The abstract of the study by Ellis et al. cited by grozzie gives very little information.What did stick out was that a brood break IN THE FALL resulted in colony deaths.
Well no kidding!!
In FL ,by the fall,with no other Varroa control,I'm bet those hives are ready to crash with very high V. loads.
I've got a friend that does have access to the full study at that link, so got them to send me a pdf. I'm not permitted to share it publicly or I would. But I can summarize the points that caught my interest.
Study was done September 2016 in Gainesville Fl, so I dont think any wintering considerations would matter, it is my understanding bees brood year round in that area. Prior to the start of the study the colonies were equalized over a period of some number of weeks to reach a starting strength of 10 frames bees with 7 frames of brood. Once the experiment was started, there was no more transfer of frames between colonies. 10 colonies were assigned to each group.
The 'treatments' were as follows. One application of OAV. Three applications of OAV at 1 week intervals. OAV applications were as per the label. Brood interruption by placing the queen into the Var-Control cage for 24 days. All combinations and permutations were tested. One set of colonies got no treatment at all for negative control, another set got apivar, a positive control. Final results were tallied up 62 days after the start of the study. Lots of graphs showing population size and mite drops thru the study, but the one thing I've homed in on is the table showing colony survival rates,
Neg. Control 0.7
OA-1 0.5
OA-3 0.7
BI 0.1
BI-OA-1 0.4
BI-OA-3 0.6
Amitraz 0.999
To calculate odds ratios, survival cannot equal 1. Thus, 100% survival is presented as 0.999. OA = oxalic acid applied via vaporization, BI = brood interruption
achieved by caging the queen, Amitraz = amitraz applied via Apivar strips, 1 = one application, 3 = three application, neg. control = negative control.
The discussion mentions a few things. All queens in the cages were still alive at the end of the brood interruption if the colony was still alive. Discussion also mentions that they felt the 1g application rate on the label was insufficient.
But my own takeaway is this. Even if insufficient, the colonies with OA got the same treatment. The colones with Brood interruption fared more poorly than those without, particularly noticeable comparing the 'do nothing' colonies with the 'only a brood break' colonies. 70 percent survival vs 10 percent is NOT insignificant in my books. Those that got the two variations of OA show the same trend, without brood break did better than those with a brood break. I agree with those suggesting the 1g label rate may be low, I always use 2g because that's what it says on my labels. BUT, application rates aside because they are equal in this study, the colonies that got brood breaks did poorly, those that didn't get brood breaks did better. It doesn't mean they did good, it means they didn't do as bad as those with brood breaks.
Here is another quote from the discussion which shows that the differing performance wasn't because they just ignored the colonies for 62 days.
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We observed high colony mortality in many treatments, despite diligent colony management to alleviate the side effects of the treatments. As colony populations began to decline, they were fed sugar syrup and had entrance reducers placed on their hive entrances to reduce robbing. Furthermore, small hive beetle (Aethina tumida) traps were added to all colonies to reduce the effects of beetle damage.
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And farther down in the results discussion
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Other researchers have observed increased efficacy in Varroa control when brood interruption was combined in conjunction with OA treatments (Wagnitz and Ellis 2010, Pietropaoli et al. 2012, Lodesani et al. 2014, Gregorc et al. 2017); however, we did not observe any benefit of brood interruption during our experiment. In fact, in all cases in this experiment, more colonies died when brood rearing was interrupted. To our knowledge, all other published experiments combining OA treatment and brood interruption appliedthe OA via the trickling method rather than vaporization.
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So if you look at this part of the discussion, they are clear here too. Another interesting tidbit, all the other researchers that did this used dribble method, not vaporizing. If they followed the label for dribble method, they would put almost double the amount of OA in per each colony assuming 10 seams of bees and 50ml per seam.