I encountered the problem below while designing one of my mosquitoes (which never did get folded) and solved it as illustrated, creating a useful box pleating gadget in the process. Later, while looking at the CP for Dr. Lang's Aedes aegypti, I noticed a variation on the same solution being used by Lang that lead to some interesting discoveries.
Solution:
This method works well, but doesn’t look very nice. There is the large square shape near the top of the flap and quite a few other creases that are all visually distracting. Furthermore, if I folded a model and these creases were showing on one of the surfaces, perhaps the wing casings of a beetle, I would be dissatisfied with the result. Wouldn't it be nice then, if it were possible to just take the folded form of the gadget and stretch it down to the very base of the flap (shown by dotted line in diagrams) so it was out of the way and easily hidden away inside the model? As it turns out this is not only possible, but relatively simple, just as nice as it sounds, and seemingly applicable to any length of flap.