Adlinsey,
First off, kudos to your diligence with working through this problem. You clearly have a grasp of some of the core concepts of conditional reasoning.
However, I encourage you not to create a complicated morass for yourself when you're dealing with LR questions. Occasionally, I observe students diving in headfirst into symbolizations of stimuli without giving adequate thought to what is significant and what is insignificant. In effect, sometimes people do not give the necessary thought to the organization of the problem before they get started with the symbols. Symbolization is not a substitute for your own reasoning; it is a supplement and an aid to it.
Thus when you first read through a stimulus, read it all the way through. Try to describe to yourself what's going on. In this case, you might observe something like this:
"Okay, so these insects can use instincts to do complex stuff, instinct doesn't use reasoning or need a lot of neurons. Also, it says non-instinct needs a lot of neurons, and no insects have a lot of neurons."
Try to distill the stimulus down to its key components. What matters? Well, if you spot conditional language, you need to zero in on it. Establish common terms or ideas. Without symbolizing, try to prephrase any connections you observe. Perhaps ask youself: "So what? Do I know anything else from this?"
You might notice that it seems pretty clear that insects can't do non-instinct stuff, so they must be stuck with only instinct.
That's your prephrase. If you got this, you're good to go. If you want to double check your reasoning with symbols, be sure to keep your variables consistent and concise. Do not add extra, unnecessary steps.
For instance, this stimulus can concisely be represented as:
1) IB
~R
2) ~IB
MNC
3) Insects
~MNC
From the contrapositive of (2) we get ~MNC
IB. From (3) combined with the contrapositive of (2) we get:
Insects
~MNC
IB
Notice that this is a fun academic exercise but likely more than what is necessary to get the question right.