Though this is a bit outside our normal fare, I thought it would provide some anecdote relative to the development of resistant populations, at least surrounding our little dot on the globe.

As I enter year 6 of a TF experiment here in Western Kentucky, I thought it might be worthwhile to look back on the past five years and identify some of the more salient observations that have risen to the surface in studying this local population.

Looking back at the last year (April 1st cut-off), I lost ten (10) colonies: Three (3) summer queen failures and seven (7) overwintering losses.

As of today I have thirty-nine (39) colonies so the effective total year survival percentage is right at 80%.

Amalgamating this with the previous four (4) years I have a 5-year survival average north of 80%, which I think is quite respectable in a TF context, particularly given that I do not provide any supplemental resources as a rule.

A few things I now know after having studied this population:

1. I would no doubt have a higher survival percentage and better yields if I provided external support to the colonies in their battle against varroa and the viruses they vector.

2. The population is not 'bullet-proof'. It is often the most populous and productive colonies that suffer the most from lack of external support.

3. The population at-large is able to put up a respectable defense against varroa and viruses on their own.

A few things I am learning about this population and hope to know more about in the coming years:

1. There appear to be several resistance and tolerance factors working in concert to help forestall varroa damage. Those I know about are mite biting, uncapping/recapping, swarming, brood throttling during dearth periods and viral tolerance. There are likely others but I've not been able to empirically identify them as yet.

2. It appears that the prevalent DWV strain in the population is DWV-B. This may in-fact prove to be a less virulent strain and may be part of the survival story.

3. The most straightforward predictor of survival appears to be the 72 hour mite drop figure at the Summer Solstice- but even this is not 100% accurate as the chart attached outlines (hopefully it comes through). Several colonies persist despite higher mite loads and other colonies drop out, even with low mite loads.

I continue to be amazed at the resilience of these amazing insects.


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