Tracheal Mites are the forgotten mite. Why? We have "tracheal mite 
resistant bees". We cannot see it unless we do some scope work. If a 
colony fails, since Varroa is so common now, VM gets the blame even 
though it might have been TM (or a combination of the two). After the 
failure, only Varroa will be present, so there is no problem blaming it. 
TM disappears with the bees.

When we talk about VM or TM killing a colony, as all on this list know, 
we are really talking about the disease they spread that does the killing.

TM  causes disoriented bees that do not act like bees should. They 
vacate a hive in the dead of winter with temperatures well below 
freezing. TM spread when bees are crowded, such as in colonies on a 
truck being moved from place to place. As Bob noted, TM "vectored" 
disease can spread under those conditions. Winter also causes crowding 
as does bad weather or a lack of nectar. Those conditions also allow 
disease and TM to spread.

In the past many years, we have taken TM resistance for granted. The 
problem is, we have also imported bees from TM free places like 
Australia or Hawaii or have bred from TM resistant bees which could 
easily have lost that resistance over time and open breeding. We, in all 
probability, do not have TM resistant bees in most of the US.

TM seems to operate in cycles. You have large winter kills one year then 
it disappears for as many as five years or more. It seems intuitive that 
the kills are related to the mites dying with the bees and they build 
back up, but it is also related to the weather in the area. As noted, 
bees can be confined in good weather with a lack of nectar, or bad 
weather in the normal growing seasons. TM can build up not just in 
winter. You can also have the normal cycle of resistance, in this case, 
bees. You have the massive die off of TM susceptible bees, the remainder 
are TM resistant. Over time, TM resistance fades since there is no 
pressure, and the bees are again TM susceptible.

Another interesting fact is that Varroa have their greatest growth 
during maximum brood rearing while TM is just the opposite, when bees 
are confined and no nectar is available.

TM and VM can be in a colony at the same time. The virus or combination 
of diseases that cause TM symptoms could be started by the TM and helped 
along by VM. As I hypothesized (guessed) before, there may be a much 
lower threshold for Varroa to spread disease if TM is also present. You 
could have acceptable VM thresholds but the additional TM may allow a 
rapid spread of disease especially in confined environments found in 
commercial operations. The result is TM behavior- disoriented bees 
flying off to die and rapid colony collapse (helped along by Varroa). 
The only thing missing is the lack of robbing. I can add another 
unscientific observation. My TM colony which was loaded with honey was 
not robbed by the adjacent (four feet away), active colony. There was 
not even one bee on the hive. That means nothing but it is interesting.

Bill Truesdell
Bath, Maine

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