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Date: | Sun, 4 Apr 2021 14:19:52 -0400 |
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Last night I watched a YouTube on one of our members experience going without a top entrance this winter. During his discussion he mentioned that he was looking into the impact of higher levels of CO2 and mite mortality.
So this morning I did a quick google search to see what I could find:
Hives with restricted ventilation (Natural for those like me who subscribe to no top flow ventilation) will have significantly higher levels of CO2 (up to 200% higher). The mite mortality actually went up 60% vs the control (full ventilation) 37 vs 23 during the treatment period.
I would guess that my well insulated/sealed up colonies would likely have even higher CO2 levels (overall higher heating/meta rates required at Ts lower than the 5C from the study). I t would be interesting to measure mite drops during our 3-4 weeks of -30C to -50C cold snap and through out the winter. So is it really the brood breaks killing most of the mites (natural mortality) or the "hitched" - CO2 exposed mites (natural mortality + CO2 Kill) making the real difference. Folks with tons of ventilation would never get this added benefit.
All my colonies have survived our winter so far. The colony that went in with very high mite levels and signs of viruses, seems so far to be doing great. Once I get a chance I will do a OAV test treatment to verify post treatment mite drops. Still too cold and much snow to get into the hives.
Reference: https://pubmed.ncbi.nlm.nih.gov/26453704/
The Potential of Bee-Generated Carbon Dioxide for Control of Varroa Mite (Mesostigmata: Varroidae) in Indoor Overwintering Honey bee (Hymenoptera: Apidae) Colonies, Rassol Bahreini 1 , Robert W Currie 2
<<When ventilation was restricted, mean CO2 level (3.82 ± 0.31%, range 0.43-8.44%) increased by 200% relative to standard ventilation (1.29 ± 0.31%; range 0.09-5.26%) within the 16-d treatment period. The overall mite mortality rates and the reduction in mean abundance of varroa mite over time was greater under restricted ventilation (37 ± 4.2%) than under standard ventilation (23 ± 4.2%) but not affected by stock of bees during the treatment period. Selected bees showed overall greater mite mortality relative to unselected bees in both experiments. Restricting ventilation increased mite mortality, but did not affect worker bee mortality relative to that for colonies under standard ventilation.>>
Note: The paper uses an active ventilation of 14.4L/min (~3min air change of a single deep enclosure volume) and 0.24L/min for restricted hives. The active ventilation seems very high based on my previous theoretical flows calcs. The restricted flow numbers to be in the correct range.
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