In a blender*** combine:
1 cup water
1 tablespoon tea tree oil (for nosema control)
1 teaspoon lemongrass oil
1 tablespoon spearmint oil (for mites)
Blend until thoroughly emulsified, approximately 5 minutes. (By emulsifying with the blender, there is no need to add a chemical emulsifier.) Pour the emulsified solution into a half gallon jug and add water to make 2 quarts. (Do not heat EOs, as this causes the oil to dissipate.) This is the concentrate. It will keep for months. (A jug of concentrate will make 8 gallons of 1:1 syrup at the dilution suggested by the WVU researchers' formula for controlling varroa mites by feeding EO syrup.)
Add 1 cup concentrate to 1 gallon of cooled sugar syrup.
***Note: EOs are strong and so concentrated that they will damage the seals of the blender unless you rinse them cleanly away after blending.