I've just noticed that biodrones don't explode when killed by melee weapons. Is this bug or feature? I vaguely remember they exploded in the DOS version.
I'm attaching a save where you can test it. I have a MC'd biodrone that you can move in front of aquatoid with thermic lance (the aquatiod will reaction-fire, usually killing the bidorone). Or you can MC a triscene in the back and chew the biodrone up. If you use other aliens to shoot the biodrone, it will explode as usual.