This is going to be difficult to find because the information is so specific. You should probably google for "Scholarly Articles" on Insect Anatomy and Aphids and Ladybugs separately.
Here's some good info to start with. And you can probably google search on various technical names for the parts of the insect brain and maybe find what you are looking for.
In general I would expect that the brain to body size ratio of most insects would be very similar. Also, the insect brain is closely associated with the other structures of the larger nervous system so it isn't so easy to define exactly where the insect brain begins and where it ends, so to speak. As the link above points out, many insects can go on living and functioning for quite some time even without a head, so it's clear that the insect brain isn't doing the same thing (or even similar things) to what the mammalian brain is doing.