What do you mean by an essential oil? I assume you are considering adding some to your maggots! I have used krill powder, vanilla flavouring, curry powder and the like with varying and dubious levels of success! I like to keep my maggots dry so add nothing! Glugs, hemp oil etc I only add to pellets and then sparingly!
Powders can be applied liberally but best done on riddled maggots the day before they are needed in order for the flavour/colour to be absorbed alledgedly!