan that had traceal mites at different levels. We did not treat for any mites during the 24 months of testing. By the second year, all colonies had some varroa mite, but the smelter site had the worst infestations of varroa. More importantly, the higher the numbers of tracheal mites, the higher the numbers of varroa mites - at most sites.

4) We saw "PMS" in colonies with both mites and in colonies with mainly tracheal mite. Oh, I also agree, a most unfortunate acronym in this P.C. age.

5) Here's the kicker - our model outputs agree with Royce and others that swarming may control tracheal mites and that supressing swarming may encourage this mite ------ but our models go further and suggest that we are treating at the wrong time of year.

Granted, if you have heavy tracheal mite infestations, your bees may have to be treated in the fall to "save" the bees, and yes, it is easier to treat in the fall after the honey is off (and no chance of contamination of honey).

But, according to our preliminary simlulations (and I reserve the right to change my mind on this one if we find any more bugs in the model), killing 30% of the mites in spring and early summer will wipe out the mite population. Killing 20% of the mites will keep them in check (low levels). On the other hand, treatments in the fall have to kill virtually all of the mites if you hope to get long lasting control, and over 85% of the mites have to be killed to get any chance of suppression.

Killing 30% of the mites in the fall does no good at all. The model and our data and the data of others demonstrate the potential for incredible numbers of mites in bees in fall and early winter. The percent of bees infested is not nearly as important as the total mite load - we've seen bees with over 60 mites per bee, compared to 6-10 max in the summer.

That's a lot of mites. In cold climates like ours, brood rearing suspends from late Oct thru late January/early February. Looks like all those mites just keep producing mites with no where to go (no nice young new hosts). But, with the first wave of new bees, the mites can transfer.

The model says that is the time to hit them, wipe out mites in the "old" hosts and protect the new bees. Reduce the mite levels during the spring build up and the bee colony will out pace the mites. At any other time of the year, this is difficult to do without almost total eradication of the mites - which is asking a lot of the fumigant.

Based on the preliminary results of a "still" unverified model, I DON"T SUGGEST YOU COMPLETELY CHANGE YOUR TREATMENTS - especially if you have several thousand colonies. However, you might want to try a spring treatment on some of you colonies and see if it works better.

The other option is to not treat at all as suggested by Erick Erickson. Let your bees die and re-establish your operation on the survivors, but I doubt that most of us can afford that drastic approach.

Mite resistant queens may be out there, but I haven't been convinced that they are readily available and certified ( we've seen many of these so-called resistant bees come down with heavy mite loads - in one case we had "resistant" queens with 100-200 mites per queen. They were resistant in the sense that they were still alive - not doing much in terms of producing offspring, but still walking).

Oh well, food for thought as you digest yesterday's turkey.

Jerry Bromenshenk The University of Montana Missoual, MT

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