Well, I'm sure Lavos as he landed had the I.Q. of a common insectual parasite. After so much DNA, you'd figure he'd be SOMEHOW smarter. Later on... Well.. It's been said that linking with the Flame links with Lavos... And Q.Zeal became a power-hungry murderous whore, so I'd say that he can communicate, with the Flame being the one that conveys the message in a way humans can understand.
The supposition that Lavos was nothing more than a parasite is impossible. Firstly, his biotechnology evident in the core show him to be scientifically far more advanced than humanity. Unless he was created by another race - in which case I would call Occam's Razor forward - he himself has quite a bit of skill. Even his title, the Infamous Immortal, connotes a more cunning mind. Yes, he may be a parasite... but in the Chrono world, humanity is shown as a parasite as well. He is a manisfestation of all that is evil, all the wickedness that humanity could become, and what the other races are sure they will become. Of course, humanity seems to vindicate itself more than once, but that warning stands. For that reason I would disagree with the supposition this thread puts forward: it is very evident that Lavos instilled the evil in humanity. Sort of a reverse of the old philisophical motif which spoke of humanity being part base earthly, bestial matter, and part divine spark. Well, here it is the divine spark that seems to be evil, and the bestial that is the good.
Lavos remains a dark lord, and no mere bug. He might act like a bug, have the instincts of a parasite, but that is no different than humanity having the traits of monkeys. We ARE different than monkeys, just as he is different than a parasite. Furthermore, dictates of right and wrong do govern him - good and evil are not in the eye of the beholder, as there are absolutes that any would agree to. Lavos knows this, he has a sense of right and wrong, and that what he does might be wrong. He seems almost a bitter creature. Think about Terra Tower, and his words there. He wonders at the destruction he causes, and why it is neccessary to destroy worlds in order to preserve himself - a motif echoed on a smaller scale in many actions of humanity in the game (ie. Water Dragon Isle, Hydra Swamp, etc.) Lavos is asking himself those same questions which humanity ought to: is it really survival of the fittest when one has sentience? Does one's own survival trump all else? Of course, he does wicked things, and has the capability of great evil, and by whatever cause his being is one of immense destructive power... but he seems to be at odds and frustrated with that, frustrated to the point of extreme anger. Again, this is not meant to be coming from humans, but rather an explanations of why humans themselves are so divided: capable of great things, good and evil alike. The main supposition is that, without Lavos, humanity is nothing more than an animal, and a natural part of the world. With Lavos, humanity becomes a sort of tainted renegade cell within a host - but one that keeps fighting off invaders very effectively, it seems, though being a bit of a danger to the host itself. Think about it this way: if you got a disease which began mutating your cells, and these cells were in danger of killing you, but the cells themselves fought off the disease repeatedly, saving your life, wouldn't the thought toward that be ambivalent? But in the end, remember this: it is the Frozen Flame that advanced and supposedly tainted humanity. The Frozen Flame was the essence of Lavos, a split part from him. I find it highly unlikely that humanity was the cause of his actions.
Anyway, just because Lavos acts parasitically does not mean that he is not sentient. Most evidence seems to point to him being both sentient and parasitical.
