I sprayed a severe rosy woolly aphid infestation on my apple tree with a mixture of crushed garlic stepped in used cooking oil - left for 2 days in the fridge, then added to something like 1 part mixture to 10 or 20 parts water.
I sprayed it on the apple tree, but it did not seem to control the woolly aphids. However, I have also noticed that there were no ladybirds around this year. Would a garlic and oil mixed with water spray be harmful to ladybirds?
One of the reasons why your garlic oil concoction didn't work is that you didn't have a teaspoon of soap to work as a wetting agent. Just using oil and garlic alone wouldn't have been good enough for it to stick to the leaves and plant.
Your recipe is basically a white oil, with the addition of garlic. Which should have worked as aphids hate the smell of garlic, so like you, I am wondering why it didn't.
Spraying white oil directly onto most insects will be very effective, but you really have to be bang on target for it to work.
I am also wondering if you reapplied your mixture after it had rained.
One caution with white oil is that you have to apply it when there is cooler weather about, as it can easily burn the leaves of your plants in hot weather.
So to answer your question about the ladybugs, unless they were there too when you sprayed your apple trees, they would have been unaffected.
As you can see from the article on natural pesticides, there are other methods of killing woolly aphids. Perhaps next time, you can try an alternative that may be more successful.