Having done Demaree and Horsley board, I have sealed queen cells which will hopefully hatch and mate. Up to 8 days after she starts laying, I will have a colony with no sealed brood. I have the option of an apiary in a varroa-free area, and although I currently have no varroa in those colonies, I have varroa in others in the apiary (at very low levels) and would like to vapourise with ‘oxalic’. Is this advisable with a young queen, or should I wait (how long?) and vapourise a number of times (how many and how many days apart?).