I think Ambion might have a better product called RNAlater-Ice. It is specifically designed for taking a sample previously stored at -80C or LN2 and switching to room temp stabilization.
I don't think the RNAlater or Protect would penetrate a frozen tissue- or it has not been tested for that.
You could also just pulverize your larvae in a high guanidine/ BME containing lysis buffer and store the lysate at -80C. Then, when you are ready for extraction, you can just thaw and go direct to processing.
We used to store cell lysates like this, passing the lysate through a needle and syringe to make sure everything was liquified and the DNA was completely sheared before storing.
(not affliated with Ambion)