Hmm... you're absolutely correct, Saturnyne. Calling your theory stupid doesn't disprove it - it merely indicates that I believe your theory isn't worth disproving.
But ok, let's take a look at it.
Are the Bugs using humans as genetic stock? Your theory is 'yes - they are mutating the humans into aliens'.
My answer is 'no - it is a stupid idea.'
But since you're not too satisfied with this answer, let's try a different one
.
No. While it is impossible to deny that the Bugs know a good deal about DNAs and possibly genetic engineering, there is no reason to suspect that they are capable of altering an existing human being into one of them.
Secondly, what would be the point? The process would probably waste as much resources as simple cloning would, and is therefore obsolete even before it is invented.
Unless, of course, the aliens never invented cloning, and they somehow developed this concept instead. Well, anything's possible, I suppose, but what would be the point of the development of such a process? The bugs already appear to have a hive structure (see references to the Mother Creature - and this name alone dismisses your theory that maybe they can't reproduce), and therefore we can guess that their reproduction rates are much faster than ours. So, there's no point.
Furthermore, even in societies where reproduction is relatively slow (like ours), cloning or cloning-like processes are not developed to speed up the society's reproduction, but merely that of subservient creatures, such as sheep and pigs. The aliens undoubtedly think differently, but does this mean that they consider it worthwhile to clone creatures which are not subservient - such as soldiers, who by definition are anything but subservient. Well, let's imagine what our dear Mother Creature might think about this. If soldiers can be cloned, than sooner or later some smart-ass bug will decide that they could speed up the production of workers by the same process. The Mother Creature thus faces the risk of becoming useless, and losing her dominant position in society. Or worse - some smart-ass bug might come up with the bright idea of cloning the Mother Creature. Thus, our dear Mother Creature finds herself in an even more disturbing position - direct competition.
In short, the Mother Creature is mightily displeased with the prospect of cloning or cloning-like processes, and uses her dominant position in society to force an end to the research.
A lot of what I said above is probably gibberish (but it sounded persuasive when I wrote it
), but I think I have a few valid points in there. Doth this answer please thee, or shall I need to come up with more gibberish?
Oh, there is one more thing. You ask why they would bother researching into humans. The guy (whatever his name was) who was the first to climb Mt. Everest was once asked
why he did it. His answer will suffice to answer your question, too:
"Because it's there."