This is very easy to do and it works a treat!
2 tsp dishwashing liquid
3 tsp vegetable oil
1 cup water
Add oil and soap to a spray bottle and fill with water. Shake well before each use. Spray the oil soap directly on unwanted pests. The spray smothers them so they need to be as coated as possible.
You can add garlic to your oil soap spray which will help deter pests as well. Soak 12 cloves of chopped/crushed garlic in vegetable oil (have oil cover all of the garlic) for 24 hours. Strain and add in place of regular vegetable oil in recipe.