will an oxalic acid vapouriser kill bee larvae

i have always thought that you should use oxalic acid in a vapouriser only when there is very few larvae or none. but having seen a guy on utube say that you can treat them any time, it made me
 wonder. i have checked all of my hives a couple of days ago i hefted (lifted the hive from the back ) them to see if they are heavy or light and also check whether they are damp under the roof. the temperature was about 9deg. centigrade
some of the bees didn't react at all but some did good job i was kitted out properly. i also put on some fondant in to the hives which were light. i don't like feeding sugar or fondant but i'd rather have my bees survive the winter. i am woking towards finding a strain or strains of bees that work well in my area the ultimate would be for the bees to produce enough honey for themselves with some surplus for me. but also for them to cope with what ever is thrown at them eg. variable weather,disease and also less swarmy, perhaps also then they could be left undisturbed for longer periods.

my first thoughts

i have spent this year showing a group of new beekeepers how i keep my bees. i might as well explain my ideas firstly i use Tim Rowe's rose hive or commonly called the osb (one size box), i also do not use a queen excluder. I also don't believe in marking the queen or clipping her wings. Drones are far to important to use them as some form of varroa treatment so i encourage the bees to have the number of drones they need.