Intriguing how opinion and dare I say fashion changes, Khalil Hamdan, following the techniques of a Dr. Kamran Fakhimzadeh, University of Helsinki, Finland in 2000, declares plainly that icing sugar dusting “has no adverse effect on adult bees and the capped brood, and the sugar particles do not enter the spiracles and their tracheal ducts in the treated bees. The technique can be used at any time, even during a honey flow, and as often as needed...” he goes on to say that “Formic and oxalic acids are strong and toxic, result in queen loss, hurt the brood a bit and leave a residue and that “Formic and oxalic acids cannot be used when it is warm or hot, whereas powdered sugar...” concluding that “The method is in practice in the USA, Germany and Ireland, and most who have used it say it works.”
I prefer to follow more informed science rather than 20 year old dodgy papers languishing on the internet.