LASI Talk on Varroa , OA application and hygienic behaviour.
Heard an interesting talk on Saturday by Hasan Toufailia who's doing a PHD at LASI.
Talk covered Varroa, treating methods and efficacy of OA using different methods and strengths and impacts of drone culling and hygienic behaviour of bees.
I believe the full paper will be published in the next month but I learned a few interesting things from that talk.
The study compared the efficacy of oxalic acid using trickle, spray and sublimation at 3 different strengths against control hives with no treatments added and looked at varroa knockdown, bee mortality, queen impact and hive performance 4 months later (quantity of brood). The study also looked at prevalence of DWV within the hive.
Im going from memory while I try and get hold of the slides/results so forgive me if I don't quote the OA strengths in absolute terms but from a trickle perspective they could be considered "weak", "standard" and "strong" mixes.
It's probably no great surprise that all methods of OA application were superior at varroa knockdown to doing nothing and all methods at most effective strength achieved around 97% reduction of mites within the colony.
In general terms, sublimation was the most effective and spraying the least, especially when looking in combination with bee mortality and colony strength 4 months later. In all cases the colonies where sublimation was used were stronger and typically had 1.5-2 frames of brood more than colonies where trickle method had been used and 2-3 frames more than where spay had been used. I don't believe that the full reasoning is understood but is thought to be that sublimation doesn't require the hive to be opened and is a quicker treatment to apply and that this may be the most reasonable cause.
The concentration of OA during application did appear to have some impact on queens, but I don't recall the exact figures for the methods concerned.
The basic conclusion is that OA is highly effective and that sublimation is the best method to apply the treatment.
Some other points raised looked at when to apply, before Christmas is optimal, which is a little earlier I think than many of us normally apply.
Removal of any brood present at that time was also considered beneficial. This was less around further reduction of mites as lessening the quantity of DWV present in the colony.
Removal of drone brood was also discussed while this is reasonably effective, a single frame taken out can reduce mite numbers by up to 50%, it was considered ineffective in isolation at controlling mite numbers even where multiple frames were removed in succession. If you assume a basic doubling of mite numbers with each generation, then a 50% reduction is a minor "blip".
Finally there was discussion of hygienic behaviour. Where colonies were considered >90% hygienic, they were effective at slowing the increase in mite numbers but there did not seem to be the suggestion that they were ever fully able to control mite numbers in isolation. However what they were also apparently effective at doing was controlling DWV within the colony, presumably through the ejection of infected brood.
Again I don't have the full figures to hand to expand on that at the moment but it was an interesting discussion.
I will see if I can get my hands on the slides and will be keeping an eye out for the full paper as I've been rethinking my IPM since the talk and will be looking a lot closer this year off the back of it.
