A devastating earthquake releases a horde of mutant cockroaches with the pesky ability to start fires. And that's not good news for a small, isolated California desert town that stands in the way of these creepy-crawlies. The whole mess begins to obsess a science professor (Bradford Dillman) to the point of madness. This ecological disaster flick, directed by Jeannot Szwarc, was legendary horror producer William Castle's final film.
probably not the "bug" you're recommending though
I was thinking this Bug